Metabolic engineering of a 1,2-propanediol pathway in Escherichia coli

Abstract

1,2-Propanediol (1,2-PD) is a major commodity chemical that is currently derived from propylene, a nonrenewable resource. A goal of our research is to develop fermentation routes to 1,2-PD from renewable resources. Here we report the production of enantiomerically pure R-1,2-PD from glucose in Escherichia coli expressing NADH-linked glycerol dehydrogenase genes (E. coli gldA or Klebsiella pneumoniae dhaD). We also show that E. coli overexpressing the E. coli methylglyoxal synthase gene (mgs) produced 1,2-PD. The expression of either glycerol dehydrogenase or methylglyoxal synthase resulted in the anaerobic production of approximately 0.25 g of 1,2-PD per liter. R-1,2-PD production was further improved to 0.7 g of 1,2-PD per liter when methylglyoxal synthase and glycerol dehydrogenase (gldA) were coexpressed. In vitro studies indicated that the route to R-1,2-PD involved the reduction of methylglyoxal to R-lactaldehyde by the recombinant glycerol dehydrogenase and the reduction of R-lactaldehyde to R-1, 2-PD by a native E. coli activity. We expect that R-1,2-PD production can be significantly improved through further metabolic and bioprocess engineering.

FIG. 1

Time course of two sets of 150-ml anaerobic batch fermentations of E. coli carrying pNEA30 expressing the genes for E. coli glycerol dehydrogenase (gldA) and E. coli MG synthase (mgs). Concentrations in the flasks are shown for glucose (■), 1,2-PD (●), and cells as optical density (▾) with no IPTG addition and for glucose (□), 1,2-PD (○), and cells as optical density (▿) with 0.1 mM IPTG added at 12 h after inoculation. Error bars are standard deviations of three replicates.

FIG. 2

Metabolic pathways to the enantiomers of 1,2-PD from the common precursor MG. In our engineered pathway, MG synthase converts DHAP to MG, which is then reduced to R-lactaldehyde by glycerol dehydrogenase. A native E. coli enzyme is responsible for the reduction of R-lactaldehyde to R-1,2-PD. ∗, possible activity, but not yet reported in literature.