Conversion of Glucose and Gluconate to Ethanol in Mineral Salts Medium using Recombinant Escherichia coli Strains

Escherichia coli AH003, a derivative of E. coli KO11 with the L-lactate dehydrogenase (ldh) and pyruvate formate lyase (pfl) genes deleted and its parent strain E. coli KO11 were used as the ethanologen to convert glucose and gluconate to ethanol in M9 minimal medium. E. coli AH003 grew very poorly on glucose in M9 medium. However it achieved rapid growth when gluconate was used as the carbon source. The addition of gluconate to medium containing glucose improved the rate of glucose utilization. In contrast, E. coli KO11 grew well on both glucose and gluconate in M9 medium. The addition of gluconate to medium containing glucose did not improve the rate of glucose utilization. We believe that the deletion of the pfl gene in E. coli AH003 led to the different fermentation results. The co-fermentation of gluconate and glucose could be a useful strategy to improve the rate of glucose fermentation and decrease nutrient requirements for engineered strains lacking the pfl gene and grown under anaerobic conditions.