Fermentative production of enantiomerically pure S-1,2-propanediol from glucose by engineered E. coli strain

Abstract

The pure stereoisomers of 1,2-propanediol (1,2-PDO) could be used as starting materials to synthesize high value-added specialty chemicals and chiral pharmaceutical products. As the stereoisomers of 1,2-PDO cannot be obtained by traditional chemical synthesis processes, biotechnological processes have gained increasing attention. However, to our knowledge, the production of S-1,2-PDO directly from glucose has not been previously reported. In this study, we demonstrate a novel artificial pathway to convert l-lactic acid to S-1,2-PDO and its integration into the genome of Escherichia coli strain BW25113∆poxB with synchronous deletion of genes responsible for branch metabolic pathways from glucose. l-lactate production was increased by replacing the native d-lactate dehydrogenase with the l-lactate dehydrogenase from Bacillus coagulans. The methylglyoxal bypass pathway was blocked to avoid synthesis of a racemic mixture of d- and l-lactate and prevent the accumulation of methylglyoxal, a toxic intermediate. To further improve the yield of S-1,2-PDO, a novel cofactor regeneration system was introduced by combining pyruvate decarboxylase and acetaldehyde-CoA dehydrogenase II to simultaneously regenerate NADH and the CoA donor of acetyl-CoA for the lactate conversion pathway. Finally, 13.7 mM S-1,2-PDO with >99 % enantiomeric purity was directly produced from glucose by disrupting the major carbon-competing pathways and strengthening the lactate transformation pathway. This study demonstrates the first attempt to synthesize S-1,2-PDO by direct fermentation of glucose.