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Diversion of the Metabolic Flux from Pyruvate Dehydrogenase to Pyruvate Oxidase Decreases Oxidative Stress during Glucose Metabolism in Nongrowing Escherichia coli Cells Incubated under Aerobic, Phosphate Starvation Conditions

Laboratoire de Chimie Bactérienne, Centre National de la Recherche Scientifique, 13009 Marseille, France

Received 10 May 2004/ Accepted 26 July 2004

Ongoing aerobic metabolism in nongrowing cells may generate oxidative stress. It is shown here that the levels of thiobarbituric acid-reactive substances (TBARSs), which measure fragmentation products of oxidized molecules, increased strongly at the onset of starvation for phosphate (P_i). This increase in TBARS levels required the activity of the histone-like nucleoid-structuring (H-NS) protein. TBARS levels weakly increased further in ahpCF mutants deficient in alkyl hydroperoxide reductase (AHP) activity during prolonged metabolism of glucose to acetate. Inactivation of pyruvate oxidase (PoxB) activity decreased the production of acetate by half and significantly increased the production of TBARS. Overall, these data suggest that during incubation under aerobic, P_i starvation conditions, metabolic flux is diverted from the pyruvate dehydrogenase (PDH) complex (NAD dependent) to PoxB (NAD independent). This shift may decrease the production of NADH and in turn the adventitious production of H₂O₂ by NADH dehydrogenase in the respiratory chain. The residual low levels of H₂O₂ produced during prolonged incubation can be scavenged efficiently by AHP. However, high levels of H₂O₂ may be reached transiently at the onset of stationary phase, primarily because H-NS may delay the metabolic shift from PDH to PoxB.

This paper is dedicated to the memory of Benjamin Moreau (1977-2000).

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