[High-efficiency L-lactate production from glycerol by metabolically engineered Escherichia coli]

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%.