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Applied and Environmental Microbiology, January 2007, p. 456-464, Vol. 73, No. 2
0099-2240/07/$08.00+0     doi:10.1128/AEM.02022-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Homolactate Fermentation by Metabolically Engineered Escherichia coli Strains{triangledown}

Y. Zhu, M. A. Eiteman,* K. DeWitt, and E. Altman

Center for Molecular BioEngineering, Department of Biological and Agricultural Engineering, University of Georgia, Athens, Georgia 30602

Received 25 August 2006/ Accepted 13 November 2006

We report the homofermentative production of lactate in Escherichia coli strains containing mutations in the aceEF, pfl, poxB, and pps genes, which encode the pyruvate dehydrogenase complex, pyruvate formate lyase, pyruvate oxidase, and phosphoenolpyruvate synthase, respectively. The process uses a defined medium and two distinct fermentation phases: aerobic growth to an optical density of about 30, followed by nongrowth, anaerobic production. Strain YYC202 (aceEF pfl poxB pps) generated 90 g/liter lactate in 16 h during the anaerobic phase (with a yield of 0.95 g/g and a productivity of 5.6 g/liter · h). Ca(OH)2 was found to be superior to NaOH for pH control, and interestingly, significant succinate also accumulated (over 7 g/liter) despite the use of N2 for maintaining anaerobic conditions. Strain ALS961 (YYC202 ppc) prevented succinate accumulation, but growth was very poor. Strain ALS974 (YYC202 frdABCD) reduced succinate formation by 70% to less than 3 g/liter. 13C nuclear magnetic resonance analysis using uniformly labeled acetate demonstrated that succinate formation by ALS974 was biochemically derived from acetate in the medium. The absence of uniformly labeled succinate, however, demonstrated that glyoxylate did not reenter the tricarboxylic acid cycle via oxaloacetate. By minimizing the residual acetate at the time that the production phase commenced, the process with ALS974 achieved 138 g/liter lactate (1.55 M, 97% of the carbon products), with a yield of 0.99 g/g and a productivity of 6.3 g/liter · h during the anaerobic phase.

* Corresponding author. Mailing address: Center for Molecular BioEngineering, Department of Biological and Agricultural Engineering, University of Georgia, Athens, GA 30602. Phone: (706) 542-0833. Fax: (706) 542-8806. E-mail: eiteman{at}engr.uga.edu.

{triangledown} Published ahead of print on 22 November 2006.

Applied and Environmental Microbiology, January 2007, p. 456-464, Vol. 73, No. 2
0099-2240/07/$08.00+0     doi:10.1128/AEM.02022-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Zhu, Y., Eiteman, M. A., Altman, R., Altman, E. (2008). High Glycolytic Flux Improves Pyruvate Production by a Metabolically Engineered Escherichia coli Strain. Appl. Environ. Microbiol. 74: 6649-6655 [Abstract] [Full Text]  


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