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Appl. Environ. Microbiol. doi:10.1128/AEM.02708-07
Copyright (c) 2008, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

A Minimal Escherichia coli Cell for most Efficient Ethanol Production from Hexoses and Pentoses

Department of Chemical Engineering and Materials Science, and BioTechnology Institute, University of Minnesota, 240 Gortner Laboratory, 1479 Gortner Ave, St. Paul, MN 55108, USA

^* To whom correspondence should be addressed. Email: srienc{at}umn.edu.

	Abstract

To obtain an efficient ethanologenic E. coli strain we have reduced with 8 gene knockout mutations the functional space of the central metabolism from over 15,000 pathway possibilities to six pathway options that support cell function. The remaining pathways, identified by elementary mode analysis, consist of 4 pathways with non- growth associated conversion of pentoses and hexoses into ethanol at theoretical yields, and 2 pathways with tight coupling of anaerobic cell growth with ethanol formation at high yield. Elimination of three additional genes results in a strain that selectively grows only on pentoses even in the presence of glucose with high ethanol yield. We show that the strains with minimized metabolic functionality closely match the theoretical predictions. Remarkably, catabolite repression is completely absent during anaerobic growth resulting in simultaneous utilization of pentoses and hexoses for ethanol production.