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Proc Natl Acad Sci U S A. 2009 Dec 1;106(48):20180-5. doi: 10.1073/pnas.0905396106. Epub 2009 Nov 16.

Metabolic evolution of energy-conserving pathways for succinate production in Escherichia coli.

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  • 1Department of Microbiology and Cell Science, University of Florida, Gainesville, FL 32611, USA.

Abstract

During metabolic evolution to improve succinate production in Escherichia coli strains, significant changes in cellular metabolism were acquired that increased energy efficiency in two respects. The energy-conserving phosphoenolpyruvate (PEP) carboxykinase (pck), which normally functions in the reverse direction (gluconeogenesis; glucose repressed) during the oxidative metabolism of organic acids, evolved to become the major carboxylation pathway for succinate production. Both PCK enzyme activity and gene expression levels increased significantly in two stages because of several mutations during the metabolic evolution process. High-level expression of this enzyme-dominated CO(2) fixation and increased ATP yield (1 ATP per oxaloacetate). In addition, the native PEP-dependent phosphotransferase system for glucose uptake was inactivated by a mutation in ptsI. This glucose transport function was replaced by increased expression of the GalP permease (galP) and glucokinase (glk). Results of deleting individual transport genes confirmed that GalP served as the dominant glucose transporter in evolved strains. Using this alternative transport system would increase the pool of PEP available for redox balance. This change would also increase energy efficiency by eliminating the need to produce additional PEP from pyruvate, a reaction that requires two ATP equivalents. Together, these changes converted the wild-type E. coli fermentation pathway for succinate into a functional equivalent of the native pathway that nature evolved in succinate-producing rumen bacteria.

PMID:
19918073
[PubMed - indexed for MEDLINE]
PMCID:
PMC2777959
Free PMC Article

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