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Applied and Environmental Microbiology, June 2008, p. 3634-3643, Vol. 74, No. 12
0099-2240/08/$08.00+0     doi:10.1128/AEM.02708-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Minimal Escherichia coli Cell for the Most Efficient Production of Ethanol from Hexoses and Pentoses{triangledown} ,{dagger}

Cong T. Trinh,1,2 Pornkamol Unrean,1,2 and Friedrich Srienc1,2*

Department of Chemical Engineering and Materials Science,1 BioTechnology Institute, University of Minnesota, 240 Gortner Laboratory, 1479 Gortner Avenue, St. Paul, Minnesota 551082

Received 30 November 2007/ Accepted 8 April 2008

To obtain an efficient ethanologenic Escherichia coli strain, we reduced the functional space of the central metabolic network, with eight gene knockout mutations, from over 15,000 pathway possibilities to 6 pathway options that support cell function. The remaining pathways, identified by elementary mode analysis, consist of four pathways with non-growth-associated conversion of pentoses and hexoses into ethanol at theoretical yields and two pathways with tight coupling of anaerobic cell growth with ethanol formation at high yields. Elimination of three additional genes resulted in a strain that selectively grows only on pentoses, even in the presence of glucose, with a high ethanol yield. We showed that the ethanol yields of strains with minimized metabolic functionality closely matched the theoretical predictions. Remarkably, catabolite repression was completely absent during anaerobic growth, resulting in the simultaneous utilization of pentoses and hexoses for ethanol production.

* Corresponding author. Mailing address: BioTechnology Institute, University of Minnesota, 240 Gortner Laboratory, 1479 Gortner Avenue, St. Paul, MN 55108. Phone: (612) 624-9776. Fax: (612) 625-1700. E-mail: srienc{at}umn.edu

{triangledown} Published ahead of print on 18 April 2008.

{dagger} Supplemental material for this article may be found at http://aem.asm.org/.

Applied and Environmental Microbiology, June 2008, p. 3634-3643, Vol. 74, No. 12
0099-2240/08/$08.00+0     doi:10.1128/AEM.02708-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.





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