Enhanced Production of (R)-l,2-Propanediol by Metabolically Engineered Escherichia coli

1,2-Propanediol (1,2-PD) is a major commodity chemical currently derived from propylene. Previously, we have demonstrated the production of enantiomerically pure (.R)-l,2-propanediol from glucose by an engineered E. coli expressing genes for NADHlinked glycerol dehydrogenase and methyiglyoxal synthase. In this work, we investigate three methods to improve 1,2-PD in E. coli. First, we investigated improving the host by eliminating production of a byproduct, lactate. To do this, we constructed strains with mutations in two enzymes involved in lactate production, lactate dehydrogenase and glyoxalase 1. (Surprisingly, when mutations were made in its ability to produce lactate, one strain of E. coli [MM294], produced a small amount of 1,2-PD without any added genes.) Second, we constructed a complete pathway to 1,2-PD from the glycolytic intermediate, dihydroxyacetone phosphate. Our previous 1,2-PD producing strains relied on at least one endogenous E. coli activity and only produced 0.7 g/L of 1,2-PD. The complete pathway involved the coexpression of methyiglyoxal synthase (.mgs), glycerol dehydrogenase (gldA), and either yeast alcohol dehydrogenase (adhl) orE. coli 1,2-propanediol oxidoreductase (fucO). Third, we investigated bioprocessing improvements by carrying out a fed-batch fermentation with the best engineered strain (expressing mgs, gldA, and fucO). A final titer of 4.5 g/L of (R)- 1,2-PD was produced, with a final yield of 0.19 g of 1,2-PD per gram of glucose consumed. This work provides a basis for further strain and process improvement.