Effects of limited aeration and of the ArcAB system on intermediary pyruvate catabolism in Escherichia coli

The capacity of Escherichia coli to adapt its catabolism to prevailing redo x conditions resides mainly in three catabolic branch points involving (i) pyruvate formate-lyase (PFL) and the pyruvate dehydrogenase complex (PDHc), (ii) the exclusively fermentative enzymes and those of the Krebs cycle, an d (iii) the alternative terminal cytochrome bd and cytochrome bo oxidases. A quantitative analysis of the relative catabolic fluxes through these path ways is presented for steady-state glucose-limited chemostat cultures with controlled oxygen availability ranging from full aerobiosis to complete ana erobiosis. Remarkably, Pn contributed significantly to the catabolic flux u nder microaerobic conditions and was found to be active simultaneously with PDHc and cytochrome bd oxidase-dependent respiration. The synthesis of PFL and cytochrome bd oxidase was found to be maximal in the lower microaerobi c range but not in a Delta ArcA mutant, and we conclude that the Are system is more active with respect to regulation of these two positively regulate d operons during microaerobiosis than during anaerobiosis.