Publications

• Microbial production of R-3-hydroxybutyric acid by recombinant E. coli harboring genes of phbA, phbB, and tesB.

  Liu Q., Ouyang S.P., Chung A., Wu Q., Chen G.Q.

  Production of R-3-hydroxybutyric acid (3HB) was observed when genes of beta-ketothiolase (PhbA), acetoacetyl CoA reductase (PhbB), and thioesterase II (TesB) were jointly expressed in Escherichia coli. TesB, generally regarded as a medium chain length acyl CoA thioesterase, was found, for the firs ... >> More

  Production of R-3-hydroxybutyric acid (3HB) was observed when genes of beta-ketothiolase (PhbA), acetoacetyl CoA reductase (PhbB), and thioesterase II (TesB) were jointly expressed in Escherichia coli. TesB, generally regarded as a medium chain length acyl CoA thioesterase, was found, for the first time, to play an important role for transforming short chain length 3-hydroxybutyrate-CoA to its free fatty acid, namely, 3HB. E. coli BW25113 (pSPB01) harboring phbA, phbB, and tesB genes produced approximately 4 g/l 3HB in shake flask culture within 24 h with glucose used as a carbon source. Under anaerobic growth conditions, 3HB production was found to be more effective, achieving 0.47 g 3HB/g glucose compared with only 0.32 g 3HB/g glucose obtained from aerobic process. When growth was conducted on sodium gluconate, 6 g/l 3HB was obtained. In a 24-h fed-batch growth process conducted in a 6-l fermentor containing 3 l glucose mineral medium, 12 g/l 3HB was produced from 17 g/l cell dry weight (CDW). This was the highest 3HB productivity achieved by a one-stage fermentation process for 3HB production. << Less

  Appl. Microbiol. Biotechnol. 76:811-818(2007) [PubMed] [EuropePMC]

• Metabolic engineering of Escherichia coli for enhanced production of (R)- and (S)-3-hydroxybutyrate.

  Tseng H.C., Martin C.H., Nielsen D.R., Prather K.L.

  Synthetic metabolic pathways have been constructed for the production of enantiopure (R)- and (S)-3-hydroxybutyrate (3HB) from glucose in recombinant Escherichia coli strains. To promote maximal activity, we profiled three thiolase homologs (BktB, Thl, and PhaA) and two coenzyme A (CoA) removal me ... >> More

  Synthetic metabolic pathways have been constructed for the production of enantiopure (R)- and (S)-3-hydroxybutyrate (3HB) from glucose in recombinant Escherichia coli strains. To promote maximal activity, we profiled three thiolase homologs (BktB, Thl, and PhaA) and two coenzyme A (CoA) removal mechanisms (Ptb-Buk and TesB). Two enantioselective 3HB-CoA dehydrogenases, PhaB, producing the (R)-enantiomer, and Hbd, producing the (S)-enantiomer, were utilized to control the 3HB chirality across two E. coli backgrounds, BL21Star(DE3) and MG1655(DE3), representing E. coli B- and K-12-derived strains, respectively. MG1655(DE3) was found to be superior for the production of each 3HB stereoisomer, although the recombinant enzymes exhibited lower in vitro specific activities than BL21Star(DE3). Hbd in vitro activity was significantly higher than PhaB activity in both strains. The engineered strains achieved titers of enantiopure (R)-3HB and (S)-3HB as high as 2.92 g liter(-1) and 2.08 g liter(-1), respectively, in shake flask cultures within 2 days. The NADPH/NADP+ ratio was found to be two-to three-fold higher than the NADH/NAD+ ratio under the culture conditions examined, presumably affecting in vivo activities of PhaB and Hbd and resulting in greater production of (R)-3HB than (S)-3HB. To the best of our knowledge, this study reports the highest (S)-3HB titer achieved in shake flask E. coli cultures to date. << Less

  Appl. Environ. Microbiol. 75:3137-3145(2009) [PubMed] [EuropePMC]

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