Sunday, July 29, 2007
P103
Engineering a Native Homoethanol Pathway in Escherichia coli B for Ethanol Production
Shengde Zhou, A. G. Iverson, and W. S. Grayburn. Biological Sciences, Northern Illinois University, DeKalb, IL 60115
The microbial production of cellulosic ethanol has the potential to offer a sustainable, renewable, and environmental friendly transportation fuel. To realize this potential, multiple recombinant bacterial and yeast strains have been developed for conversion of biomass derived hexose (C6) and pentose (C5) sugars into ethanol. However, foreign genes and/or promoters were recruited for pentose metabolism and/or ethanol production in those recombinant microorganisms. Using a novel approach, we engineered a native homoethanol pathway in Escherichia coli B without adding foreign genes and/or promoters. The competing pathways were eliminated by chromosomal deletions of genes encoding fumarate reductase (frdABCD), lactate dehydrogenase (ldhA), acetate kinase (ackA), and pyruvate formate lyase (pflB). For redox balance, the pyruvate dehydrogenase operon (aceEF-lpd, a typical aerobically-expressed operon) was highly expressed anaerobically through transcriptional fusion. The native homoethanol pathway was established through the anaerobically expressed pyruvate dehydrogenase complex (oxidization of pyruvate to acetyl-CoA) and the fermentative alcohol dehydrogenase (reduction of acetyl-CoA to ethanol). The resulting strain SZ420 efficiently ferments glucose and xylose into ethanol with a yield of 90% under anaerobic conditions.
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