Biosynthesis of 2‐Hydroxyacid‐Containing Polyhydroxyalkanoates by Employing butyryl‐CoA Transferases in Metabolically Engineered Escherichia coli. Issue 11 (21st September 2017) - David, Yokimiko
Abstract : The authors previously reported the production of polyhydroxyalkanoates (PHAs) containing 2‐hydroxyacid monomers by expressing evolved Pseudomonas sp. 6‐19 PHA synthase and Clostridium propionicum propionyl‐CoA transferase in engineered microorganisms. Here, the authors examined four butyryl‐CoA transferases from Roseburia sp., Eubacterium hallii, Faecalibacterium prausnitzii, and Anaerostipes caccae as potential CoA‐transferases to support synthesis of polymers having 2HA monomer. In vitro activity analyses of the four butyryl‐CoA transferases suggested that each butyryl‐CoA transferase has different activities towards 2‐hydroxybutyrate (2HB), 3‐hydroxybutyrate (3HB), and lactate (LA). When Escherichia coli XL1‐Blue expressing Pseudomonas sp. 6‐19 PhaC1437 along with one butyryl‐CoA transferase is cultured in chemically defined MR medium containing 20 g L −1 of glucose, 2 g L −1 of sodium 3‐hydroxybutyrate, and various concentrations of sodium 2‐hydroxybutyrate, PHAs consisting of 3HB, 2HB, and LA are produced. The monomer composition of PHAs agreed well with the substrate specificities of butyryl‐CoA transferases from E. hallii, F. prausnitzii, and A. caccae, but not Roseburia sp. When E. coli XL1‐Blue expressing PhaC1437 and E. hallii butyryl‐CoA transferase is cultured in MR medium containing 20 g L −1 of glucose and 2 g L −1 of sodium 2‐hydroxybutyrate, P(65.7 mol% 2HB‐ co ‐34.3 mol% LA) is produced with the highest PHA content of 30 wt%. Butyryl‐CoA transferases also supported the production of P(3HB ‐co‐ 2HB ‐co‐ LA) from glucose as the sole carbon source in E. coli XL1‐Blue strains when one of these bct genes is expressed with phaC1437, cimA3.7, leuBCD, panE, and phaAB genes. Butyryl‐CoA transferases characterized in this study can be used for engineering of microorganisms that produce PHAs containing novel 2‐hydroxyacid monomers. Abstract : Polyhydroxyalkanoates (PHAs) are biodegradable polymers that can be utilized in various fields. In this study, four butyryl‐CoA transferases for the synthesis of 2‐hydroxyacid containing PHAs in recombinant Escherichia coli strains is examined. Butyryl‐CoA transferases examined in this study can be used for the synthesis of 2‐hydroxyacid containing PHAs without much reduced cell growth rate of the host strain.