Engineering a native homoethanol pathway in Escherichia coli B for ethanol production

A native homoethanol pathway (pyruvate-to-acetyl-CoA-to-acetaldehyde-to-ethanol) was engineered in Escherichia coli B. The competing fermentation pathways were eliminated by chromosomal deletions of the genes encoding for fumarate reductase (frdABCD), lactate dehydrogenase (ldhA), acetate kinase (ackA), and pyruvate formate lyase (pflB). For redox balance and anaerobic cell growth, the pyruvate dehydrogenase complex (aceEF-lpd, a typical aerobically-expressed operon) was highly expressed anaerobically using a native anaerobic inducible promoter. The resulting strain SZ420 (ΔfrdBC ΔldhA ΔackA ΔfocA-pflB ΔpdhR::pflBp6-pflBrbs-aceEF-lpd) contains no foreign genes and/or promoters and efficiently ferments glucose and xylose into ethanol with a yield of 90% under anaerobic conditions.