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Pyruvate Formate Lyase and Acetate Kinase Are Essential for Anaerobic Growth of Escherichia coli on Xylose
Adnan Hasona, Youngnyun Kim, F. G. Healy, L. O. Ingram and K. T. Shanmugam J. Bacteriol. 2004, 186(22):7593. DOI: 10.1128/JB.186.22.7593-7600.2004.

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JOURNAL OF BACTERIOLOGY, Nov. 2004, p. 7593–7600 0021-9193/04/$08.00 0 DOI: 10.1128/JB.186.22.7593–7600.2004 Copyright © 2004, American Society for Microbiology. All Rights Reserved.

Vol. 186, No. 22

Pyruvate Formate Lyase and Acetate Kinase Are Essential for Anaerobic Growth of Escherichia coli on Xylose†
AdnanHasona,‡ Youngnyun Kim, F. G. Healy,§ L. O. Ingram, and K. T. Shanmugam*
Department of Microbiology and Cell Science, University of Florida, Gainesville, Florida 32611
Received 21 May 2004/Accepted 16 August 2004

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During anaerobic growth of bacteria, organic intermediates of metabolism, such as pyruvate or itsderivatives, serve as electron acceptors to maintain the overall redox balance. Under these conditions, the ATP needed for cell growth is derived from substrate-level phosphorylation. In Escherichia coli, conversion of glucose to pyruvate yields 2 net ATPs, while metabolism of a pentose, such as xylose, to pyruvate only yields 0.67 net ATP per xylose due to the need for one (each) ATP for xylosetransport and xylulose phosphorylation. During fermentative growth, E. coli produces equimolar amounts of acetate and ethanol from two pyruvates, and these reactions generate one additional ATP from two pyruvates (one hexose equivalent) while still maintaining the overall redox balance. Conversion of xylose to acetate and ethanol increases the net ATP yield from 0.67 to 1.5 per xylose. An E. coli pflmutant lacking pyruvate formate lyase cannot convert pyruvate to acetyl coenzyme A, the required precursor for acetate and ethanol production, and could not produce this additional ATP. E. coli pfl mutants failed to grow under anaerobic conditions in xylose minimal medium without any negative effect on their survival or aerobic growth. An ackA mutant, lacking the ability to generate ATP from acetylphosphate, also failed to grow in xylose minimal medium under anaerobic conditions, confirming the need for the ATP produced by acetate kinase for anaerobic growth on xylose. Since arabinose transport by AraE, the low-affinity, high-capacity, arabinose/H symport, conserves the ATP expended in pentose transport by the ABC transporter, both pfl and ackA mutants grew anaerobically with arabinose.AraE-based xylose transport, achieved after constitutively expressing araE, also supported the growth of the pfl mutant in xylose minimal medium. These results suggest that a net ATP yield of 0.67 per pentose is only enough to provide for maintenance energy but not enough to support growth of E. coli in minimal medium. Thus, pyruvate formate lyase and acetate kinase are essential for anaerobic growth ofE. coli on xylose due to energetic constraints. All living systems generate the needed energy for cell maintenance and growth by catalyzing a set of coupled oxidationreduction reactions. A critical component of these oxidationreduction reactions is the redox balance of the sum of all metabolic reactions. With external input of an oxidant, such as dioxygen, the carbon and energy source can be...