High-efficiency L-lactate production from glycerol by metabolically engineered Escherichia coli / 生物工程学报

High-efficient conversion of glycerol to L-lactate is beneficial for the development of both oil hydrolysis industry and biodegradable materials manufacturing industry. In order to construct an L-lactate producer, we first cloned a coding region of gene BcoaLDH encoding an L-lactate dehydrogenase from Bacillus coagulans CICIM B1821 and the promoter sequence (P(ldhA)) of the D-lactate dehydrogenase (LdhA) from Escherichia coli CICIM B0013. Then we assembled these two DNA fragments in vitro and yielded an expression cassette, P(ldhA)-BcoaLDH. Then, the cassette was chromosomally integrated into an ldhA mutant strain, Escherichia coli CICIM B0013-080C, by replacing lldD encoding an FMN-dependent L-lactate dehydrogenase. An L-lactate higher-producer strain, designated as E. coli B0013-090B, possessing genotype of lldD::P(ldhA)-BcoaLDH, deltaack-pta deltapps deltapflB deltadld deltapoxB deltaadhE deltafrdA and deltaldhA, was generated. Under the optimal condition, 132.4 g/L L-lactate was accumulated by B0013-090B with the lactate productivity of 4.90 g/Lh and the yield of 93.7% in 27 h from glycerol. The optical purity of L-lactate in broth is above 99.95%.

Temperature-switched high-efficiency D-lactate production from glycerol / 生物工程学报

Glycerol from oil hydrolysis industry is being considered as one of the abundent raw materials for fermentation industry. In present study, the aerobic and anaerobic metabolism and growth properties on glycerol by Esherichia coli CICIM B0013-070, a D-lactate over-producing strain constructed previously, at different temperatures were investigated, followed by a novel fermentation process, named temperature-switched process, was established for D-lactate production from glycerol. Under the optimal condition, lactate yield was increased from 64.0% to 82.6%. Subsequently, the yield of D-lactate from glycerol was reached up to 88.9% while a thermo-inducible promoter was used to regulate D-lactate dehydrogenase transcription.

Elimination of succinate and acetate synthesis in recombinant Escherichia coli for D-lactate production / 生物工程学报

When Escherichia coli CICIM B0013-030 (B0013, ack-pta, pps, pflB) was used for D-lactate production, succinate and acetate were the main byproducts (as much as 11.9 and 7.1% the amount of lactate respectively). In order to decrease the byproduct levels, we inactivated succinate and acetate synthesis in B0013-030. Two recombinant plasmids containing mutation cassettes of frdA::difGm and tdcDE::difGm respectively were constructed first. The mutation cassettes were used to delete the target genes on the chromosomal by Red recombination. Subsequently, the antibiotic resistance gene was excised from the chromosomal by Xer recombination. Thereby, mutants B0013-040B (B0013-030, frdA) and B0013-050B (B0013-040B, tdcDE) were produced. D-lactate producing abilities of the engineered strains were tested both in shake flasks and in bioreactors using two-phase fermentation (aerobic growth and anaerobic fermentation) with glucose as the sole carbon source. When fermentation was carried out in shake flasks, inactivation of frdA in B0013-030 to produce B0013-040B reduced succinate accumulation by 80.8%. When tested in a 7-liter bioreactor, B0013-040B accumulated 114.5 g/L D-lactate of over 99.9% optical purity. However, 1.0 g/L succinate and 5.4 g/L acetate still remained in the broth. Further inactivation of tdcD and tdcE genes in B0013-040B to produce B0013-050B decreased acetate and succinate accumulation to 0.4 g/L and 0.4 g/L respectively, and lactate titer was as much as 111.9 g/L (tested in the 7-liter bioreactor). In lightof the lower byproduct levels and high lactate production, strain B00 13-050B may prove useful for D-lactate production.