2-25: Microaerobic conversion of glycerol to ethanol by Escherichia coli

Glycerol has become a desirable feedstock for the production of fuels and chemicals due to its availability and low price.  We have developed a strain and process for the efficient microaerobic conversion of glycerol to ethanol by Escherichia coli using only E. coli genes.  To increase yield, we eliminated glycerol-utilizing pathways that produce byproducts such as acetate, succinate, and lactate.  To increase the rate, titer, and specific activity, we up-regulated glycerol uptake genes dhaKLM, gldA, and glpK, as well as the ethanol pathway gene adhE.  The final strain is able to produce 46.5 g/L of ethanol in 45 hours with 87% of theoretical yield.  The specific activity of the strain is 1.16 mmol/L/h/OD.   This represents the best reported productivity for the production of ethanol from crude glycerol, a sustainable, renewable, non-food alternative to sugar-based ethanol fermentations.