Efficient synthesis of D-phenyllactic acid by a whole-cell biocatalyst co-expressing glucose dehydrogenase and a novel D-lactate dehydrogenase from Lactobacillus rossiae

D-Phenyllactic acid is a versatile natural organic acid, which is used as an antiseptic agent, monomer of the biodegradable material poly-phenyllactic acid and in the synthesis chiral intermediate of pharmaceuticals. In this report, the novel NADH-dependent D-lactate dehydrogenase LrLDH was identified by screening a shotgun genome of Lactobacillus rossiae. To improve cofactor regeneration, the Exiguobacterium sibiricum glucose dehydrogenase EsGDH was overexpressed together with LrLDH in E. coli BL21(DE3)-pCDFDuet-1-gdh-ldh. The total enzyme activity in the fermentation broth of E. coli BL 21(DE3)- pCDFDuet-1-gdh-ldh peaked at 2359.0 U l(-1) when induced by 10 g l(-1) lactose at 28 degrees C and 150 rpm for 14 h. The biocatalytic reduction of sodium phenylpyruvate to D-Phenyllactic acid was successfully carried out using whole cells of the engineered E. coli. Under the optimized biocatalysis conditions, 50 g l(-1) sodium phenylpyruvate was completely converted to D-Phenyllactic acid with a space-time yield and enantiomeric excess of 262.8 g l(-1) day(-1) and > 99.5%, respectively. To our best knowledge, it is the highest productivity reported to date, with great potential for the mass production of D-Phenyllactic acid.