Metabolic engineering of Escherichia coli for the production of 1,2-propanediol from glycerol.

Due to its availability, low-price, and high degree of reduction, glycerol has become an attractive carbon source for the production of fuels and reduced chemicals. Using the platform we have established from the identification of key pathways mediating fermentative metabolism of glycerol, this work reports the engineering of Escherichia coli for the conversion of glycerol into 1,2-propanediol (1,2-PDO). A functional 1,2-PDO pathway was engineered through a combination of overexpression of genes involved in its synthesis from the key intermediate dihydroxyacetone phosphate (DHAP) and the manipulation of the fermentative glycerol utilization pathway. The former included the overexpression of methylglyoxal synthase (mgsA), glycerol dehydrogenase (gldA), and aldehyde oxidoreductase (yqhD). Manipulation of the glycerol utilization pathway through the replacement of the native E. coli PEP-dependent dihydroxyacetone kinase (DHAK) with an ATP-dependent DHAK from C. freundii increased the availability of DHAP allowing for higher 1,2-PDO production. Analysis of the major fermentative pathways identified ethanol as a required co-product while increases in 1,2-PDO titer and yield were achieved through the disruption of the pathways for acetate and lactate production. Combination of these key metabolic manipulations resulted in an engineered E. coli strain capable of producing 5.6 g/L 1,2-PDO, at a yield of 21.3% (w/w). This strain also performed well when crude glycerol, a by-product of biodiesel production, was used as the substrate. The titer and yield achieved in this study were favorable to those obtained with the use of E. coli for the production of 1,2-PDO from common sugars.