US20110166370A1

US20110166370A1 - Scattered Branched-Chain Fatty Acids And Biological Production Thereof

Info

Publication number: US20110166370A1
Application number: US13/004,077
Authority: US
Inventors: Charles Winston Saunders; Jun Xu; II Leo Timothy Laughlin; Zubin Sarosh Khambatta; Phillip Richard Green
Original assignee: Individual
Current assignee: Procter and Gamble Co
Priority date: 2010-01-12
Filing date: 2011-01-11
Publication date: 2011-07-07
Also published as: RU2012126807A; US20110171155A1; MX2012008140A; AU2011205370B2; JP2013517276A; EP2524049B1; BR112012017241A2; CA2783170A1; AU2011205370A1; CN103221030A; US8933131B2; JP5587429B2; BR112012017267A2; CN102791870A; PH12012501411A1; CN103221030B; WO2011088089A1; EP2524049A1; EP2523652A1; WO2011088088A1

Abstract

Methods and cells for producing scattered branched-chain fatty acids are provided. For example, the invention provides a method for producing branched-chain fatty acid comprising a methyl on one or more even number carbons. The method comprises culturing a cell comprising an exogenous or overexpressed polynucleotide comprising a nucleic acid sequence encoding a polypeptide that catalyzes the conversion of propionyl-CoA to methylmalonyl-CoA and/or an exogenous or overexpressed polynucleotide comprising a nucleic acid sequence encoding a polypeptide that catalyzes the conversion of succinyl-CoA to methylmalonyl-CoA, under conditions allowing expression of the polynucleotide(s) and production of branched-chain fatty acid. The cell produces more branched-chain fatty acid comprising a methyl on one or more even number carbons than an otherwise similar cell that does not comprise the polynucleotide(s). A cell that produces branched-chain fatty acid and the branched-chain fatty acid also are provided.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS AND INCORPORATION BY REFERENCE

This application claims priority to U.S. Provisional Patent Application No. 61/294,274, filed Jan. 12, 2010, which is hereby incorporated by reference in its entirety.

FIELD OF THE INVENTION

The invention relates to cells and methods for producing fatty acids, and more particularly relates to cells and methods for producing scattered branched-chain fatty acids.

BACKGROUND OF THE INVENTION

Branched-chain fatty acids are carboxylic acids with a methyl or ethyl branch on one or more carbons that can be either chemically synthesized or isolated from certain animals and bacteria. While certain bacteria, such as Escherichia coli, do not naturally produce branched-chain fatty acids, some bacteria, such as members of the genera Bacillus and Streptomyces, can naturally produce these fatty acids. For example, Streptomyces avermitilis and Bacillus subtilis both produce branched-chain fatty acids with from 14 to 17 total carbons, with the branches in the iso and anteiso positions (Cropp et al., Can. J. Microbiology 46: 506-14 (2000); De Mendoza et al., Biosynthesis and Function of Membrane Lipids, in Bacillus subtilis and Other Gram-Positive Bacteria, Sonenshein and Losick, eds., American Society for Microbiology (1993)). However, these organisms do not produce branched-chain fatty acids in amounts that are commercially useful. Another limitation of these natural organisms is that they apparently do not produce medium-chain branched-chain fatty acids, such as those with 11 or 13 carbons. In addition, if fatty acids having particular chain lengths, branches on particular carbons, or branches at positions other than the iso and anteiso positions are desired, these fatty acids may not be available or easily isolated from a natural organism in meaningful quantities.
As such, there remains a need for commercially useful, bacterially-produced, branched-chain fatty acids. In addition, there remains a need for a method of producing such branched-chain fatty acids.

SUMMARY OF THE INVENTION

Methods and cells for producing scattered branched-chain fatty acids are provided. In certain embodiments, the method for producing branched-chain fatty acids in a cell includes expressing in the cell one or more recombinant polypeptides that catalyze the conversion of methylmalonyl-CoA to methylmalonyl-ACP; and culturing the cell under conditions suitable for producing the polypeptide, such that branched-chain fatty acids are produced.
Also provided is a method for producing branched-chain fatty acids in a cell, the method including expressing in the cell one or more recombinant polypeptides that increase the production of methylmalonyl-CoA in the cell; and culturing the cell under conditions suitable for producing the recombinant polypeptide, such that branched-chain fatty acids are produced.
In certain embodiments, a method for producing branched-chain fatty acids in a cell is provided, the method including expressing in the cell a polypeptide that has propionyl-CoA synthetase activity; inhibiting propionylation of the propionyl-CoA synthetase; and culturing the cell under conditions suitable for producing the polypeptide, such that branched-chain fatty acids are produced.
Further provided is a method for producing branched-chain fatty acids in a cell, the method including expressing in the cell a polypeptide that has methylmalonyl-CoA mutase activity; expressing in a cell a polypeptide that has methylmalonyl-CoA epimerase activity; and culturing the cell under conditions suitable for producing the polypeptides, such that branched-chain fatty acids are produced.
A composition comprising a mixture of biologically-produced branched-chain fatty acids is also provided. The composition can include branched-chain fatty acids having a chain length of C12 to C16 and from about 1 to about 3 methyl branches positioned on one or more even-numbered carbons.
In certain embodiments, a method for producing branched-chain fatty acids in a cell is provided, the method including expressing in the cell one or more recombinant polypeptides that increase the production of methylmalonyl-CoA in the cell; expressing in the cell a recombinant polypeptide that catalyzes the conversion of methylmalonyl-CoA to methylmalonyl-ACP; and culturing the cell under conditions suitable for producing the recombinant polypeptide, such that branched-chain fatty acids are produced.
In addition, in certain embodiments, a method for producing branched-chain fatty acids in a cell is provided, the method including expressing in the cell one or more recombinant polypeptides that increase the production of methylmalonyl-CoA in the cell; expressing in the cell a recombinant polypeptide that catalyzes the conversion of methylmalonyl-CoA to methylmalonyl-ACP; expressing in the cell a recombinant thioesterase; and culturing the cell under conditions suitable for producing the recombinant polypeptide, such that branched-chain fatty acids are produced.
Also provided is a method for producing branched-chain fatty acids in a cell, the branched-chain fatty acids having a chain length from about 10 to 18 carbons and branching at the second carbon. The method includes modifying the cell to increase carbon flow to methylmalonyl-CoA; and culturing the cell under conditions suitable for carbon flow to methylmalonyl-CoA to be increased, such that branched-chain fatty acids having a chain length from about 10 to about 18 carbons and branching at the second carbon are produced. In certain embodiments, the branching can be on the fourth, sixth, eighth, tenth, or twelfth carbon.
In certain embodiments, a method for producing branched-chain fatty acids in a cell is provided, the branched-chain fatty acids having a chain length from about 10 to 18 carbons and branching at the second carbon. The method includes modifying the cell to generate methylmalonyl-ACP from methylmalonyl-CoA; and culturing the cell under conditions suitable for generation of methylmalonyl-ACP from methylmalonyl-CoA, such that branched-chain fatty acids having a chain length from about 10 to about 18 carbons and branching at the second carbon are produced. In certain embodiments, the branching can be on the fourth, sixth, eighth, tenth, or twelfth carbon.
A method for producing modified fatty acids in a cell is also provided, the method including providing a cell having type II fatty acid synthase activity; expressing in the cell one or more recombinant polypeptides that catalyze formation of at least one intermediate metabolite, wherein the at least one intermediate metabolite is incorporated by the type II fatty acid synthase; and culturing the cell under conditions suitable for producing the recombinant polypeptide, such that modified fatty acids are produced.
Further provided is an Escherichia cell that produces branched-chain fatty acids having a chain length from about 10 to about 18 carbons and comprising one or more methyl branches on one or more even-numbered carbons.
The invention further provides a method for producing branched-chain fatty acid comprising a methyl on one or more even number carbons. The method comprises culturing a cell comprising (aa) an exogenous or overexpressed polynucleotide comprising a nucleic acid sequence encoding a polypeptide that catalyzes the conversion of propionyl-CoA to methylmalonyl-CoA and/or (bb) an exogenous or overexpressed polynucleotide comprising a nucleic acid sequence encoding a polypeptide that catalyzes the conversion of succinyl-CoA to methylmalonyl-CoA. The cell is cultured under conditions allowing expression of the polynucleotide(s) and production of branched-chain fatty acid. Optionally, the method further comprises extracting from the culture the branched-chain fatty acid or a product of the branched-chain fatty acid. Also provided is a cell comprising (i) an exogenous or overexpressed polynucleotide comprising a nucleic acid sequence encoding an acyl transferase lacking polyketide synthesis activity, and (ii) an exogenous or overexpressed polynucleotide comprising a nucleic acid sequence encoding a propionyl-CoA carboxylase and/or an exogenous or overexpressed polynucleotide comprising a nucleic acid sequence encoding a methylmalonyl-CoA mutase, which are expressed in the cell. The cell produces more branched-chain fatty acid comprising a methyl on one or more even number carbons than an otherwise similar cell that does not comprise the polynucleotide(s).
The following numbered paragraphs each succinctly define one or more exemplary variations of the invention:
1. A method for producing branched-chain fatty acid comprising a methyl on one or more even number carbons, the method comprising culturing a cell comprising
(aa) an exogenous or overexpressed polynucleotide comprising a nucleic acid sequence encoding a polypeptide that catalyzes the conversion of propionyl-CoA to methylmalonyl-CoA and/or (bb) an exogenous or overexpressed polynucleotide comprising a nucleic acid sequence encoding a polypeptide that catalyzes the conversion of succinyl-CoA to methylmalonyl-CoA, under conditions allowing expression of the polynucleotide(s) and production of branched-chain fatty acid, wherein the cell produces more fatty acid comprising a methyl on one or more even number carbons than an otherwise similar cell that does not comprise the polynucleotide(s).
2. The method of paragraph 1 further comprising extracting from culture the branched-chain fatty acid or a product of the branched-chain fatty acid.
3. The method of paragraph 1 or paragraph 2, wherein the polypeptide that catalyzes the conversion of propionyl-CoA to methylmalonyl-CoA is a propionyl-CoA carboxylase and/or the polypeptide that catalyzes the conversion of succinyl-CoA to methylmalonyl-CoA is a methylmalonyl-CoA mutase.
4. The method of paragraph 3, wherein (i) the propionyl-CoA carboxylase is Streptomyces coelicolor PccB and AccA1 or PccB and AccA2 and/or (ii) the methylmalonyl-CoA mutase is Janibacter sp. HTCC2649 methylmalonyl-CoA mutase, S. cinnamonensis MutA and MutB, or E. coli Sbm.
5. The method of paragraph 3, wherein (i) the methylmalonyl-CoA mutase comprises an amino acid sequence having at least about 80% sequence identity to the amino acid sequence set forth in SEQ ID NOs: 3, 4, or 28 and/or (ii) the propionyl-CoA carboxylase comprises an amino acid sequence having at least about 80% sequence identity to the amino acid sequence set forth in SEQ ID NOs: 9 and 10.
6. The method of any one of paragraphs 3-5, wherein the cell comprises an exogenous or overexpressed polynucleotide comprising a nucleic acid sequence encoding a methylmalonyl-CoA mutase and further comprises an exogenous or overexpressed polynucleotide comprising a nucleic acid sequence encoding a methylmalonyl-CoA epimerase.
7. The method of any one of paragraphs 1-6, wherein the cell further comprises an exogenous or overexpressed polynucleotide encoding an acyl transferase lacking polyketide synthesis activity and/or an exogenous or overexpressed polynucleotide comprising a nucleic acid sequence encoding a thioesterase.
8. The method of paragraph 7, wherein the acyl transferase is FabD, an acyl transferase domain of a polyketide synthase, or an acyl transferase domain of Mycobacterium mycocerosic acid synthase.
9. The method of any one of paragraphs 1-8, wherein the cell has been modified to attenuate endogenous methylmalonyl-CoA mutase activity, endogenous methylmalonyl-CoA decarboxylase activity, and/or endogenous acyl transferase activity.
10. The method of any one of paragraphs 1-9, wherein the cell produces a Type II fatty acid synthase.
11. The method of any one of paragraphs 1-10, wherein the cell is Escherichia coli.
12. A branched-chain fatty acid produced by the method of any one of paragraphs 1-11.
13. A cell comprising: (i) an exogenous or overexpressed polynucleotide comprising a nucleic acid sequence encoding an acyl transferase lacking polyketide synthesis activity, and (ii) an exogenous or overexpressed polynucleotide comprising a nucleic acid sequence encoding a propionyl-CoA carboxylase and/or an exogenous or overexpressed polynucleotide comprising a nucleic acid sequence encoding a methylmalonyl-CoA mutase, wherein the polynucleotide(s) are expressed and the cell produces more branched-chain fatty acid comprising a methyl on one or more even number carbons than an otherwise similar cell that does not comprise the polynucleotide(s).
14. The cell of paragraph 13, wherein (i) the propionyl-CoA carboxylase is Streptomyces coelicolor PccB and AccA1 or PccB and AccA2 and/or (ii) the methylmalonyl-CoA mutase is Janibacter sp. HTCC2649 methylmalonyl-CoA mutase, S. cinnamonensis MutA and MutB, or E. coli Sbm.
15. The cell of paragraph 13, wherein (i) the methylmalonyl-CoA mutase comprises an amino acid sequence having at least about 80% sequence identity to the amino acid sequence set forth in SEQ ID NOs: 3, 4, or 28 and/or (ii) the propionyl-CoA carboxylase comprises an amino acid sequence having at least about 80% sequence identity to the amino acid sequence set forth in SEQ ID NOs: 9 and 10.
16. The cell of any one of paragraphs 13-15, wherein the cell comprises an exogenous or overexpressed polynucleotide comprising a nucleic acid sequence encoding a methylmalonyl-CoA mutase and further comprises an exogenous or overexpressed polynucleotide comprising a nucleic acid sequence encoding a methylmalonyl-CoA epimerase.
17. The cell of any one of paragraphs 13-16, wherein the acyl transferase is FabD, an acyl transferase domain of a polyketide synthase, or an acyl transferase domain of Mycobacterium mycocerosic acid synthase.
18. The cell of any one of paragraphs 13-17, wherein the cell further comprises an exogenous or overexpressed polynucleotide comprises a nucleic acid sequence encoding a thioesterase.
19. The cell of any one of paragraphs 13-18, wherein the cell has been modified to attenuate endogenous methylmalonyl-CoA mutase activity, endogenous methylmalonyl-CoA decarboxylase activity, and/or endogenous acyl transferase activity.
20. The cell of any one of paragraphs 13-19, wherein the cell is Escherichia coli.
21. A method for producing branched-chain fatty acids in a cell comprising: a. expressing in the cell one or more recombinant polypeptides that catalyze the conversion of methylmalonyl-CoA to methylmalonyl-ACP; and b. culturing the cell under conditions suitable for producing the polypeptide, such that branched-chain fatty acids are produced.
22. The method of paragraph 21, wherein the polypeptide is an acyl transferase.
23. The method of paragraph 21, wherein the polypeptide is encoded by fabD.
24. The method of paragraph 22, wherein the polypeptide is a polyketide synthase or a portion thereof.
25. The method of paragraph 21, wherein the polypeptide is a Mycobacterium mycocerosic acid synthase or a portion thereof
26. The method of paragraph 21, wherein the polypeptide has at least about 60% sequence identity to a sequence set forth in SEQ ID NO: 19.
27. The method of paragraph 21, wherein the method further includes expressing in the cell a polypeptide that encodes an exogenous thioesterase.
28. The method of paragraph 21, wherein the cell is an Escherichia cell.
29. The method of paragraph 21, wherein the cell produces higher levels of branched-chain fatty acids after expression of the polypeptide than it did prior to expression of the polypeptide.
30. The method of paragraph 21, wherein the branched-chain fatty acids comprise one or more methyl branches.
31. The method of paragraph 30, wherein the one or more methyl branches are on even numbered carbons.
32. The method of paragraph 21, wherein the branched-chain fatty acids are not naturally produced in the cell.
33. Branched-chain fatty acids produced by the method of paragraph 21.
34. A cell comprising at least one recombinant polypeptide that catalyzes the conversion of methylmalonyl-CoA to methylmalonyl-ACP, wherein the cell comprising the recombinant polypeptide produces more branched-chain fatty acids than an otherwise similar cell that does not comprise the recombinant polypeptide.
35. A method for producing branched-chain fatty acids in a cell comprising: a. expressing in the cell one or more recombinant polypeptides that increase the production of methylmalonyl-CoA in the cell; and b. culturing the cell under conditions suitable for producing the recombinant polypeptide, such that branched-chain fatty acids are produced.
36. The method of paragraph 35, wherein expression of the polypeptide results in increased propionyl-CoA synthetase activity in the cell.
37. The method of paragraph 35, wherein the polypeptide has propionyl-CoA carboxylase activity.
38. The method of paragraph 35, wherein the polypeptide has at least about 60% sequence identity to a sequence set forth in SEQ ID NO: 9 or SEQ ID NO: 10.
39. The method of paragraph 35, wherein the method further includes expressing in the cell a polypeptide that encodes an exogenous thioesterase.
40. The method of paragraph 35, wherein the cell is an Escherichia cell.
41. The method of paragraph 35, wherein the cell produces higher levels of branched-chain fatty acids after expression of the polypeptide than it did prior to expression of the polypeptide.
42. The method of paragraph 35, wherein the branched-chain fatty acids comprise one or more methyl branches.
43. The method of paragraph 42, wherein the one or more methyl branches are on even numbered carbons.
44. The method of paragraph 35, wherein the branched-chain fatty acids are not naturally produced in the cell.
45. Branched-chain fatty acids produced by the method of paragraph 35.
46. A cell comprising at least one recombinant polypeptide that increases the production of methylmalonyl-CoA in the cell, wherein the cell comprising the recombinant polypeptide produces more branched-chain fatty acids than an otherwise similar cell that does not comprise the recombinant polypeptide.
47. A method for producing branched-chain fatty acids in a cell comprising: a. expressing in the cell a polypeptide that has propionyl-CoA synthetase activity; b. inhibiting propionylation of the propionyl-CoA synthetase; and c. culturing the cell under conditions suitable for producing the polypeptide, such that branched-chain fatty acids are produced.
48. The method of paragraph 47, wherein the polypeptide does not include a lysine that is subject to propionylation.
49. The method of paragraph 47, wherein step c) includes providing a source of resveratrol into a culture medium used to culture the cell.
50. The method of paragraph 47, wherein the cell does not include an N-acetyltransferase enzyme responsible for propionylation of the propionyl-CoA synthetase.
51. The method of paragraph 47, wherein the polypeptide has at least about 60% sequence identity to the protein encoded by SEQ ID NO: 22.
52. The method of paragraph 47, wherein the cell contains increased enzymatic activity for removal of propionyl groups from one or more lysine residues of propionyl-CoA synthetase.
53. The method of paragraph 47, wherein the method further includes expressing in the cell a polypeptide that encodes an exogenous thioesterase.
54. The method of paragraph 47, wherein the cell is an Escherichia cell.
55. The method of paragraph 47, wherein the cell produces higher levels of branched-chain fatty acids after expression of the polypeptide than it did prior to expression of the polypeptide.
56. The method of paragraph 47, wherein the branched-chain fatty acids comprise one or more methyl branches.
57. The method of paragraph 56, wherein the one or more methyl branches are on even numbered carbons.
58. The method of paragraph 47, wherein the branched-chain fatty acids are not naturally produced in the cell.
59. Branched-chain fatty acids produced by the method of paragraph 47.
60. A method for producing branched-chain fatty acids in a cell comprising: a. expressing in the cell a polypeptide that has methylmalonyl-CoA mutase activity; b. expressing in a cell a polypeptide that has methylmalonyl-CoA epimerase activity; and c. culturing the cell under conditions suitable for producing the polypeptides, such that branched-chain fatty acids are produced.
61. The method of paragraph 60, wherein the methylmalonyl-CoA mutase polypeptide has at least about 60% sequence identity to a sequence set forth in SEQ ID NO: 3 or SEQ ID NO: 4.
62. The method of paragraph 60, wherein the methylmalonyl-CoA epimerase polypeptide has at least about 60% sequence identity to a sequence set forth in SEQ ID NO: 6.
63. The method of paragraph 60, wherein the method further includes expressing in the cell a polypeptide that encodes an exogenous thioesterase.
64. The method of paragraph 60, wherein the cell is an Escherichia cell.
65. The method of paragraph 60, wherein the cell produces higher levels of branched-chain fatty acids after expression of the polypeptide than it did prior to expression of the polypeptide.
66. The method of paragraph 60, wherein the branched-chain fatty acids comprise one or more methyl branches.
67. The method of paragraph 66, wherein the one or more methyl branches are on even numbered carbons.
68. The method of paragraph 60, wherein the branched-chain fatty acids are not naturally produced in the cell.
69. Branched-chain fatty acids produced by the method of paragraph 60.
70. A cell comprising recombinant polypeptides having methylmalonyl-CoA mutase activity and methylmalonyl-CoA epimerase activity, wherein the cell comprising the recombinant polypeptides produces more branched-chain fatty acids than an otherwise similar cell that does not comprise the recombinant polypeptide.
71. A composition comprising a mixture of biologically-produced branched-chain fatty acids, the branched-chain fatty acids having a chain length of C12 to C16 and from about 1 to about 3 methyl branches positioned on one or more even-numbered carbons.
72. A method for producing branched-chain fatty acids in a cell comprising: a. expressing in the cell one or more recombinant polypeptides that increase the production of methylmalonyl-CoA in the cell; b. expressing in the cell a recombinant polypeptide that catalyzes the conversion of methylmalonyl-CoA to methylmalonyl-ACP; and c. culturing the cell under conditions suitable for producing the recombinant polypeptide, such that branched-chain fatty acids are produced.
73. The method of paragraph 72, wherein the cell has a deletion in a gene for a methylmalonyl-CoA decarboxylase.
74. The method of paragraph 72, wherein the cell additionally produces a recombinant polypeptide with a 3-ketoacyl-ACP synthase activity that recognizes methylmalonyl-ACP as a substrate.
75. A method for producing branched-chain fatty acids in a cell comprising: a. expressing in the cell one or more recombinant polypeptides that increase the production of methylmalonyl-CoA in the cell; b. expressing in the cell a recombinant polypeptide that catalyzes the conversion of methylmalonyl-CoA to methylmalonyl-ACP; c. expressing in the cell a recombinant thioesterase; and d. culturing the cell under conditions suitable for producing the recombinant polypeptide, such that branched-chain fatty acids are produced.
76. The method of paragraph 75, wherein the cell has a deletion in a gene for a methylmalonyl-CoA decarboxylase.
77. The method of paragraph 75, wherein the cell additionally produces a recombinant polypeptide with a 3-ketoacyl-ACP synthase activity that recognizes methylmalonyl-ACP as a substrate.
78. A method for producing branched-chain fatty acids in a cell, the branched-chain fatty acids having a chain length from about 10 to 18 carbons and branching at the second carbon, the method comprising: a. modifying the cell to increase carbon flow to methylmalonyl-CoA; and b. culturing the cell under conditions suitable for carbon flow to methylmalonyl-CoA to be increased, such that branched-chain fatty acids having a chain length from about 10 to about 18 carbons and branching at the second carbon are produced.
79. The method of paragraph 78, wherein the branching at the second carbon is a methyl branch.
80. A method for producing branched-chain fatty acids in a cell, the branched-chain fatty acids having a chain length from about 10 to 18 carbons and branching at the fourth carbon, the method comprising: a. modifying the cell to increase carbon flow to methylmalonyl-CoA; and b. culturing the cell under conditions suitable for carbon flow to methylmalonyl-CoA to be increased, such that branched-chain fatty acids having a chain length from about 10 to about 18 carbons and branching at the fourth carbon are produced.
81. The method of paragraph 80, wherein the branching at the fourth carbon is a methyl branch.
82. A method for producing branched-chain fatty acids in a cell, the branched-chain fatty acids having a chain length from about 10 to 18 carbons and branching at the sixth carbon, the method comprising: a. modifying the cell to increase carbon flow to methylmalonyl-CoA; and b. culturing the cell under conditions suitable for carbon flow to methylmalonyl-CoA to be increased, such that branched-chain fatty acids having a chain length from about 10 to about 18 carbons and branching at the sixth carbon are produced.
83. The method of paragraph 82, wherein the branching at the sixth carbon is a methyl branch.
84. A method for producing branched-chain fatty acids in a cell, the branched-chain fatty acids having a chain length from about 12 to 18 carbons and branching at the eighth carbon, the method comprising: a. modifying the cell to increase carbon flow to methylmalonyl-CoA; and b. culturing the cell under conditions suitable for carbon flow to methylmalonyl-CoA to be increased, such that branched-chain fatty acids having a chain length from about 12 to about 18 carbons and branching at the eighth carbon are produced.
85. The method of paragraph 84, wherein the branching at the eighth carbon is a methyl branch.
86. A method for producing branched-chain fatty acids in a cell, the branched-chain fatty acids having a chain length from about 14 to 18 carbons and branching at the tenth carbon, the method comprising: a. modifying the cell to increase carbon flow to methylmalonyl-CoA; and b. culturing the cell under conditions suitable for carbon flow to methylmalonyl-CoA to be increased, such that branched-chain fatty acids having a chain length from about 14 to about 18 carbons and branching at the tenth carbon are produced.
87. The method of paragraph 86, wherein the branching at the tenth carbon is a methyl branch.
88. A method for producing branched-chain fatty acids in a cell, the branched-chain fatty acids having a chain length from about 16 to 18 carbons and branching at the twelfth carbon, the method comprising: a. modifying the cell to increase carbon flow to methylmalonyl-CoA; and b. culturing the cell under conditions suitable for carbon flow to methylmalonyl-CoA to be increased, such that branched-chain fatty acids having a chain length from about 16 to about 18 carbons and branching at the twelfth carbon are produced.
89. The method of paragraph 88, wherein the branching at the twelfth carbon is a methyl branch.
90. A method for producing branched-chain fatty acids in a cell, the branched-chain fatty acids having a chain length from about 10 to 18 carbons and branching at the second carbon, the method comprising: a. modifying the cell to generate methylmalonyl-ACP from methylmalonyl-CoA; and b. culturing the cell under conditions suitable for generation of methylmalonyl-ACP from methylmalonyl-CoA, such that branched-chain fatty acids having a chain length from about 10 to about 18 carbons and branching at the second carbon are produced.
91. The method of paragraph 90, wherein the branching at the second carbon is a methyl branch.
92. A method for producing branched-chain fatty acids in a cell, the branched-chain fatty acids having a chain length from about 10 to 18 carbons and branching at the fourth carbon, the method comprising: a. modifying the cell to generate methylmalonyl-ACP from methylmalonyl-CoA; and b. culturing the cell under conditions suitable for generation of methylmalonyl-ACP from methylmalonyl-CoA, such that branched-chain fatty acids having a chain length from about 10 to about 18 carbons and branching at the fourth carbon are produced.
93. The method of paragraph 92, wherein the branching at the fourth carbon is a methyl branch.
94. A method for producing branched-chain fatty acids in a cell, the branched-chain fatty acids having a chain length from about 10 to 18 carbons and branching at the sixth carbon, the method comprising: a. modifying the cell to generate methylmalonyl-ACP from methylmalonyl-CoA; and b. culturing the cell under conditions suitable for generation of methylmalonyl-ACP from methylmalonyl-CoA, such that branched-chain fatty acids having a chain length from about 10 to about 18 carbons and branching at the sixth carbon are produced.
95. The method of paragraph 94, wherein the branching at the sixth carbon is a methyl branch.
96. A method for producing branched-chain fatty acids in a cell, the branched-chain fatty acids having a chain length from about 12 to 18 carbons and branching at the eighth carbon, the method comprising: a. modifying the cell to generate methylmalonyl-ACP from methylmalonyl-CoA; and b. culturing the cell under conditions suitable for generation of methylmalonyl-ACP from methylmalonyl-CoA, such that branched-chain fatty acids having a chain length from about 12 to about 18 carbons and branching at the eighth carbon are produced.
97. The method of paragraph 96, wherein the branching at the eighth carbon is a methyl branch.
98. A method for producing branched-chain fatty acids in a cell, the branched-chain fatty acids having a chain length from about 14 to 18 carbons and branching at the tenth carbon, the method comprising: a. modifying the cell to generate methylmalonyl-ACP from methylmalonyl-CoA; and b. culturing the cell under conditions suitable for generation of methylmalonyl-ACP from methylmalonyl-CoA, such that branched-chain fatty acids having a chain length from about 14 to about 18 carbons and branching at the tenth carbon are produced.
99. The method of paragraph 98, wherein the branching at the tenth carbon is a methyl branch.
100. A method for producing branched-chain fatty acids in a cell, the branched-chain fatty acids having a chain length from about 16 to 18 carbons and branching at the twelfth carbon, the method comprising: a. modifying the cell to generate methylmalonyl-ACP from methylmalonyl-CoA; and b. culturing the cell under conditions suitable for generation of methylmalonyl-ACP from methylmalonyl-CoA, such that branched-chain fatty acids having a chain length from about 16 to about 18 carbons and branching at the twelfth carbon are produced.
101. The method of paragraph 100, wherein the branching at the twelfth carbon is a methyl branch.
102. A method for producing modified fatty acids in a cell comprising: a. providing a cell having type II fatty acid synthase activity; b. expressing in the cell one or more recombinant polypeptides that catalyze formation of at least one intermediate metabolite, wherein the at least one intermediate metabolite is incorporated by the type II fatty acid synthase; and c. culturing the cell under conditions suitable for producing the recombinant polypeptide, such that modified fatty acids are produced.
103. The method of paragraph 102, wherein the cell is an Escherichia cell.
104. The method of paragraph 102, wherein the intermediate metabolite is methylmalonyl-ACP.
105. The method of paragraph 102, wherein the polypeptide(s) catalyze the conversion of methylmalonyl-CoA to methylmalonyl-ACP.
106. The method of paragraph 102, wherein the cell produces higher levels of modified fatty acids after expression of the polypeptide than it did prior to expression of the polypeptide.
107. The method of paragraph 102, wherein the modified fatty acids comprise one or more methyl branches on even-numbered carbons.
108. The method of paragraph 102, wherein the polypeptide is an acyl transferase.
109. The method of paragraph 102, wherein the polypeptide is encoded by fabD.
110. The method of paragraph 102, wherein the polypeptide is a polyketide synthase or a portion thereof.
111. The method of paragraph 102, wherein the polypeptide is a Mycobacterium mycocerosic acid synthase or a portion thereof.
112. An Escherichia cell that produces branched-chain fatty acids having a chain length from about 10 to about 18 carbons and comprising one or more methyl branches on one or more even-numbered carbons.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a mutA nucleotide sequence (SEQ ID NO: 1).

FIG. 2 is a mutB nucleotide sequence (SEQ ID NO: 2).

FIG. 3 is a MutA protein sequence (SEQ ID NO: 3).

FIG. 4 is a MutB protein sequence (SEQ ID NO: 4).

FIG. 5 is a methylmalonyl-CoA epimerase nucleotide sequence (SEQ ID NO: 5).

FIG. 6 is a methylmalonyl-CoA epimerase protein sequence (SEQ ID NO: 6).

FIG. 7 is a DNA sequence for accA1 (GenBank Accession No. AF113603.1) (SEQ ID NO: 7).

FIG. 8 is a DNA sequence for pccB (GenBank Accession No. AF113605.1) (SEQ ID NO: 8).

FIG. 9 is a protein sequence for AccA1 (SEQ ID NO: 9).

FIG. 10 is a protein sequence for PccB (SEQ ID NO: 10).

FIG. 11 shows element 1 including the P_Llac0-1sequence and the phage T7 gene10 ribosome binding site (SEQ ID NO: 11).

FIG. 12 shows element 2 including the optimized accA1 gene sequence (SEQ ID NO: 12).

FIG. 13 shows element 3 including the spacer sequence (SEQ ID NO: 13).

FIG. 14 shows element 4 including the optimized pccB sequence (SEQ ID NO: 14).

FIG. 15 is a synthetic sequence for propionyl-CoA carboxylase gene expression (SEQ ID NO: 15).

FIG. 16 is the forward primer sequence for PrpE (SEQ ID NO: 16).

FIG. 17 is the reverse primer sequence for PrpE (SEQ ID NO: 17).

FIG. 18 is the MMAT domain sequence from Mycobacterium bovis BCG (SEQ ID NO: 18).

FIG. 19 is a protein sequence for the Mycobacterium bovis BCG MAS (GenBank Accession No. YP_—979046) (SEQ ID NO: 19).

FIG. 20 is a codon-optimized MMAT domain DNA sequence from Mycobacterium bovis BCG (SEQ ID NO: 20).

FIG. 21 is an alignment of a codon-optimized MMAT domain from Mycobacterium bovis BCG with the original sequence (SEQ ID NOs: 20 and 21).

FIG. 22 is the protein sequence of Salmonella enterica propionyl CoA synthase PrpE (GenBank Accession No. AAC44817) (SEQ ID NO: 22).

FIG. 23 is the DNA sequence of Salmonella enterica propionyl CoA synthase PrpE (SEQ ID NO. 23).

FIG. 24 is a bar graph illustrating methylmalonyl-CoA production (ng/ml) in E. coli strain K27-Z1 harboring pTrcHisA pZA31 (control), pZA31 mutAB Ss epi (MutAB Epi), pTrcHisA Ec sbm (Sbm), or pTrcHisA Ec sbm pZA31 Mb mmat (Sbm/Mmat). No methylmalonyl-CoA was identified in the control sample; the figure indicates the background level of detection.

FIG. 25 is a bar graph illustrating methylmalonyl-CoA production (ng/ml) in E. coli BW25113 (control) and BW25113 harboring pZA31-accA1-pccB (Pcc). No methylmalonyl-CoA was identified in the control sample; the figure indicates the background level of detection. Two biological replicates are represented.

FIG. 26 is a two-dimensional (2D) representation of the 2D Total Ion Chromatogram resulting from a sample of fatty acid produced by BL21 Star (DE3) E. coli harboring pTrcHisA Ec sbm So ce epi pZA31 mmat. Light areas on the figure indicate the presence of sample material. Peak names and arrows indicate samples that were further characterized by mass spectrometry.

FIG. 27 is a two-dimensional (2D) representation of the 2D Total Ion Chromatogram resulting from a sample produced by a control strain, BL21 Star (DE3) E. coli harboring pTrcHisA pZA31. No branched-chain fatty acid was detected. Arrows indicate the presence of straight-chain fatty acid derivatives of the indicated chain length.

FIG. 28 is a representation of the mass spectra of

peaks

54, 55, and 57 identified in FIG. 26. Eight- and ten-carbon branched-chain fatty acids are depicted in the top two profiles and were identified by the almost complete absence of the circled fragment. A twelve-branched fatty acid was tentatively identified and is depicted in the third profile.

DETAILED DESCRIPTION OF THE INVENTION

The invention relates to improved biological production of scattered branched-chain fatty acids. In addition, in certain embodiments, the invention provides improved compositions of biologically produced scattered branched-chain fatty acids having defined chain lengths with methyl branches at one or more even-numbered carbons within the fatty acid. In addition, in certain embodiments, the fatty acid length can be tailored to a predetermined length, such as, for example, to produce fatty acids with a backbone of C12 to C16. In certain embodiments, the methods and/or cells can produce a mixture of fatty acids having varied numbers of methyl branches, varied positions of the methyl branches, and varied length of the fatty acids, such as, for example, a mixture of fatty acids having a chain length of C12 to C16 and from about 0 to about 3 methyl branches positioned on one or more even-numbered carbons.
As used herein, “amplify,” “amplified,” or “amplification” refers to any process or protocol for copying a polynucleotide sequence into a larger number of polynucleotide molecules, e.g., by reverse transcription, polymerase chain reaction, and ligase chain reaction.
As used herein, an “antisense sequence” refers to a sequence that specifically hybridizes with a second polynucleotide sequence. For instance, an antisense sequence is a DNA sequence that is inverted relative to its normal orientation for transcription. Antisense sequences can express an RNA transcript that is complementary to a target mRNA molecule expressed within the host cell (e.g., it can hybridize to target mRNA molecule through Watson-Crick base pairing).
As used herein, “cDNA” refers to a DNA that is complementary or identical to an mRNA, in either single stranded or double stranded form.
As used herein, the carbons in fatty acids are numbered with the first carbon as part of the carboxylic acid group, and the second carbon (C2) adjacent to the first. The numbers continue so that the highest number carbon is farthest from the carboxylic acid group. “Even number” carbons include C2, C4, C6, C8, C10, C12, C14, and so on.
As used herein, “complementary” refers to a polynucleotide that can base pair with a second polynucleotide. Put another way, “complementary” describes the relationship between two single-stranded nucleic acid sequences that anneal by base-pairing. For example, a polynucleotide having the sequence 5′-GTCCGA-3′ is complementary to a polynucleotide with the sequence 5′-TCGGAC-3′.
As used herein, a “conservative substitution” refers to the substitution in a polypeptide of an amino acid with a functionally similar amino acid. Put another way, a conservative substitution involves replacement of an amino acid residue with an amino acid residue having a similar side chain. Families of amino acid residues having similar side chains have been defined within the art, and include amino acids with basic side chains (e.g., lysine, arginine, and histidine), acidic side chains (e.g., aspartic acid and glutamic acid), uncharged polar side chains (e.g., glycine, asparagine, glutamine, serine, threonine, tyrosine, and cysteine), nonpolar side chains (e.g., alanine, valine, leucine, isoleucine, proline, phenylalanine, methionine, and tryptophan), beta-branched side chains (e.g., threonine, valine, and isoleucine) and aromatic side chains (e.g., tyrosine, phenylalanine, tryptophan, and histidine).
As used herein, “encoding” refers to the inherent property of nucleotides to serve as templates for synthesis of other polymers and macromolecules. Unless otherwise specified, a “nucleotide sequence encoding an amino acid sequence” includes all nucleotide sequences that are degenerate versions of each other and that encode the same amino acid sequence.
As used herein, “endogenous” refers to polynucleotides, polypeptides, or other compounds that are expressed naturally or originate within an organism or cell. That is, endogenous polynucleotides, polypeptides, or other compounds are not exogenous. For instance, an “endogenous” polynucleotide or peptide is present in the cell when the cell was originally isolated from nature.
As used herein, “expression vector” refers to a vector comprising a recombinant polynucleotide comprising expression control sequences operatively linked to a nucleotide sequence to be expressed. For example, suitable expression vectors include, without limitation, autonomously replicating vectors or vectors integrated into the chromosome. In some instances, an expression vector is a viral-based vector.
As used herein, “exogenous” refers to any polynucleotide or polypeptide that is not naturally expressed or produced in the particular cell or organism where expression is desired. Exogenous polynucleotides, polypeptides, or other compounds are not endogenous.
As used herein, “hybridization” includes any process by which a strand of a nucleic acid joins with a complementary nucleic acid strand through base-pairing. Thus, the term refers to the ability of the complement of the target sequence to bind to a test (i.e., target) sequence, or vice-versa.
As used herein, “hybridization conditions” are typically classified by degree of “stringency” of the conditions under which hybridization is measured. The degree of stringency can be based, for example, on the melting temperature (T_m) of the nucleic acid binding complex or probe. For example, “maximum stringency” typically occurs at about T_m-5° C. (5° below the T_mof the probe); “high stringency” at about 5-10° C. below the T_m; “intermediate stringency” at about 10-20° below the T_mof the probe; and “low stringency” at about 20-25° C. below the T. Alternatively, or in addition, hybridization conditions can be based upon the salt or ionic strength conditions of hybridization and/or one or more stringency washes. For example, 6×SSC=very low stringency; 3×SSC=low to medium stringency; 1×SSC=medium stringency; and 0.5×SSC=high stringency. Functionally, maximum stringency conditions may be used to identify nucleic acid sequences having strict (i.e., about 100%) identity or near-strict identity with the hybridization probe; while high stringency conditions are used to identify nucleic acid sequences having about 80% or more sequence identity with the probe.
As used herein, “identical” or percent “identity” in the context of two or more polynucleotide or polypeptide sequences refers to two or more sequences that are the same or have a specified percentage of nucleotides or amino acid residues that are the same, when compared and aligned for maximum correspondence, as measured using sequence comparison algorithms or by visual inspection.
As used herein, “long-chain fatty acids” refers to fatty acids with aliphatic tails longer than 14 carbons. In some embodiments of the invention, long-chain fatty acids are provided that comprise 15, 16, 17, 18, 19, 20, 21, or 22 carbons in the carbon backbone.
As used herein, “medium-chain fatty acids” refers to fatty acids with aliphatic tails between 6 and 14 carbons. In certain embodiments, the medium-chain fatty acids can have from 11 to 13 carbons.
As used herein, “naturally-occurring” refers to an object that can be found in nature. For example, a polypeptide or polynucleotide sequence that is present in an organism (including viruses) that can be isolated from a source in nature and which has not been intentionally modified by man in the laboratory is naturally-occurring.
As used herein, “operably linked,” when describing the relationship between two DNA regions or two polypeptide regions, means that the regions are functionally related to each other. For example, a promoter is operably linked to a coding sequence if it controls the transcription of the sequence; a ribosome binding site is operably linked to a coding sequence if it is positioned so as to permit translation; and a signal sequence is operably linked to a peptide if it functions as a signal sequence, such as by participating in the secretion of the mature form of the protein.
As used herein, “overexpression” refers to expression of a polynucleotide to produce a product (e.g., a polypeptide or RNA) at a higher level than the polynucleotide is normally expressed in the host cell. An overexpressed polynucleotide is generally a polynucleotide native to the host cell, the product of which is generated in a greater amount than that normally found in the host cell. Overexpression is achieved by, for instance and without limitation, operably linking the polynucleotide to a different promoter than the polynucleotide's native promoter or introducing additional copies of the polynucleotide into the host cell.
As used herein, “polynucleotide” refers to a polymer composed of nucleotides. The polynucleotide may be in the form of a separate fragment or as a component of a larger nucleotide sequence construct, which has been derived from a nucleotide sequence isolated at least once in a quantity or concentration enabling identification, manipulation, and recovery of the sequence and its component nucleotide sequences by standard molecular biology methods, for example, using a cloning vector. When a nucleotide sequence is represented by a DNA sequence (i.e., A, T, G, C), this also includes an RNA sequence (i.e., A, U, G, C) in which “U” replaces “T.” Put another way, “polynucleotide” refers to a polymer of nucleotides removed from other nucleotides (a separate fragment or entity) or can be a component or element of a larger nucleotide construct, such as an expression vector or a polycistronic sequence. Polynucleotides include DNA, RNA and cDNA sequences.
As used herein, “polypeptide” refers to a polymer composed of amino acid residues which may or may not contain modifications such as phosphates and formyl groups.
As used herein, “recombinant expression vector” refers to a DNA construct used to express a polynucleotide that encodes a desired polypeptide. A recombinant expression vector can include, for example, a transcriptional subunit comprising (i) an assembly of genetic elements having a regulatory role in gene expression, for example, promoters and enhancers, (ii) a structural or coding sequence which is transcribed into mRNA and translated into protein, and (iii) appropriate transcription and translation initiation and termination sequences. Recombinant expression vectors are constructed in any suitable manner. The nature of the vector is not critical, and any vector may be used, including plasmid, virus, bacteriophage, and transposon. Possible vectors for use in the invention include, but are not limited to, chromosomal, nonchromosomal and synthetic DNA sequences, e.g., bacterial plasmids; phage DNA; yeast plasmids; and vectors derived from combinations of plasmids and phage DNA, DNA from viruses such as vaccinia, adenovirus, fowl pox, baculovirus, SV40, and pseudorabies.
As used herein, “primer” refers to a polynucleotide that is capable of specifically hybridizing to a designated polynucleotide template and providing a point of initiation for synthesis of a complementary polynucleotide when the polynucleotide primer is placed under conditions in which synthesis is induced.
As used herein, “recombinant polynucleotide” refers to a polynucleotide having sequences that are not naturally joined together. A recombinant polynucleotide may be included in a suitable vector, and the vector can be used to transform a suitable host cell. A host cell that comprises the recombinant polynucleotide is referred to as a “recombinant host cell.” The polynucleotide is then expressed in the recombinant host cell to produce, e.g., a “recombinant polypeptide.”
As used herein, “specific hybridization” refers to the binding, duplexing, or hybridizing of a polynucleotide preferentially to a particular nucleotide sequence under stringent conditions.
As used herein, “stringent conditions” refers to conditions under which a probe will hybridize preferentially to its target subsequence, and to a lesser extent to, or not at all to, other sequences.
As used herein, “short-chain fatty acids” refers to fatty acids having aliphatic tails with fewer than 6 carbons.
As used herein, “substantially homologous” or “substantially identical” in the context of two nucleic acids or polypeptides, generally refers to two or more sequences or subsequences that have at least 40%, 60%, 80%, 90%, 95%, 96%, 97%, 98% or 99% nucleotide or amino acid residue identity, when compared and aligned for maximum correspondence, as measured using sequence comparison algorithms or by visual inspection. The substantial identity can exist over any suitable region of the sequences, such as, for example, a region that is at least about 50 residues in length, a region that is at least about 100 residues, or a region that is at least about 150 residues. In certain embodiments, the sequences are substantially identical over the entire length of either or both comparison biopolymers.
In one embodiment, the invention relates to a novel method of producing scattered branched-chain fatty acids (or products derived from scattered branched-chain fatty acid) using bacteria. In general, the method includes increasing the supply of methylmalonyl-CoA and/or the conversion of methylmalonyl-CoA to methylmalonyl-ACP within the cell, incorporating the branch from the methylmalonyl-CoA into the fatty acid, and, optionally, using a thioesterase to specify the range of size of the fatty acids. In certain embodiments, the method provides branched-chain fatty acids having a chain length of C12 to C16. In addition, in certain embodiments, the branched-chain fatty acids have from about 0 to about 3 methyl branches, such as from about 1 to about 3 methyl branches, such as, for example, from about 1 to about 2 methyl branches, or 1, 2, or 3 methyl branches positioned on one or more carbons. In certain embodiments, the methyl branches are positioned on even-numbered carbons.
In one embodiment, scattered branched-chain fatty acid production is increased by increasing the production of methylmalonyl-CoA within the cell via, e.g., propionyl-CoA and/or succinyl-CoA intermediates. Thus, in one aspect, the invention provides a method for producing branched-chain fatty acid comprising a methyl on one or more even number carbons. The method comprises culturing a cell comprising an exogenous or overexpressed polynucleotide comprising a nucleic acid sequence encoding a polypeptide that catalyzes the conversion of propionyl-CoA to methylmalonyl-CoA and/or an exogenous or overexpressed polynucleotide comprising a nucleic acid sequence encoding a polypeptide that catalyzes the conversion of succinyl-CoA to methylmalonyl-CoA. The cell is cultured under conditions allowing expression of the polynucleotide(s) and production of the branched-chain fatty acid. The cell produces more branched-chain fatty acid comprising a methyl branch on one or more even number carbons than an otherwise similar cell that does not comprise the polynucleotide(s) (e.g., a cell of the same cell type or derived from the same organism that does not comprise the polynucleotide(s)). Propionyl-CoA is converted to methylmalonyl-CoA by, e.g., the action of a propionyl-CoA carboxylase. Any propionyl-CoA carboxylase that catalyzes the conversion of propionyl-CoA to methylmalonyl-CoA is suitable for use in the inventive method. An exemplary propionyl-CoA carboxylase is a carboxylase from Streptomyces coelicolor, which comprises two heterologous subunits encoded by pccB and by either accA1 or accA2. In certain embodiments, the cell of the inventive method is engineered to produce PccB and AccA1 or PccB and AccA2. In one aspect, the cell comprises one or more polynucleotides encoding polypeptide(s) comprising an amino acid sequence at least about 80% identical (e.g., 85%, 90%, 95%, or 100% identical) to the amino acid sequences set forth in SEQ ID NO: 9 and/or 10. Additional, non-limiting examples of polypeptides that catalyze the conversion of propionyl-CoA to methylmalonyl-CoA are propionyl-CoA carboxylases from Mycobacterium smegmatis, Homo sapiens, Acinetobacter baumannii, Brucella suis, Saccharopolyspora erythraea, Burkholderia glumae, and Aedes aegypti, as well as the propionyl-CoA carboxylases set forth in Table A.

TABLE A

	GenBank
Organism	Accession	Description	SEQ ID NO:

Ehrlichia chaffeensis	YP_507303	Propionyl-CoA carboxylase alpha subunit	51
		(PCCA)
Ehrlichia chaffeensis	YP_507410	Propionyl-CoA carboxylase beta subunit	52
		(PCCB)
Agrobacterium vitis	YP_002547482	Propionyl-CoA carboxylase alpha subunit	53
		(PCCA)
Agrobacterium vitis	YP_002547479	Propionyl-CoA carboxylase beta subunit	54
		(PCCB)
Methylobacterium	YP_003069256	Propionyl-CoA carboxylase alpha subunit	55
extorquens		(PCCA)
Methylobacterium	YP_003065890	Propionyl-CoA carboxylase beta subunit	56
extorquens		(PCCB)
Sinorhizobium meliloti	NP_437988	Propionyl-CoA carboxylase alpha subunit	57
		(PCCA)
Sinorhizobium meliloti	NP_437987	Propionyl-CoA carboxylase beta subunit	58
		(PCCB)
Ruegeria pomeroyi	YP_166352	Propionyl-CoA carboxylase alpha subunit	59
		(PCCA)
Ruegeria pomeroyi	YP_166345	Propionyl-CoA carboxylase beta subunit	60
		(PCCB)

Optionally, the cell is modified to increase carbon flow to propionyl-CoA (and then onward to methylmalonyl-CoA) by, for example, increasing expression of (i.e., overexpressing) prpE or other propionyl-CoA synthetase genes. Alternatively or in addition, an exogenous polynucleotide comprising a nucleic acid sequence encoding a propionyl-CoA synthetase is introduced into the host cell to upregulate propionyl-CoA production. Additionally, feeding host cells (e.g., microbes) large amounts of methionine, isoleucine, valine, threonine, propionic acid, and/or odd-chain length fatty acids (such as valeric acid) increases production of the propionyl-CoA precursor of methylmalonyl-CoA.
Methylmalonyl-CoA production via propionyl-CoA also is increased utilizing the metabolic pathway that converts pyruvate to propionyl-CoA, with lactate, lactoyl-CoA, and acrylyl-CoA as intermediates. Carbon flow to propionyl-CoA is upregulated by overproducing the enzymes of the pathway, producing exogenous enzymes catalyzing one or more conversions of the pathway, and/or by providing pyruvate or lactate in larger amounts than normally found in the host cell. For example, in any embodiment of the invention, the cell comprises an exogenous or overexpressed polynucleotide encoding lactate dehydrogenase, lactate CoA transferase, lactyl-CoA dehydratase, and/or acrylyl-CoA reductase.
In addition, in any aspect of the invention, carbon flow to branch pathways not contributing to formation of the desired branched-chain fatty acid is minimized by attenuation of endogenous enzyme activity responsible for the diversion of carbon. Complete abolishment of endogenous activity is not required; any reduction in activity is suitable in the context of the invention. Enzyme activity is attenuated (i.e., reduced or abolished) by, for example, mutating the coding sequence for the enzyme to create a non-functional or reduced-function polypeptide, by removing all or part of the coding sequence for the enzyme from the cellular genome, by interfering with translation of an RNA transcript encoding the enzyme (e.g., using antisense oligonucleotides), or by manipulating the expression control sequences influencing expression of the enzyme. For example, in one aspect, the cell is modified to prevent methylmalonyl-CoA degradation, thereby increasing the amount of methylmalonyl-CoA available for conversion to methylmalonyl-ACP. Methylmalonyl-CoA degradation is reduced by, for example, deleting or inactivating methylmalonyl-CoA decarboxylase from the host. Put another way, the cell is modified to attenuate endogenous methylmalonyl-CoA decarboxylase activity. In E. coli, for example, methylmalonyl-CoA decarboxylase activity is attenuated by, for example, deleting or mutating ygfG. Optionally, endogenous acyl transferase activity is attenuated. Alternatively or in addition, methylmalonyl-CoA production within the cell is increased by preventing alternative metabolism of propionyl-CoA to succinyl-CoA, such as, for example, by deleting or otherwise reducing (attenuating) the activity of an endogenous methylmalonyl-CoA mutase gene. Optionally, methylmalonyl-CoA levels are increased by increasing the degradation of valine directly to methylmalonyl-CoA. Valine degradation comprises the following intermediates: α-ketoisovalerate, isobutyryl-CoA, methacrylyl-CoA, β-hydroxyisobutyryl-CoA, β-hydroxyisobutyrate, and methylmalonate semialdehyde. Optionally, methylmalonate semialdehyde is converted directly to methylmalonyl-CoA or indirectly through a propionyl-CoA intermediate. In an exemplary embodiment, the cell of the invention comprises an overexpressed or exogenous polynucleotide comprising a nucleic acid sequence encoding one or more of the following enzymes: L-valine:2-oxoglutarate aminotransferase, 2-oxoisovalerate dehydrogenase, isobutyryl-CoA:FAD oxidoreductase, 3-hydroxy-isobutyryl-CoA hydro-lyase, 3-hydroxyisobutyryl-CoA hydrolase, 3-hydroxyisobutyrate dehydrogenase, and/or methylmalonate-semialdehyde dehydrogenase. Methylmalonate-semialdehyde dehydrogenase catalyzes the production of propanoyl-CoA, which can be converted to methylmalonyl-CoA by propanoyl-CoA carboxylase.
In one aspect, the cell comprises an exogenous or overexpressed polynucleotide comprising a nucleic acid sequence encoding a polypeptide that catalyzes the conversion of succinyl-CoA to methylmalonyl-CoA. An exemplary polypeptide that catalyzes the reaction is methylmalonyl-CoA mutase. In any embodiment of the invention, the cell is engineered to overexpress a methylmalonyl-CoA mutase gene, such as, for example, sbm (encoding Sleeping Beauty mutase) in E. coli. Alternatively or in addition, an exogenous polynucleotide comprising a nucleic acid sequence encoding a methylmalonyl-CoA mutase is expressed in the cell. Exemplary methylmalonyl-CoA mutases include, but are not limited to, Sbm from E. coli, MutA and/or MutB from Streptomyces cinnamonensis, and methylmalonyl-CoA mutases from Janibacter sp. HTCC2649, Corynebacterium glutamicum, Euglena gracilis, Homo sapiens, Propionibacterium shermanii, Bacillus megaterium, and Mycobacterium smegmatis. Additional, non-limiting examples of polypeptides that catalyze the conversion of succinyl-CoA to methylmalonyl-CoA are provided in Table B.

TABLE B

	GenBank
Organism	Accession	Description	SEQ ID NO.

Bacillus megaterium	YP_003564880	methylmalonyl-CoA mutase small subunit	61
		(mutA)
Bacillus megaterium	YP_003564879	methylmalonyl-CoA mutase large subunit	62
		(mutB)
Mycobacterium	YP_001282809	methylmalonyl-CoA mutase small subunit	63
tuberculosis		(mutA)
Mycobacterium	YP_001282810	methylmalonyl-CoA mutase large subunit	64
tuberculosis		(mutB)
Corynebacterium	YP_225814	methylmalonyl-COA mutase small subunit	65
glutamicum		(mutA)
Corynebacterium	YP_225813	methylmalonyl-CoA mutase large subunit	66
glutamicum		(mutB)
Rhodococcus	YP_002766535	methylmalonyl-CoA mutase small subunit	67
erythropolis		(mutA)
Rhodococcus	YP_002766536	methylmalonyl-CoA mutase large subunit	68
erythropolis		(mutB)
Porphyromonas	NP_905776	methylmalonyl-CoA mutase small subunit	69
gingivalis		(mutA)
Porphyromonas	NP_905777	methylmalonyl-CoA mutase large subunit	70
gingivalis		(mutB)

In one aspect, the cell comprises one or more polynucleotides encoding polypeptide(s) comprising an amino acid sequence at least about 80% identical (e.g., 85%, 90%, 95%, or 100% identical) to the amino acid sequences set forth in SEQ ID NO: 3, 4, and/or 28. The cell can comprise polynucleotides encoding a methylmalonyl-CoA mutase, a propionyl-CoA carboxylase, or both.
Depending on the substrate specificity of the fatty acid synthase produced by the cell, a methylmalonyl-CoA epimerase also may be desired to facilitate use of methylmalonyl-CoA as a precursor in fatty acid synthesis. Thus, in one aspect, the cell further comprises an exogenous or overexpressed polynucleotide comprising a nucleic acid sequence encoding a methylmalonyl-CoA epimerase. Methylmalonyl-CoA epimerases suitable for use in the invention include, but are not limited to, Sorangium cellulosum So ce 56 methylmalonyl-CoA epimerase, Streptomyces sviceus ATCC 29083 methylmalonyl-CoA epimerase, Kribbella flavida DSM 17836 methylmalonyl-CoA epimerase, and methylmalonyl-CoA epimerases from Homo sapiens, Bacillus megaterium, and Mycobacterium smegmatis.
Production of branched-chain fatty acid comprising a methyl branch on one or more even number carbons also is enhanced by upregulating conversion of methylmalonyl-CoA to methylmalonyl-ACP. In one or more embodiments, conversion of methylmalonyl-CoA to methylmalonyl-ACP is increased in the cell by engineering the cell to produce an acyl transferase (such as the acyl transferase encoded by fabD in E. coli) to catalyze the formation of methylmalonyl-ACP from methylmalonyl-CoA. Put another way, in one aspect, the cell further comprises an exogenous or overexpressed polynucleotide comprising a nucleic acid sequence encoding an acyl transferase. Any suitable acyl transferase can be used, such as, for example and without limitation, an acyl transferase domain from a polyketide synthase, such as those involved in the synthesis of monensin, epothilone, amphotericin, candicidin, nystatin, pimaricin, ascomycin, rapamycin, avermiectin, spinosad, mycinamicin, niddamycin, oleandomycin, megalomicin, nanchangmycin, picromycin, rifamycin, oligomycin erythromycin, polyenes, and macrolides, and an acyl transferase domain from Mycobacterium mycocerosic acid synthase. Acyl transferase domains from larger fatty acid synthase enzymes, such as Mycobacterium mycocerosic acid synthase, act upon methylmalonyl-CoA in the absence of other enzymatic domains of the larger synthase. Optionally, the acyl transferase lacks polyketide synthesis activity. By “polyketide synthesis activity” is meant enzymatic activity, other than acyl transferase activity, that catalyzes the production of polyketides in a host cell, such as, for example and without limitation, acyltransferase activity, ketoacyl synthase activity, ketoacyl reductase activity, dehydratase activity, enoyl reductase activity, acyl carrier protein activity, and thioesterase activity.
Alternatively, or in addition, in certain embodiments, a 3-ketoacyl-ACP synthase domain, such as, for example, a domain from a polyketide synthase or a mycocerosic acid synthase, is added to the fatty acid synthase of the host cell. In certain embodiments, the host cell (e.g., microbe) is engineered to include both acyl transferase and 3-ketoacyl-ACP synthase domains that can recognize methylmalonyl-CoA. In addition, in certain embodiments, genes for the endogenous acyl transferase and/or 3-ketoacyl-ACP synthase activities can be attenuated (e.g., deleted) to minimize the amount of malonyl-CoA incorporation in fatty acid synthesis.
In certain embodiments, the invention includes use of a thioesterase to specify the chain length of the fatty acid, such as, for example, to produce medium-chain fatty acids. In certain embodiments, the host cell further comprises an exogenous or overexpressed polynucleotide comprising a nucleic acid sequence encoding a thioesterase. In one aspect, the host cell (e.g., bacteria) is engineered to produce a thioesterase that assists in the production of medium-chain branched-chain fatty acids. Alternatively, the host cell is engineered to produce (or overproduce) a thioesterase that assists in the production of long-chain branched-chain fatty acids. Exemplary thioesterases include, for example, the mallard uropygial gland thioesterase, the California bay thioesterase, the rat mammary gland thioesterase II, E. coli TesA, the Cuphea wrightii thioesterase, and other thioesterases suitable for production of the desired chain-length fatty acids.
Optionally, the cell is modified to produce (or increase the production of) branched acyl-CoA, which is a substrate for elongase in the production of long chain fatty acid. In this regard, in an exemplary embodiment of the invention, the cell comprises an exogenous or overexpressed polynucleotide comprising a nucleic acid encoding a coenzyme-A synthetase, which converts branched-chain fatty acid to branched acyl-CoA. Examples of coenzyme-A synthetases include, but are not limited to, the coenzyme-A synthetase from Leishmania braziliensis (GenBank Accession No. XP_—001561614), and the coenzyme-A synthetase from Escherichia coli (GenBank Accession No. YP_—541006). Optionally, the cell comprises exogenous or overexpressed polynucleotide(s) comprising a nucleic acid sequence encoding an elongase to increase the length of the carbon backbone. Elongases are enzyme complexes that exhibit 3-ketoacyl-CoA synthase, 3-ketoacyl-CoA reductase, 3-hydroxyacyl-CoA dehydratase, and enoyl-CoA reductase activities, and generally utilize malonyl-CoA as an extension unit for extending the carbon chain. When a methyl-malonyl CoA is used as an extension unit by the enzyme complex, additional methyl branches are introduced at even carbon positions. Exemplary elongases include, but are not limited to, elongases comprising the one or more of the following subunits: Saccharomyces cerevisiae 3-ketoacyl-CoA synthase (GenBank Accession No. NP_—013476), 3-ketoacyl-CoA reductase (GenBank Accession No. NP_—009717), 3-hydroxyacyl-CoA dehydratase (GenBank Accession No. NP_—012438) and enoyl-CoA reductase (GenBank Accession No. NP_—010269); and Arabidopsis thaliana col 3-ketoacyl-CoA synthase (GenBank Accession No. NP_—849861), 3-ketoacyl-CoA reductase (GenBank Accession No. NP_—564905), 3-hydroxyacyl-CoA dehydratase (GenBank Accession No. NP_—193180), and enoyl-CoA reductase (GenBank Accession No. NP_—191096).
Any suitable cell or organism, such as, for example, bacterial cells and other prokaryotic cells, and yeast cells, can be used in the context of the invention. In one aspect, the invention relates to cells, such as Escherichia cells (e.g., E. coli), which naturally produce Type II fatty acid synthase and/or do not naturally produce scattered branched-chain fatty acid (i.e., branched-chain fatty acid comprising a methyl branch on one or more even numbered carbons). These cells are engineered to produce the branched-chain fatty acids as described herein. Alternatively, the cell naturally produces branched-chain fatty acid and is modified as described herein to produce higher levels of branched-chain fatty acid (or different proportions of different types of branched-chain fatty acid) compared to an unmodified cell. In certain embodiments, fatty acid is manufactured using bacteria known to make the methylmalonyl-CoA precursor, such as Streptomyces, Mycobacterium or Corynebacterium. These bacteria are, in one aspect, engineered to produce (i) an acyl transferase to increase carbon flux to methylmalonyl-ACP that is incorporated in the fatty acid synthesis pathway and/or (ii) a thioesterase to control the chain length.
Exemplary bacteria that are suitable for use in the invention include, but are not limited to, Spirochaeta aurantia, Spirochaeta littoralis, Pseudomonas maltophilia, Pseudomonas putrefaciens, Xanthomonas campestris, Legionella anisa, Moraxella catarrhalis, Thermus aquaticus, Flavobacterium aquatile, Bacteroides asaccharolyticus, Bacteroides fragilis, Succinimonas amylolytica, Desulfovibrio africanus, Micrococcus agilis, Stomatococcus mucilaginosus, Planococcus citreus, Marinococcus albusb, Staphylococcus aureus, Peptostreptococcus anaerobius, Ruminococcus albus, Sarcina lutea, Sporolactobacillus inulinus, Clostridium thermocellum, Sporosarcina ureae, Desulfotomaculum nigrificans, Listeria monocytogenes, Brochothrix thermosphacta, Renibacterium salmoninarum, Kurthia zopfii, Corynebacterium aquaticum, Arthrobacter radiotolerans, Brevibacterium fermentans, Propionibacterium acidipropionici, Eubacterium lentum, Cytophaga aquatilis, Sphingobacteriuma multivorumb, Capnocytophaga gingivalis, Sporocytophaga myxococcoides, Flexibacter elegans, Myxococcus coralloides, Archangium gephyra, Stigmatella aurantiaca, Oerskovia turbata, Escherichia coli, Bacillus subtilis, Salmonella typhimurium, Corynebacterium glutamicum, Streptomyces coelicolor, Streptomyces lividans, Clostridium thermocellum and Saccharomonospora viridis.
In one aspect, the fatty acid produced by the inventive cell comprises about 80% to about 100% (wt.) (e.g., about 85%, about 90%, or about 95%) linear and branched-chain fatty acid. Of the linear and branched-chain fatty acids produced by the cell, approximately 1% to approximately 95% or more (e.g., 5%, 10%, 15%, 20%, 30%, 50%, 60%, 75%, 85%, or 100%) is branched-chain fatty acid comprising a methyl group on one or more even carbons. In some embodiments, the cell does not produce, or produces only trace amounts of, fatty acid comprising methyl branching on odd numbered carbons. By “trace amount” is meant less than 1% of the total fatty acid content produced by the cell. Alternatively or in addition, in one aspect, the mixture of fatty acids produced by the cell comprises no more than 50% end-terminal-branched fatty acid (i.e., fatty acids that contain branching on a carbon atom that is within 40% of the non-functionalized terminus of the longest carbon chain). Optionally, the inventive cell is modified to preferentially produce branched-chain fatty acid with desired chain lengths, e.g., about six to about 18 carbons or more in the carbon backbone (not including the methyl branch(es)). In some embodiments, the host cell preferentially generates long chain fatty acid, medium-length chain fatty acid, short chain fatty acid, or a desired combination fatty acids (e.g., 60%, 70%, 80%, 85%, 90%, 95% or more of the branched-chain fatty acid produced by the cell comprises the desired number of carbons). In addition, in certain embodiments, the engineered cells tolerate large amounts of branched-chain fatty acid in the growth medium, plasma membrane, or lipid droplets, and/or produce branched-chain fatty acid more economically than an unmodified cell by, e.g., using a less expensive feedstock, requiring less fermentation time, and the like.
The polynucleotide(s) encoding one or more polypeptides that catalyze the reaction(s) for producing branched-chain fatty acid may be derived from any source. Depending on the embodiment of the invention, the polynucleotide is isolated from a natural source such as bacteria, algae, fungi, plants, or animals; produced via a semi-synthetic route (e.g., the nucleic acid sequence of a polynucleotide is codon-optimized for expression in a particular host cell, such as E. coli); or synthesized de novo. In certain embodiments, it is advantageous to select an enzyme from a particular source based on, e.g., the substrate specificity of the enzyme, the type of branched-chain fatty acid produced by the source, or the level of enzyme activity in a given host cell. In one aspect of the invention, the enzyme and corresponding polynucleotide are naturally found in the host cell and overexpression of the polynucleotide is desired. In this regard, in some instances, additional copies of the polynucleotide are introduced in the host cell to increase the amount of enzyme available for fatty acid production. Overexpression of a native polynucleotide also is achieved by upregulating endogenous promoter activity, or operably linking the polynucleotide to a more robust promoter. Exogenous enzymes and their corresponding polynucleotides also are suitable for use in the context of the invention, and the features of the biosynthesis pathway or end product can be tailored depending on the particular enzyme used. If desired, the polynucleotide(s) is isolated or derived from the branched-chain fatty acid-producing organisms described herein.
In certain embodiments, the cell produces an analog or variant of a polypeptide described herein. Amino acid sequence variants of the polypeptide include substitution, insertion, or deletion variants, and variants may be substantially homologous or substantially identical to the unmodified polypeptides as set out above. In certain embodiments, the variants retain at least some of the biological activity, e.g., catalytic activity, of the polypeptide. Other variants include variants of the polypeptide that retain at least about 50%, preferably at least about 75%, more preferably at least about 90%, of the biological activity.
Substitution variants typically exchange one amino acid for another at one or more sites within the protein. Substitutions of this kind can be conservative, that is, one amino acid is replaced with one of similar shape and charge. Conservative substitutions include, for example, the changes of: alanine to serine; arginine to lysine; asparagine to glutamine; aspartate to glutamate; cysteine to serine; glutamine to asparagine; glutamate to aspartate; isoleucine to leucine or valine; leucine to valine or isoleucine; lysine to arginine; methionine to leucine or isoleucine; phenylalanine to tyrosine, leucine or methionine; serine to threonine; threonine to serine; tryptophan to tyrosine; tyrosine to tryptophan or phenylalanine; and valine to isoleucine or leucine.
In some instances, the recombinant cell comprises an analog or variant of the exogenous or overexpressed polynucleotide(s) described herein. Nucleic acid sequence variants include one or more substitutions, insertions, or deletions, and variants may be substantially homologous or substantially identical to the unmodified polynucleotide. Polynucleotide variants or analogs encode mutant enzymes having at least partial activity of the unmodified enzyme. Alternatively, polynucleotide variants or analogs encode the same amino acid sequence as the unmodified polynucleotide. Codon-optimized sequences, for example, generally encode the same amino acid sequence as the parent/native sequence but contain codons that are preferentially expressed in a particular host organism.
A polypeptide or polynucleotide “derived from” an organism contains one or more modifications to the native amino acid sequence or nucleotide sequence and exhibits similar, if not better, activity compared to the native enzyme (e.g., at least 70%, at least 80%, at least 90%, at least 95%, at least 100%, or at least 110% the level of activity of the native enzyme). For example, enzyme activity is improved in some contexts by directed evolution of a parent/native sequence. Additionally or alternatively, an enzyme coding sequence is mutated to achieve feedback resistance. Thus, in one or more embodiments of the invention, the polypeptide encoded by the exogenous polynucleotide is feedback resistant and/or is modified to alter the activity of the native enzyme. A polynucleotide “derived from” a reference polynucleotide encompasses, but is not limited to, a polynucleotide comprising a nucleic acid sequence that has been codon-optimized for expression in a desired host cell.
The cell of the invention may comprise any combination of polynucleotides described herein to produce branched-chain fatty acid comprising a methyl branch on one or more even number carbons. For example, the invention provides a cell comprising (i) an exogenous or overexpressed polynucleotide comprising a nucleic acid sequence encoding an acyl transferase lacking polyketide synthesis activity, and (ii) an exogenous or overexpressed polynucleotide comprising a nucleic acid sequence encoding a propionyl-CoA carboxylase and/or an exogenous or overexpressed polynucleotide comprising a nucleic acid sequence encoding a methylmalonyl-CoA mutase, wherein the polynucleotide(s) are expressed and the cell produces more branched-chain fatty acid comprising a methyl on one or more even number carbons than an otherwise similar cell that does not comprise the polynucleotide(s). Recombinant cells can be produced in any suitable manner to establish an expression vector within the cell. The expression vector can include the exogenous polynucleotide operably linked to expression elements, such as, for example, promoters, enhancers, ribosome binding sites, operators and activating sequences. Such expression elements may be regulatable, for example, inducible (via the addition of an inducer). Alternatively or in addition, the expression vector can include additional copies of a polynucleotide encoding a native gene product operably linked to expression elements. Representative examples of useful promoters include, but are not limited to: the LTR (long terminal 35 repeat from a retrovirus) or SV40 promoter, the E. coli lac, tet, or trp promoter, the phage Lambda P_Lpromoter, and other promoters known to control expression of genes in prokaryotic or eukaryotic cells or their viruses. In one aspect, the expression vector also includes appropriate sequences for amplifying expression. The expression vector can comprise elements to facilitate incorporation of polynucleotides into the cellular genome. Introduction of the expression vector or other polynucleotides into cells can be performed using any suitable method, such as, for example, transformation, electroporation, microinjection, microprojectile bombardment, calcium phosphate precipitation, modified calcium phosphate precipitation, cationic lipid treatment, photoporation, fusion methodologies, receptor mediated transfer, or polybrene precipitation. Alternatively, the expression vector or other polynucleotides can be introduced by infection with a viral vector, by conjugation, by transduction, or by other any other suitable method.
Cells, such as bacterial cells, containing the polynucleotides encoding the proteins described herein can be cultured under conditions appropriate for growth of the cells and expression of the polynucleotides. Cells expressing the protein can be identified by any suitable methods, such as, for example, by PCR screening, screening by Southern blot analysis, or screening for the expression of the protein. In certain embodiments, cells that contain the polynucleotide(s) can be selected by including a selectable marker in the DNA construct, with subsequent culturing of cells containing a selectable marker gene, under conditions appropriate for survival of only those cells that express the selectable marker gene. The introduced DNA construct can be further amplified by culturing genetically modified cells under appropriate conditions (e.g., culturing genetically modified cells containing an amplifiable marker gene in the presence of a concentration of a drug at which only cells containing multiple copies of the amplifiable marker gene can survive). Cells that contain and express polynucleotides encoding the exogenous proteins can be referred to herein as genetically modified cells. Bacterial cells that contain and express polynucleotides encoding the exogenous protein can be referred to as genetically modified bacterial cells.
Exemplary cells of the invention include E. coli BW25113 comprising pTrcHisA mmat and pZA31-accA1-pccB, which was deposited with American Type Culture Collection (ATCC), 10801 University Blvd., Manassas, Va., on Dec. 14, 2010, under the provisions of the Budapest Treaty for the International Recognition of the Deposit of Microorganisms for the Purpose of Patent Procedure (“Budapest Treaty”), and assigned Deposit Accession No. [XXX] on [DATE], and E. coli BL21 Star (DE3) comprising pTrcHisA Ec sbm So ce epi and pZA31 mmat which was deposited with American Type Culture Collection (ATCC), 10801 University Blvd., Manassas, Va., on Dec. 14, 2010, under the provisions of the Budapest Treaty for the International Recognition of the Deposit of Microorganisms for the Purpose of Patent Procedure (“Budapest Treaty”), and assigned Deposit Accession No. [XXX] on [DATE]. The invention also includes variants or progeny of the cells described herein that retain the phenotypic characteristics of the recombinant microbe. A substantially pure monoculture of the cell described herein (i.e., a culture comprising at least 80% or at least 90% of a desired cell) also is provided.
Any cell culture conditions appropriate for growing a host cell and synthesizing branched-chain fatty acid is suitable for use in the inventive method. Addition of fatty acid synthesis intermediates, precursors, and/or co-factors for the enzymes associated with branched-chain fatty acid synthesis to the culture is contemplated herein. In certain embodiments, the genetically modified cells (such as genetically modified bacterial cells) have an optimal temperature for growth, such as, for example, a lower temperature than normally encountered for growth and/or fermentation. For example, in certain embodiments, incorporation of branched-chain fatty acids into the membrane may increase membrane fluidity, a property normally associated with low growth temperatures. In addition, in certain embodiments, cells of the invention may exhibit a decline in growth at higher temperatures as compared to normal growth and/or fermentation temperatures as typically found in cells of the type.
The inventive method optionally comprises extracting branched-chain fatty acid from the culture. Fatty acids can be extracted from the culture medium and measured using any suitable manner. Suitable extraction methods include, for example, methods as described in: Bligh et al., A rapid method for total lipid extraction and purification, Can. J. Biochem. Physiol. 37:911-917 (1959). In certain embodiments, production of fatty acids in the culture supernatant or in the membrane fraction of recombinant cells can be measured. In this embodiment, cultures are prepared in the standard manner, although nutrients (e.g., 2-methylbutyrate, isoleucine) that may provide a boost in substrate supply can be added to the culture. Cells are harvested by centrifugation, acidified with hydrochloric or perchloric acid, and extracted with chloroform and methanol, with the fatty acids entering the organic layer. The fatty acids are converted to methyl esters, using methanol at 100° C. The methyl esters are separated by gas chromatography (GC) and compared with known standards of fatty acids (purchased from Larodan or Sigma). Confirmation of chemical identity is carried out by combined GC/mass spec, with further mass spec analysis of fragmented material carried out if necessary.
In one embodiment, the cell utilizes the branched-chain fatty acid as a precursor to make one or more other products. Products biosynthesized (i.e., derived) from branched-chain fatty acid include, but are not limited to, phospholipids, triglycerides, alkanes, olefins, wax esters, fatty alcohols, and fatty aldehydes. Some host cells naturally generate one or more products derived from branched-chain fatty acid; other host cells are genetically engineered to convert branched-chain fatty acid to, e.g., an alkane, olefin, wax ester, fatty alcohol, phospholipid, triglyceride, and/or fatty aldehyde. Organisms and genetic modifications thereof to synthesize products derived from branched-chain fatty acids are further described in, e.g., International Patent Publication Nos. WO 2007/136762, WO 2008/151149, and WO 2010/062480, and U.S. Patent Application Publication US 2010/0298612, all of which are hereby incorporated by reference in their entirety. In one aspect, the inventive method comprises extracting a product derived from branched-chain fatty acid (phospholipid, triglyceride, alkane, olefin, wax ester, fatty alcohol, and/or fatty aldehyde synthesized in the cell from branched-chain fatty acid) from the culture. Any extraction method is appropriate, including the extraction methods described in International Patent Publication Nos. WO 2007/136762, WO 2008/151149, and WO 2010/062480, and U.S. Patent Application Publication Nos. US 2010/0251601, US 20100242345, US 20100105963, and US 2010/0298612.
The inventive cell preferably produces more branched-chain fatty acid comprising a methyl branch on one or more even number carbons than an otherwise similar cell that does not comprise the polynucleotide(s). Methods of measuring fatty acid released into the fermentation broth or culture media or liberated from cellular fractions are described herein. Branched-chain fatty acid production is not limited to fatty acid accumulated in the culture, however, but also includes fatty acid used as a precursor for downstream reactions yielding products derived from branched-chain fatty acid. Thus, products derived from branched-chain fatty acid (e.g., phospholipids, triglycerides, fatty alcohols, olefins, wax esters, fatty aldehydes, and alkanes) are, in some embodiments, surrogates for measuring branched-chain fatty acid production in a host cell. Methods of measuring fatty acid content in phospholipid in the cell membrane are described herein. Similarly, measurement of degradation products of branched-chain fatty acids also is instructive as to the amount of branched-chain fatty acid is produced in a host cell. Depending on the particular embodiment of the invention, the inventive cell produces at least 3%, at least 5%, at least 10%, at least 20%, at least 25%, or at least 50% more branched-chain fatty acid than an otherwise similar cell that does not comprise the polynucleotide(s).
The invention further provides a composition comprising the branched-chain fatty acids described herein. For example, the invention provides a composition comprising a branched-chain fatty acid comprising between 10-18 carbons in the carbon backbone, such as fatty acids comprising between 10 and 16 carbons (e.g., fatty acids comprising 10, 11, 12, 13, 14, 15, or 16 carbons), with branching on one or more even numbered carbons (e.g., C2, C4, C6, C8, C10, C12, C14, and/or C16). A composition comprising longer-chain fatty acid also is provided, such as a composition comprising between 19 and 22 carbons in the longest carbon chain. A composition comprising a combination of any of the fatty acids described herein also is provided (e.g., a composition comprising fatty acids of varying lengths and/or branch locations along the carbon backbone).
The following examples further describe and demonstrate embodiments within the scope of the invention. The examples are given solely for the purpose of illustration and are not to be construed as limitations of the invention, as many variations thereof are possible without departing from the spirit and scope of the invention.

Example 1

Construction of Methylmalonyl-CoA Mutase Expression Vector

There are numerous genes annotated to encode the two subunits of methylmalonyl-CoA mutase. Janibacter sp. HTCC2649 encodes two such genes. Synthetic versions of these genes were prepared, with the codon usage altered to match that used by many E. coli genes (i.e., the coding sequence was codon-optimized for expression in E. coli). By analogy to other methylmalonyl-CoA mutase genes, these synthetic genes were named mutA (SEQ ID NO: 1) and mutB (SEQ ID NO: 2), corresponding to the MutA (SEQ ID NO: 3) and MutB (SEQ ID NO: 4) protein subunits. In the synthetic DNA, an extra three base pairs were added (encoding an alanine residue immediately after the initiation methionine) in mutA to facilitate introduction of an NcoI site. An XhoI restriction site was also placed after the coding sequence of mutB for insertion into the pBAD vector (Invitrogen). The NcoI/XhoI fragment was cloned into pBAD.

Example 2

Construction of Methylmalonyl-CoA Epimerase Expression Vector

There are numerous genes annotated to encode methylmalonyl-CoA mutase. One such gene is from Streptomyces sviceus. A synthetic gene can be constructed (SEQ ID NO: 5) using codon usage similar to E. coli genes and with EcoRI and Hind III sites flanking the coding region. An E. coli Shine-Dalgarno sequence can be added between the EcoRI site and the initiation codon for the epimerase gene. The predicted protein product is the same as the predicted protein product from the S. sviceus gene (SEQ ID NO: 6). The epimerase gene can be cloned into the pBAD-mutAB construct using the EcoRI and Hind III restriction sites (downstream of mutB) to form the pBAD-mutAB-epimerase gene plasmid. E. coli cultures can be grown at 27° C. after induction with arabinose and supplemented with hydroxycobalamin to achieve expression of functional methylmalonyl-CoA mutase and branched-chain fatty acid production.

Example 3

Construction of Propionyl-CoA Carboxylase Expression Vector

Nucleotide sequences (SEQ ID NO: 7 and SEQ ID NO: 8) encoding the two propionyl-CoA carboxylase subunits AccA1 (GenBank Accession NO. AF113603.1; SEQ ID NO: 9) and PccB (GenBank Accession No. AF113605.1; SEQ ID NO: 10)), respectively, from the Streptomyces coelicolor A3(2) propionyl-CoA carboxylase (Rodriguez E., Gramajo H., Microbiology. 1999 November; 145:3109-19), were codon-optimized for E. coli expression. A gene construct for expressing propionyl-CoA carboxylase was constructed with the following elements sequentially 1) P_Llac0-1promoter and operator plus T7 gene10 ribosomal binding site (SEQ ID NO: 11); 2) optimized accA1 (SEQ ID NO: 12); 3) three restriction site sequences including BglII, NotI and XbaI and a T7 gene10 ribosome binding site (SEQ ID NO: 13); and 4) codon-optimized pccB (SEQ ID NO: 14). The synthesized DNA fragments were cloned into the XhoI and PstI sites of expression vector pZA31-MCS (Expressys, Ruelzheim, Germany), resulting in plasmid pZA31-accA1-pccB (SEQ ID NO: 15).

Example 4

Construction of Propionyl-CoA Synthetase Expression Vector

The Salmonella enterica propionyl-CoA synthetase gene, prpE, was amplified using PCR and the primers set forth in SEQ ID NO: 16 and SEQ ID NO: 17, and placed behind a Shine-Dalgarno sequence in the plasmid pZA31-accA1-pccB (SEQ ID NO: 15) using the restriction enzymes PstI and BamHI. Enhanced propionyl-CoA synthetase production is expected to increase synthetic flux to propionyl-CoA.

Example 5

Reduction of Propionylation of Propionyl-CoA Synthetase

In S. enterica, propionyl-CoA synthetase is subject to inhibition by propionylation at lysine 592 when propionyl-CoA levels accumulate. (Garrity et al, J. Biol. Chem., Vol. 282, Issue 41, 30239-30245, Oct. 12, 2007). Similar enzyme modulation may occur in other species, although the position of the modified lysine may be different. Several strategies to overcome this inhibition will be tested and compared. First, the propionyl-CoA synthetase gene will be mutated to change the coding capacity from lysine (at the site of propionylation) to arginine or other amino acids to prevent propionylation. Second, a source of resveratrol or other sirtuin activators will be introduced into the culture medium to activate sirtuin to depropionylate PrpE. Third, the endogenous N-acetyltransferase enzyme responsible for the propionylation reaction will be knocked out. For example, if working with S. enterica, pat could be deleted. As another example, if working with B. subtilis, acuA could be deleted. Fourth, the flux of propionyl-CoA into fatty acid synthesis will be increased by increasing propionyl-CoA carboxylase activity to keep free propionyl-CoA levels down. Fifth, the sirtuin activity will be increased, thus increasing deacetylation of propionyl-CoA carboxylase. For example, the S. enterica cobB expression could be increased.

Example 6

Creation of an Expression Vector Comprising the Coding Sequence of the MMAT (Methylmalonyl-CoA Acyl Transferase) Domain from Mycobacterium Mycocerosic Acid Synthase (MAS).

Mycobacterium MAS is a multifunctional protein that catalyzes the synthesis of mycocerosic acid and that contains a domain with MMAT activity. The MMAT domain (amino acids 508-890) (SEQ ID NO: 18) of MAS from Mycobacterium bovis BCG (YP_—979046) (SEQ ID NO: 19) was codon optimized for E. coli expression (SEQ ID NO: 20). The optimized sequence was synthesized and cloned into vector pTrcHisA (Invitrogen) between the BamHI and HindIII sites. The resulting construct fused the MMAT domain with the His tag leader peptide encoded by the vector. The expression vector was introduced into a recombinant E. coli host that produces methylmalonyl-CoA. MMAT activity catalyzes the formation of methylmalonyl-ACP, which subsequently can be incorporated into the type II fatty acid synthesis pathway to form methyl branches at even positions of the fatty acid chain.

Example 7

Method for Detecting Acyl-CoA

This example describes an exemplary method for detecting and quantifying an acyl-CoA (e.g., methylmalonyl-CoA) in a sample, such as a sample of recombinant host cells producing branched-chain fatty acid.
A stable, labeled (deuterium) internal standard-containing master mix was prepared comprising d₃-3-hydroxymethylglutaryl-CoA (200 μl of 50 μg/ml stock in 10 ml of 15% trichloroacetic acid). An aliquot (500 μl) of the master mix was added to a 2 ml tube. Silicone oil (AR200; Sigma catalog number 85419; 800 μl) was layered onto the master mix. An E. coli culture (800 μl) was layered gently on top of the silicone oil, and the resulting sample was subjected to centrifugation at 20,000×g for five minutes at 4° C. in an Eppendorf 5417 C centrifuge. A portion (300 μl) of the master mix-containing layer was transferred to an empty tube and frozen on dry ice for 30 minutes.
The acyl-CoA content of samples was determined using HPLC/MS/MS. Individual coenzyme-A standards (propionyl-CoA, methylmalonyl-CoA, succinyl-CoA, malonyl-CoA, isobutyryl-CoA, isovaleryl-CoA, and acetyl-CoA) were purchased from Sigma Chemical Company (St. Louis, Mo.) and prepared as 500 μg/ml stocks in methanol. The analytes were pooled, and standards with all of the analytes were prepared by dilution with 15% trichloroacetic acid. Standards for regression were prepared by transferring 500 μl of the working standards to an autosampler vial containing 10 μL of the 50 μg/ml internal standard. Sample peak areas (or heights) were normalized to the stable-labeled internal standard (d₃-3-hydroxymethylglutaryl-CoA, Cayman Chemical Co.). Samples were assayed by HPLC/MS/MS on a Sciex API5000 mass spectrometer in positive ion Turbo Ion Spray. Separation was carried out by reversed-phase high performance liquid chromatography using a Phenomenex Onyx Monolithic C18 column (2×50 mm) and mobile phases of (1) 5 mM ammonium acetate, 5 mM dimethylbutylamine, 6.5 mM acetic acid and (2) acetonitrile with 0.1% formic acid, with the gradient set forth in Table C.

TABLE C

	Mobile	Mobile
	Phase A	Phase B
Time	(%)	(%)

0 min	97.5	2.5
1.0 min	97.5	2.5
2.5 min	91.0	9.0
5.5 min	45	55
6.0 min	45	55
6.1 min	97.5	2.5
7.5 min	—	—
9.5 min	End Run

The conditions on the mass spectrometer were: DP 160, CUR 30, GS1 65, GS2 65, IS 4500, CAD 7, TEMP 650 C. The transitions set forth in Table D were used for the multiple reaction monitoring (MRM).

TABLE D

	Precursor	Product	Collision
Compound	Ion*	Ion*	Energy	CXP

n-Propionyl-CoA	824.3	317.2	41	32
Methylmalonyl-CoA	868.1	317.1	42	31
Succinyl-CoA	868.2	361.1	49	38
Malonyl-CoA	854.2	347.2	41	36
Isobutyryl-CoA	838.3	345.2	45	34
Isovaleryl-CoA	852.2	345.2	45	34
Acetyl-CoA	810.3	303.2	43	30
d3-3-Hydroxymethylglutaryl-	915.2	408.2	49	13
CoA

*Energy (Volts) for MS/MS analysis

Example 8

Analysis of Fatty Acids Produced by Host Cells

This example illustrates a method of analyzing branched-chain fatty acids produced by cells (e.g., recombinant microbes).
Cell cultures (approximately 1.5 ml) were frozen in 2.0 ml glass vials and stored at −20° C. until ready for processing. Samples were chilled on dry ice for 30 minutes and lyophilized overnight (−16 hours) until dry. A 10 μl aliquot of internal standard (glyceryl trinonadecanoate (Sigma catalog number T4632-1G)) was added to each vial, followed by 400 μL of 0.5 N NaOH (in methanol). The vial was capped and vortexed for 10 seconds. Samples were incubated at 65°C. for 30-50 minutes. Samples were then removed from the incubator, and 500 μl of boron trifluoride reagent (Aldrich catalog number B1252) was added. The samples were vortexed again for 10 seconds, incubated at 65° C. for 10-15 minutes, and cooled to room temperature (approximately 20 minutes). Hexane (350 μl) was added, and the samples were again vortexed for 10 seconds. If the phases did not separate, 50-100 μl of saturated salt solution (5 g NaCl to 5 ml water) was added, and the sample was vortexed for 10 seconds. At least 100 μl of the top hexane layer was placed into the gas chromatography vial. The vial was capped and stored at 4° C. until analyzed by gas chromatography.
Gas chromatography was performed as described in Table E below. A bacterial acid methyl ester standard (Sigma catalog number 47080-U) and a fatty acid methyl ester standard (Sigma catalog number 47885-U) were used to identify peaks in samples. A sample check standard using glyceryl tripalmitate (Sigma catalog number T5888-1G) was used to confirm esterification of samples. A blank standard (internal standard only) was used to assess background noise.

TABLE E

Gas Chromatograph	HP 5890 GC Series II
Detector	FID 360° C. 40 ml/min Hydrogen,
	400 ml/min Air
Carrier Gas	Helium
Quantitative	GC Chemstation A.09.03. (Agilent)
Program
Column	VF-5 ms 15 M × 0.150 mm × 0.15 μm
	Varian catalog number CP9035
Injection Liner	Gooseneck (with glass wool packing)
Injector	HP 7673
Injection Syringe	10 μL
Injection Mode	Split 25:1
Injection volume	4 μL (Plunger Speed = fast; 5 sample pumps)
Pre Injection Solvent	2 samples
Washes
Post Injection	3 for both acetone and hexane
Solvent Washes
Injector Temperature	325° C.
Total Program Time	16 minutes

	Initial	Initial		Final	Final
	Temp.	Time	Rate	Temp	Time
	(° C.)	(min)	(° C./min)	(° C.)	(min)

Thermal Program	90	0.75	20.0	325	1.0
			25.0	350	2.5

Example 9

Construction of Expression Vectors Comprising S. Cinnamonensis mutA and mutB and S. sviceus epi.

A synthetic DNA construct was generated comprising Streptomyces cinnamonensis mutA (SEQ ID NO: 24) (GenBank Accession No. AAA03040.1), S. cinnamonensis mutB (SEQ ID NO: 25) (GenBank Accession No. AAA03041.1), and a Streptomyces sviceus ATCC 29083 methylmalonyl-CoA epimerase gene (SEQ ID NO: 26) (GenBank Accession No. ZP_—06919825.1). The genes were codon-optimized for expression in E. coli. An EcoRI restriction site was placed on the 5′ end, and a BamHI site was placed on the 3′ end of the synthesized gene construct. These sites were subsequently used for cloning into a pZA31 vector (Expressys, Ruelzheim, Germany). A ribosome binding sequence and spacer was placed before the mutA and epimerase gene start codons (SEQ ID NO: 27). The plasmid was designated pZA31 mutAB Ss epi.

Example 10

Construction of Expression Vectors Comprising Sbm and malE/sbm Polynucleotides

Sleeping beauty mutase (Sbm) (also known as methylmalonyl-CoA mutase (MCM)) is an enzyme that catalyzes the rearrangement of succinyl-CoA to L-methylmalonyl-CoA. The enzyme is vitamin B12 (cobalamin) dependent. Methylmalonyl-CoA is a building block for scattered branch-chain fatty acids (sBCFA) (i.e., branched-chain fatty acid comprising a methyl branch on one or more even number carbons of the fatty acid backbone). Plasmids comprising a polynucleotide encoding Sbm were generated to introduce multiple copies of the Sbm coding sequence, downstream of a regulatable promoter, into E. coli host cells.
A polynucleotide was synthesized based on the sequence of E. coli sbm (SEQ ID NO: 28) (GenBank Accession No. NP_—417392.1) from E. coli strain MG1655. The nucleic acid sequence was codon-optimized to match the pattern of highly expressed E. coli genes while maintaining the native amino acid sequence of the enzyme. The generated nucleic acid sequence is set forth in SEQ ID NO: 29. A BamHI and an XbaI site were added at the 5′ end of the synthetic Sbm coding sequence with the sequence GGATCCATGTCTAGA (SEQ ID NO: 49) adjacent to the ATG translation initiation sequence. A SacI restriction site sequence was added to the 3′ end of the synthetic Sbm coding sequence. The gene was synthesized, cloned into a pUC57 vector, and sequenced (GenScript, Piscataway, N.J.). The synthetic sbm was then released from pUC57 by restriction enzymes BamHI and Sad, and sub-cloned into plasmid pTrcHisA (Invitrogen, Carlsbad, Calif.) in frame with the poly-histidine sequence (GenScript, Piscataway, N.J.). The plasmid was designated pTrcHisA Ec sbm. The sequence was confirmed by sequencing (GenScript, Piscataway, N.J.). The recombinant protein encoded by the sequence contained a poly-histidine sequence (Met-Gly-Gly-Ser-His-His-His-His-His-His-Gly-Met-Ala-Ser-Met-Thr-Gly-Gly-Gln-Gln-Met-Gly-Arg-Thr-Asp-Asp-Asp-Asp-Lys-Asp-Arg-Trp-Gly-Ser (SEQ ID NO: 50)) and a full-length native Sbm amino acid sequence.
A recombinant methylmalonyl-CoA mutase has been reported to be insoluble in E. coli (Korotkova, N., and M. E. Lidstrom. J. Biological Chemistry 279: 13652-8 (2004)). Translation fusion with maltose-binding protein (MBP, encoded by malE) prevents aggregation of recombinant proteins (Kapust, R. B., and D. S. Waugh. Protein Science 8: 1668-74 (1999)). A recombinant construct was generated by inserting malE upstream of sbm. The malE polynucleotide was synthesized based on the sequence of maltose binding protein (E. coli MG1655 GenBank NC_—000913.2 (GenScript, Piscataway, N.J.)). A BamHI site was placed adjacent to the translation initiation codon of malE, and an XbaI site was placed immediately 5′ to the stop codon of the malE sequence (SEQ ID NO: 30). Also, one nucleotide was changed (T438 to C438) to remove a restriction site recognition sequence for BglII.
The MalE coding sequence (SEQ ID NO: 30) was first synthesized and cloned into a pUC57 plasmid. After confirming its sequence, the malE polynucleotide was released using restriction enzymes BamHI and XbaI. The released malE was then re-cloned into plasmid pTrcHisA Ec sbm at BamHI and XbaI sites (GenScript, Piscataway, N.J.). The resulting plasmid was designated pTrcHisA Ec malE Ec sbm. The recombinant protein encoded by pTrcHisA Ec malE Ec sbm contains three peptides: the poly-histidine tag, full-length MBP, and full-length Sbm.

Example 11

Construction of a Recombinant Expression Vector Comprising a Polynucleotide Encoding the Methylmalonyl-CoA Acyl Transferase (MMAT) Domain from Mycobacterium Mycocerosic Acid Synthase (MAS).

Mycobacterium MAS is a multifunctional protein containing MMAT activity that catalyzes the synthesis of mycocerosic acid. The nucleic acid sequence encoding the MMAT domain (amino acids 508-890) (SEQ ID NO: 18) of MAS from Mycobacterium bovis BCG (GenBank Accession No. YP_—979046) (SEQ ID NO: 19) was codon-optimized for E. coli expression (SEQ ID NO: 20). The optimized sequence, designated “mmat,” was synthesized and cloned into vector pTrcHisA (Invitrogen) between the BamHI and HindIII sites. The resulting construct fused the MMAT domain with the poly-histidine tag encoded by the vector. The expression vector (pTrcHisA mmat) was introduced into a recombinant E. coli host that produces methylmalonyl-CoA. MMAT activity catalyzes the formation of methylmalonyl-ACP, which is incorporated by Type II fatty acid synthase into fatty acid, forming methyl branches at even positions of the fatty acid chain.
An expression vector encoding Mycobacterium bovis BCG fused to a poly-histidine tag also was generated. The pTrcHisA mmat plasmid DNA described above was amplified by PCR using oligonucleotides synthesized to include 5′-KpnI (SEQ ID NO: 31) and 3′-HindIII restriction sites (SEQ ID NO: 32) (Integrated DNA Technologies, Inc., Coralville, Iowa). PCR was run on samples having 1 μl (2 ng) pTrcHisA mmat DNA, 1.5 μl of a 10 μM stock of each primer, 5 μl of 10× Pfx reaction mix (Invitrogen Carlsbad, Calif.), 0.5 μl of Pfx DNA polymerase (1.25 units), and 41 μl of water. PCR conditions were as follows: the samples were initially incubated at 95° C. for three minutes, followed by 30 cycles at 95° C. for 30 seconds (strand separation), 58° C. for 30 seconds (primer annealing), and 68° C. primer extension for 1.5 minutes. Following the cycles, the samples were incubated for 10 minutes at 68° C., and the samples were then held at 4° C.
The PCR products were purified using a QIAquick® PCR Purification Kit (Qiagen), digested with restriction enzymes KpnI and HindIII and ligated (Fast-Link Epicentre Biotechnologies, Madison, Wis.) with KpnI/HindIII-digested pZA31MCS (Expressys, Ruelzheim, Germany). The ligation mix was used to transform E. coli DHSα™ (Invitrogen Carlsbad, Calif.). Isolated colonies were screened by PCR using a sterile pipette tip stab as an inoculum into a reaction tube containing only water, followed by addition of the remaining PCR reaction cocktail (AccuPrime™ SuperMixII, Invitrogen Carlsbad, Calif.) and primers as described above.
Recombinant plasmids were isolated and purified using the QIAPrep® Spin Miniprep Kit (Qiagen) and characterized by restriction enzyme digestion (DraI, KpnI and HindIII from New England Biolabs, Beverly, Mass.). The plasmids were subsequently used to transform BW25113 (E. coli Genetics Stock Center, New Haven, Conn.) made competent using the calcium chloride method. Transformants were selected on Luria agar plates containing 34 μg/ml chloramphenicol. Plasmid DNA was isolated and purified using the QIAfilter™ Plasmid Midi Kit (Qiagen). DNA sequencing confirmed that the insert was mmat (SEQ ID NO: 34). The resulting plasmid incorporating a poly-histidine tag was designated pZA31 mmat.

Example 12

Method of Generating a Recombinant Host Cell Comprising an Exogenous Polynucleotide Encoding a Propionyl-CoA Carboxylase and an Exogenous Polynucleotide Encoding a Methylmalonyl-CoA Acyl Transferase (MMAT) Domain from Mycobacterium Mycocerosic Acid Synthase (MAS).

This example describes an exemplary method for making a cell comprising an exogenous polynucleotide comprising a nucleic acid sequence encoding a polypeptide that catalyzes the conversion of propionyl-CoA to methylmalonyl-CoA and an exogenous polynucleotide comprising a nucleic acid sequence encoding a polypeptide that catalyzes the conversion of methylmalonyl-CoA to methylmalonyl-ACP. The method entails co-transduction of E. coli with plasmids containing a propionyl-CoA carboxylase gene from Streptomyces coelicolor and a gene encoding a MMAT domain from Mycobacterium MAS.
E. coli BW25113 cells (E. coli Genetic Stock Center, New Haven, Conn.) were made chemically competent for plasmid DNA transformation by a calcium chloride method. Actively growing 50 ml E. coli cultures were grown to an optical density (at 600 nm) of ˜0.4. Cultures were quickly chilled on ice, and the bacteria were recovered by centrifugation at 2700×g for 10 minutes. The supernatant was discarded and pellets were gently suspended in 30 ml of an ice-cold 80 mM MgCl₂, 20 mM CaCl₂solution. Cells were again recovered by centrifugation at 2700×g for 10 minutes. The supernatant was discarded and pellets were gently resuspended in 2 ml of an ice-cold 0.1 M CaCl₂solution.
Cells were transformed on ice in pre-chilled 14 ml round-bottom centrifuge tubes. Approximately 25 ng of each of pTrcHisA mmat and pZA31-accA1-pccB (described above) was incubated on ice with 100 μl of competent cells for 30 minutes. The cells were heat shocked at 42° C. for 90 seconds and immediately placed on ice for two minutes. Pre-warmed SOC medium (500 μl; Invitrogen, Carlsbad, Calif.) was added and the cells allowed to recover at 37° C. with 225 rpm shaking. A portion (50 μl) of the transformed cell mix was spread onto selective LB agar 100 mg/ml ampicillin and 34 mg/ml chloramphenicol plates to select for cells carrying the pTrcHisA mmat and pZA31/32-accA1-pccB plasmids. Individual colonies were picked from each plate and streaked onto LB agar (with ampicillin and chloramphenicol) to confirm the antibiotic resistance phenotype. Restriction endonuclease digestion analysis of isolated plasmid DNA with HaeII verified the plasmid DNA pool for each strain. A sample of E. coli BW25113 comprising pTrcHisA mmat and pZA31-accA1-pccB was deposited with American Type Culture Collection (ATCC), 10801 University Blvd., Manassas, Va., on Dec. 14, 2010, under the provisions of the Budapest Treaty for the International Recognition of the Deposit of Microorganisms for the Purpose of Patent Procedure (“Budapest Treaty”), and assigned Deposit Accession No. [XXX] on [DATE].

Example 13

Construction of an Expression Vector Encoding Sorangium Cellulosum So ce 56 Methylmalonyl-CoA Epimerase

A S. cellulosum methylmalonyl-CoA epimerase synthetic gene (So ce epi) was designed and synthesized (SEQ ID NO: 37). The coding sequence was codon-optimization for expression in E. coli and modified to remove restriction sites (GenScript, Piscataway, N.J.). The nucleic acid sequence was flanked with a SacI site and a synthetic ribosome binding site from the pBAD vector (Invitrogen, Carlsbad, Calif.) adjacent to the translation initiation sequence (SEQ ID NO: 39). The synthetic gene was cloned as a SacI/PstI fragment into pTrcHisA Ec sbm and pTrcHisA Ec malE Ec sbm, with the resulting plasmids designated as pTrcHisA Ec sbm So ce epi and pTrcHisA Ec malE Ec sbm So ce epi, respectively.

Example 14

Construction of an Expression Vector Encoding Kribbella Flavida DSM 17836 Methylmalonyl-CoA Epimerase

A K. flavida methylmalonyl-CoA epimerase gene (Kf epi) was designed and synthesized (SEQ ID NO: 35). The coding sequence was optimized for expression in E. coli and restriction sites were removed (GenScript, Piscataway, N.J.). The gene was flanked with a Sad site and a synthetic ribosome binding site from the pBAD vector adjacent to the translation initiation sequence (SEQ ID NO: 39). The synthetic gene was cloned as a SacI/PstI fragment into pTrcHisA Ec sbm and pTrcHisA Ec malE Ec sbm. The resulting plasmids were designated pTrcHisA Ec sbm Kf epi and pTrcHisA Ec malE Ec sbm Kf epi, respectively.

Example 15

Production of Host Cells Producing Branched-Chain Fatty Acid

This example describes the production of branched-chain fatty acid using a recombinant host cell (e.g., E. coli) expressing polynucleotides encoding a propionyl-CoA carboxylase or a methylmalonyl-CoA mutase and a methylmalonyl-CoA epimerase, in some instances in conjunction with a polynucleotide encoding an acyl transferase and/or thioesterase.
It is useful to have the capacity to tailor the fatty acid chain length. Branched fatty acids of different lengths have different physical properties suitable for different commercial applications. To demonstrate the capacity to tailor the chain length of branched fatty acids, E. coli 'TesA (Cho, H., and J. E. Cronan, Jr. J. Biological Chemistry 270: 4216-9 (1995)) was incorporated into expression vectors described above and inserted into host cells. To create a pTrc Ec 'tesA expression vector, a truncated E. coli tesA ('tesA) cDNA (SEQ ID NO: 40) was created by PCR amplification of the E. coli tesA gene (GenBank Accession No. L06182). A 5′ primer (SEQ ID NO: 41) was designed to anneal after the 26th codon of tesA, modifying the 27th codon from an alanine to a methionine and creating a NcoI restriction site. A 3′ primer (SEQ ID NO: 43) incorporating a BamHI restriction site was designed. PCR was performed with 50 μl of Pfu Ultra II Hotstart 2× master mix (Agilent Technologies, Santa Clara, Calif.), 1 μl of a mix of the two primers (10 μmoles of each), 1 μl of E. coli BW25113 genomic DNA, and 48 μl of water. PCR began with a two minute incubation at 95° C., followed by 30 cycles of 20 seconds at 95° C. for denaturation, 20 seconds for annealing at 58° C., and 15 seconds at 72° C. for extension. The sample was incubated at 72° C. for three minutes and then held at 4° C. The PCR product (Ec 'tesA) was purified using a QIAquick® PCR Purification Kit (Qiagen, Valencia, Calif.). The bacterial expression vector pTrcHisA and the 'tesA PCR product were digested with NcoI and BamHI. The digested vector and insert were ligated using Fast-Link (Epicentre Biotechnologies, Madison, Wis.). The ligation mix was then used to transform E. coli TOP 10 cells (Invitrogen, Carlsbad, Calif.). Recombinant plasmids were isolated using a QIAPrep0 Spin Miniprep Kit (Qiagen) and characterized by gel electrophoresis of restriction digests with HaeII. DNA sequencing confirmed that the 'tesA insert had been cloned and that the insert encoded the expected amino acid sequence (SEQ ID NO: 45). The resulting plasmid was designated pTrc Ec 'tesA.
To limit gene expression, the truncated E. coli 'tesA gene was subcloned into the low-copy bacterial expression vector pZS21-MCS (Expressys, Ruelzheim, Germany). The expression vector pTrc Ec 'tesA was a template in a PCR reaction using a 5′ primer designed to create a flanking XhoI restriction site and include the pTrcHisA lac promoter (to replace the pZS21-MCS vector tet promoter) (SEQ ID NO: 46) and a 3′ primer incorporating a HindIII restriction site (SEQ ID NO: 47). PCR was performed with 50 μl of Pfu Ultra II Hotstart 2× master mix (Agilent Technologies, Santa Clara, Calif.), 1 μl of a mix of the two primers (10 μmoles of each), 1 μl of pTrc Ec 'tesA plasmid DNA (6 ng), and 48 μl of water. PCR began with a two minute incubation at 95° C., followed by 30 cycles of 20 seconds at 95° C. for denaturation, 20 seconds for annealing at 57° C., and 20 seconds at 72° C. for extension. The sample was incubated at 72° C. for three minutes and then held at 4° C. The PCR product was purified using a QIAquick® PCR Purification Kit (Qiagen, Valencia, Calif.). The bacterial expression vector pZS21-MCS and the Ec 'tesA PCR product were digested with XhoI and HindIII. The digested vector and insert were ligated using Fast-Link (Epicentre Biotechnologies, Madison, Wis.). The ligation mix was then used to transform E. coli TOP10 cells (Invitrogen, Carlsbad, Calif.). Recombinant plasmids were isolated using a QIAPrep® Spin Miniprep Kit (Qiagen) and characterized by gel electrophoresis of restriction digests with HaeII. DNA sequencing confirmed that the 'tesA insert had been cloned and that the insert encoded the expected amino acid sequence (SEQ ID NO: 45). The resulting plasmid was designated pZS22 Ec 'tesA.
An E. coli strain deficient in fatty acid degradation (Voelker, T. A., and H. M. Davies. J. Bacteriology 176: 7320-7 (1994)) and able to regulate transcription of recombinant genes was generated as follows. An E. coli K-12 strain (K27) defective in fadD lacks the fatty acyl-CoA synthetase responsible for an initial step in fatty acid degradation. The strain K27 (F—, tyrT58(AS), fadD88, mel-1; CGSC Strain #5478) was obtained from the E. coli Genetic Stock Center (New Haven, Conn.). A genomic regulation cassette from strain DH5αZ1 [lacl^q, PN25-tetR, Sp^R, deoR, supE44, Δ(lacZYA-argFV169), φ80 lacZΔM15 (Expressys, Ruelzheim, Germany)] was introduced into the host strain. The transducing phage P1vir was charged with DH5αZ1 DNA as follows. A logarithmically growing culture (5 ml LB broth containing 0.2% glucose and 5 mM CaCl₂) of donor strain, DH5αZ1, was infected with a 100 μl of a lysate stock of P1vir phage. The culture was further incubated three hours for the infected cells to lyse. The debris was pelleted, and the supernatant was further cleared through a 0.45 μm syringe filter unit. The fresh lysate was titered by spotting 10 μl of serial 1:10 dilutions of lysate in TM buffer (10 mM MgSO₄/10 mM Tris.Cl, pH 7.4) onto a 100 mm LB (with 2.5 mM CaCl₂) plate overlayed with a cultured lawn of E. coli in LB top agar (with 2.5 mM CaCl₂). The process was repeated using the newly created phage stock until the phage titer surpassed 10⁹pfu/ml.
The higher titer phage stock was used to transduce fragments of the DH5αZ1 genome into a recipient K27 strain. An overnight culture (1.5 ml) of K27 was pelleted and resuspended in 750 μl of a P1 salts solution (10 mM CaCl₂/5 mM MgSO₄). 100 μl of the suspended cells was inoculated with varying amounts of DH5αZ1 donor P1vir lysate (1, 10, and 100 μl) in sterile test tubes. The phage was allowed to adsorb to the cells for 30 minutes at 37° C. Absorption was terminated by addition of 1 ml LB broth plus 200 μl of 1 M sodium citrate, and the cultures were further incubated for 1 hour at 37° C. with aeration. The cultures were pelleted, and the cells suspended in 100 μl of LB broth (plus 0.2 M sodium citrate) and spread onto LB agar plates with 50 μg/mL spectinomycin. Spectinomycin-resistant strains were isolated, and genomic DNAs were screened by PCR for the presence of tetR, lacI^qand fadD88. One such transductant was named K27-Z1 and used in further studies.
To transform K27-Z1, competent cells were placed on ice in pre-chilled 14 ml round bottom centrifuge tubes. Each plasmid was incubated with 50 μl of chemically competent K27-Z1 cells (Cohen, S. N., Change, A. C. Y., and L. Hsu. Proceedings National Academy Sciences U.S.A. 69: 2110-4 (1972)) for 30 minutes. The cells were heat shocked at 42° C. for 90 seconds and immediately placed on ice for two minutes. Pre-warmed SOC medium (250 μl) (Invitrogen, Carlsbad, Calif.) was added, and the cells were allowed to recover at 37° C. with 125 rpm shaking for one hour. Transformed cell mix (20 μl) was spread onto selective LB agar with 100 μg/ml ampicillin to select for cells carrying the pTrcHisA-based plasmids. Transformed cell mix (50 μl) was spread onto LB agar with 34 μg/ml chloramphenicol to select for cells carrying the pZA31-based plasmids. Transformed cell mix (150 μl) was spread onto LB agar with 100 μg/ml ampicillin and 34 μg/ml chloramphenicol to select for cells carrying both the pTrcHisA-based and pZA31-based plasmids. In some cases, the creation of triple transformants required two transformations: a double transformant was originally created, made competent, and transformed by a third plasmid.
Using the methods described above, E. coli strain K27-Z1 was transduced with pTrcHisA pZA31 (control), pZA31 mutAB Ss epi, pTrcHisA Ec sbm, and pTrcHisA Ec sbm/pZA31 Mb mmat. The bacteria were cultured in M9 with glycerol (0.2%) at 22° C. in flasks that were coated with black Scotch duct tape. After the bacteria reached an optical density (600 nm) of 0.4, a mix of IPTG, anhydrotetracycline, arabinose and hydroxocobalamin hydrochloride was added to the culture, giving final concentrations of 1 mM, 100 ng/ml, 0.2%, and 20 μM, respectively. Twenty-four hours later, the bacteria were harvested for coenzyme A analysis. Methylmalonyl-CoA production is illustrated in FIG. 24. Host cells producing exogenous methylmalonyl-CoA mutase and methylmalonyl-CoA epimerase (encoded by pZA31 mutAB Ss epi) produced over 25 ng methylmalonyl-CoA per ml culture. Host cells comprising additional copies of the Sbm (methylmalonyl-CoA mutase) coding sequence produced over three times the amount of methylmalonyl-CoA per ml of culture, and co-expression of an methylmalonyl-CoA acyl transferase reduced the amount of methylmalonyl-CoA present in the culture medium.
Production of methylmalonyl-CoA in host cells expressing exogenous propionyl-CoA carboxylase also was studied and is illustrated in FIG. 25. BW25113 (control) and BW25113 containing pZA31-accA1-pccB (labeled as Pcc in the figure) were cultured in LB, and the coenzyme-A thioesters were isolated and characterized as described above. Host cells comprising a polynucleotide encoding an exogenous propionyl-CoA carboxylase produced over about 15 ng methylmalonyl-CoA per ml of culture.
When Ec 'tesA was present, less longer-chain (fifteen and seventeen carbons) and more mid-chain (thirteen carbons) branched fatty acids were produced by the host cell, indicating that production of thioesterase increases the proportion of medium chain-length branched fatty acids produced by the inventive method.

Example 16

Analysis of Scattered Branched Fatty Acid by Two-Dimensional (2D) Gas Chromatography

To identify branched fatty acids produced by recombinant E. coli produced as described herein, fatty acids were isolated from bacterial cultures and derivatives were generated to facilitate identification. The fatty acid derivatives were separated by 2D gas chromatography and mass spectrometry was used to characterize fragmented samples. Derivatization of fatty acids to their 4,4′ dimethyloxazoline derivatives prior to analysis via mass spectrometry has been described (Zhang, J. Y., QT. Yu, B. N. Liu and Z. H. Huang, Biomed Env. Mass Spectrom. 15:33 (1988)). By careful examination of minor spectral differences, it possible to determine the location of branch points on the backbones of fatty acid derivatives.
One liter of bacterial samples in LB (modified to contain only 0.5 mg/ml sodium chloride, unless otherwise indicated) with cyanocobalamin (20 μM) were cultured at 22° C. for 25 hours following induction with IPTG, anhydrotetracycline, and arabinose. A cell pellet was collected by centrifugation at 3500 rpm, and the supernatant was discarded. The cell pellet was suspended in the remaining liquid, and the slurry was transferred into Pyrex tubes (#9826, Corning Inc., Lowell, Mass.). An equal volume of chloroform was added, and the sample was dried at room temperature overnight.
To produce samples for analysis, cell pellets (0.5 grams) were placed in a round bottom flask, and 0.5 grams of KOH pellets and 25 ml of water were added. The E. coli pellets and KOH solution were refluxed for three hours, and the sample was allowed to cool. Concentrated HCl was added drop-wise, using a methyl orange endpoint to ensure fatty carboxylic acids were in the acid form. The acidified aqueous solution was then extracted three times with 25 ml aliquots of hexane to extract the fatty acids into the organic layer.
To convert fatty acid to oxazoline derivatives, the hexane extract was evaporated to dryness and reconstituted into 5 ml of hexane to which sodium sulfate was added as a drying agent. After evaporating the sample to a 1 ml volume, a portion (0.6 ml) was decanted into a Reactitherm™ vial. The hexane in the Reactitherm™ vial was again evaporated to dryness, and 2 ml of 2-methyl-2-aminopropanol was added. The vial was capped and heated for 4 hours at 200° C. The cooled 2-methyl-2-aminopropanol solution was transferred to a scintillation vial, to which 5 ml of methylene chloride was added. The sample was washed with three 5 ml volumes of water. Sodium sulfate was added to the methylene chloride to remove any residual water, and an aliquot was transferred to a GC vial for analysis.
The derivatized samples were analyzed on a Leco Pegasus 4D Comprehensive 2D gas chromatograph time-of-flight mass spectrometer equipped with a 30M Supelco GammaDex 120 (Supelco 24307) column in the first dimension and a 2M Varian VF5-MS (Varian CP9034) column in the second dimension. Retention times of key chain-length fatty acids (in both first and second dimensions) in test samples were confirmed by identical preparation and analysis of a Supleco (47080-U) BAME (bacterial acid methyl ester) standard mixture. Using these columns, 4,4′ dimethyloxazoline-derivatized branched-chain fatty acids were expected to elute prior to their linear chain-length homologs in the first dimension, and this was confirmed by the iso and anteiso structural isomers of C15 methyl esters (derivatized to their 4,4′-dimethyloxazoline derivatives) in the BAME standard reference above.
The profile of fatty acids produced by two strains was compared. The first strain was engineered to produce branched fatty acids [BL21 Star (DE3) (pTrcHisA Ec sbm So ce epi pZA31 mmat)] and the second was a control strain [BL21 Star (DE3) (pTrcHisA pZA31)]. A sample of E. coli BL21 Star (DE3) comprising pTrcHisA Ec sbm So ce epi and pZA31 mmat was deposited with American Type Culture Collection (ATCC), 10801 University Blvd., Manassas, Va., on Dec. 14, 2010, under the provisions of the Budapest Treaty for the International Recognition of the Deposit of Microorganisms for the Purpose of Patent Procedure (“Budapest Treaty”), and assigned Deposit Accession No. [XXX] on [DATE]. The sample from the first strain revealed several peaks in the region where branched fatty acids were expected (FIG. 26), whereas the sample from the control strain revealed no such peaks (FIG. 27). For example, several peaks (labeled 54, 55, and 57) were in a position consistent with branched C15 acids, and peaks 137 and 139 were in a position expected for branched C17 acids. Mass spectrometry established that these peaks comprise branched fatty acids.
The mass spectral fragmentation pattern of oxazoline derivatives was used to confirm that the fatty acids identified using 2D GC contained branches. Oxazoline derivatives fragment along the length of the carbon chain starting from the functional end of the molecule. If a branch point occurs along the backbone, there is a gap in the mass spectrum pattern; which peak is missing (or reduced) depends on the location of the branch. FIG. 28 depicts the mass spectra of the peaks labeled 54, 55, and 57 in FIG. 26 as oxazoline derivatives of methyl-branched tetradecanoic fatty acids. The ions circled exhibit reduced or no intensity relative to the reference spectrum of linear pentadecanoic fatty acid (bottom spectrum), and were assigned as 8-methyl, 10-methyl, and 12-methyl (anteiso) tetradecanoic fatty acid (all as oxazoline derivatives). Peak 57 was tentatively identified as the anteiso C15 oxazoline derivative despite the similarity to the mass spec data for the linear sample because 1) peak 61 migrated at the position of an anteiso C15 standard on 2D gas chromatography, 2) the 252 molecular weight ion is present in slightly lower amounts relative to the nearby 238 and 266 molecular weight ions, and 3) anteiso compounds can be difficult to identify by this technique. The 8- and 10-branched fatty acids are shown in the top two profiles of FIG. 28, readily identified by the almost complete absence of the fragment circled. Peaks 137 and 139 in FIG. 26 were assigned as 8-methylhexadecanoic acid and 12-methylhexadecanoic acids (as oxazoline derivatives). Thus, B132 Star (DE3) (pTrcHisA Ec sbm So ce epi pZA31 mmat) (i.e., a recombinant microbe comprising overexpressed or recombinant polynucleotides encoding a methylmalonyl-CoA mutase, a methylmalonyl-CoA epimerase, and an acyl transferase) generated branched-chain C15 and C17 fatty acids comprising methyl branches on even-number carbons.
Branched fatty acid production also was observed in host cells producing exogenous propionyl-CoA carboxylase and Streptomyces coelicolor methylmalonyl-CoA mutase. The propionyl-CoA carboxylase gene-containing strain produced the branched fatty acids shown in Table F.

TABLE F

	Molecular Weight

				as fatty
Peak #	Proposed Compound ID	Formula	DMOX	acid

38	6-methyl, dodecanoic acid	C₁₃H₃₃	267	214
	(DMOX)	(C₄H₈NO)
40	8-methyl, dodecanoic acid	C₁₃H₃₃	267	214
	(DMOX)	(C₄H₈NO)
61	6-methyl, tridecanoic acid	C₁₄H₃₅	281	228
	(DMOX)	(C₄H₈NO)
62	8-methyl, tridecanoic acid	C₁₄H₃₅	281	228
	(DMOX)	(C₄H₈NO)
101	6-methyl, tetradecanoic acid	C₁₅H₃₇	295	242
	(DMOX)	(C₄H₈NO)
103	10-methyl, tetradecanoic acid	C₁₅H₃₇	295	242
	(DMOX)	(C₄H₈NO)
140	10-methyl, pentadecanoic acid	C₁₆H₃₉	309	256
	(DMOX)	(C₄H₈NO)
182	8-methyl, hexadecanoic acid	C₁₇H₄₁	323	270
	(DMOX)	(C₄H₈NO)
189	12-methyl, hexadecanoic acid	C₁₇H₄₁	323	270
	(DMOX)	(C₄H₈NO)

The S. coelicolor methylmalonyl-CoA mutase gene-containing microbe (BL21 Star (DE3) harboring pZA31 mutAB Ss epi pTrcHisA mmat) produced four branched fatty acids: 6-methyltetradecanoic acid, 10-methyltetradecanoic acid, 6-methylhexadecanoic acid, and 12-methylhexadecanoic acid.
Using 2D gas chromatography and mass spectrometry, fatty acid profiles were compared for two recombinant strains comprising Ec sbm, So ce epi, Mb mmat and containing or lacking a thioesterase coding sequence ('tesA). The amount of branched C15 fatty acids relative to branched C17 fatty acids was greater in the 'tesA-containing strain. The area percent ratio of branched C15 fatty acid to branched C17 fatty acids in K27-Z1 (pTrcHisA Ec sbm So ce epi pZA31 mmat) was 1.4, while the ratio produced by K27-Z1 (pTrcHisA Ec sbm So ce epi pZA31 mmat pZS22 Ec 'tesA) was 7.0. Expression of a thioesterase shortened the chain length of branched fatty acids.
These results demonstrate that a cell of the invention producing propionyl-CoA carboxylase or producing methylmalonyl-CoA mutase, methylmalonyl-CoA epimerase, and acyl transferase generates branched-chain fatty acids comprising methyl branches on even-number carbons. Recombinant host cells further comprising a polynucleotide encoding a thioesterase preferentially produce fatty acid comprising shorter chain length.
The dimensions and values disclosed herein are not to be understood as being strictly limited to the exact numerical values recited. Instead, unless otherwise specified, each such dimension is intended to mean both the recited value and a functionally equivalent range surrounding that value. For example, a dimension disclosed as “40 mm” is intended to mean “about 40 mm.”
Every document cited herein, including any cross referenced or related patent or application, is hereby incorporated herein by reference in its entirety unless expressly excluded or otherwise limited. The citation of any document is not an admission that it is prior art with respect to any invention disclosed or claimed herein or that it alone, or in any combination with any other reference or references, teaches, suggests or discloses any such invention. Further, to the extent that any meaning or definition of a term in this document conflicts with any meaning or definition of the same term in a document incorporated by reference, the meaning or definition assigned to that term in this document shall govern.
While particular embodiments of the invention have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of this invention.

Claims

1. A method for producing branched-chain fatty acid comprising a methyl on one or more even number carbons, the method comprising culturing a cell comprising

(aa) an exogenous or overexpressed polynucleotide comprising a nucleic acid sequence encoding a polypeptide that catalyzes the conversion of propionyl-CoA to methylmalonyl-CoA and/or (bb) an exogenous or overexpressed polynucleotide comprising a nucleic acid sequence encoding a polypeptide that catalyzes the conversion of succinyl-CoA to methylmalonyl-CoA,

under conditions allowing expression of the polynucleotide(s) and production of branched-chain fatty acid, wherein the cell produces more branched-chain fatty acid comprising a methyl on one or more even number carbons than an otherwise similar cell that does not comprise the polynucleotide(s).

2. The method of claim 1 further comprising extracting from culture the branched-chain fatty acid or a product of the branched-chain fatty acid.

3. The method of claim 2, wherein the polypeptide that catalyzes the conversion of propionyl-CoA to methylmalonyl-CoA is a propionyl-CoA carboxylase and/or the polypeptide that catalyzes the conversion of succinyl-CoA to methylmalonyl-CoA is a methylmalonyl-CoA mutase.

4. The method of claim 3, wherein (i) the propionyl-CoA carboxylase is Streptomyces coelicolor PccB and AccA1 or PccB and AccA2 and/or (ii) the methylmalonyl-CoA mutase is Janibacter sp. HTCC2649 methylmalonyl-CoA mutase, S. cinnamonensis MutA and MutB, or E. coli Sbm.

5. The method of claim 3, wherein (i) the methylmalonyl-CoA mutase comprises an amino acid sequence having at least about 80% sequence identity to the amino acid sequence set forth in SEQ ID NOs: 3, 4, or 28 and/or (ii) the propionyl-CoA carboxylase comprises an amino acid sequence having at least about 80% sequence identity to the amino acid sequence set forth in SEQ ID NOs: 9 and 10.

6. The method of claim 3, wherein the cell comprises an exogenous or overexpressed polynucleotide comprising a nucleic acid sequence encoding a methylmalonyl-CoA mutase and further comprises an exogenous or overexpressed polynucleotide comprising a nucleic acid sequence encoding a methylmalonyl-CoA epimerase.

7. The method of claim 2, wherein the cell further comprises an exogenous or overexpressed polynucleotide encoding an acyl transferase lacking polyketide synthesis activity and/or an exogenous or overexpressed polynucleotide comprising a nucleic acid sequence encoding a thioesterase.

8. The method of claim 7, wherein the acyl transferase is FabD, an acyl transferase domain of a polyketide synthase, or an acyl transferase domain of Mycobacterium mycocerosic acid synthase.

9. The method of claim 2, wherein the cell has been modified to attenuate endogenous methylmalonyl-CoA mutase activity, endogenous methylmalonyl-CoA decarboxylase activity, and/or endogenous acyl transferase activity.

10. The method of claim 2, wherein the cell produces a Type II fatty acid synthase.

11. The method of claim 10, wherein the cell is Escherichia coli.

12. A branched-chain fatty acid produced by the method of claim 1.

13. A cell comprising:

(i) an exogenous or overexpressed polynucleotide comprising a nucleic acid sequence encoding an acyl transferase lacking polyketide synthesis activity, and

(ii) an exogenous or overexpressed polynucleotide comprising a nucleic acid sequence encoding a propionyl-CoA carboxylase and/or an exogenous or overexpressed polynucleotide comprising a nucleic acid sequence encoding a methylmalonyl-CoA mutase,

wherein the polynucleotide(s) are expressed and the cell produces more branched-chain fatty acid comprising a methyl on one or more even number carbons than an otherwise similar cell that does not comprise the polynucleotide(s).

14. The cell of claim 13, wherein (i) the propionyl-CoA carboxylase is Streptomyces coelicolor PccB and AccA1 or PccB and AccA2 and/or (ii) the methylmalonyl-CoA mutase is Janibacter sp. HTCC2649 methylmalonyl-CoA mutase, S. cinnamonensis MutA and MutB, or E. coli Sbm.

15. The cell of claim 13, wherein (i) the methylmalonyl-CoA mutase comprises an amino acid sequence having at least about 80% sequence identity to the amino acid sequence set forth in SEQ ID NOs: 3, 4, or 28 and/or (ii) the propionyl-CoA carboxylase comprises an amino acid sequence having at least about 80% sequence identity to the amino acid sequence set forth in SEQ ID NOs: 9 and 10.

16. The cell of claim 13, wherein the cell comprises an exogenous or overexpressed polynucleotide comprising a nucleic acid sequence encoding a methylmalonyl-CoA mutase and further comprises an exogenous or overexpressed polynucleotide comprising a nucleic acid sequence encoding a methylmalonyl-CoA epimerase.

17. The cell of claim 13, wherein the acyl transferase is FabD, an acyl transferase domain of a polyketide synthase, or an acyl transferase domain of Mycobacterium mycocerosic acid synthase.

18. The cell of claim 13, wherein the cell further comprises an exogenous or overexpressed polynucleotide comprises a nucleic acid sequence encoding a thioesterase.

19. The cell of claim 13, wherein the cell has been modified to attenuate endogenous methylmalonyl-CoA mutase activity, endogenous methylmalonyl-CoA decarboxylase activity, and/or endogenous acyl transferase activity.

20. The cell of claim 13, wherein the cell is Escherichia coli.