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Escherichia coli , a facultative aerobe, expresses two distinct respiratory nitrate reductases. The periplasmic NapABC enzyme likely functions during growth in nitrate-limited environments, whereas the membrane-bound NarGHI enzyme functions during growth in nitrate-rich environments. Maximal expression of thenapFDAGHBC operon encoding periplasmic nitrate reductase results from synergistic transcription activation by the Fnr and phospho-NarP proteins, acting in response to anaerobiosis and nitrate or nitrite, respectively. Here, we report that, during anaerobic growth with no added nitrate, less-preferred carbon sources stimulatednapF operon expression by as much as fourfold relative to glucose. Deletion analysis identified a cyclic AMP receptor protein (Crp) binding site upstream of the NarP and Fnr sites as being required for this stimulation. ThenapD andnrfA operon control regions fromShewanella spp. also have apparent Crp and Fnr sites, and expression from theShewanella oneidensis nrfA control region cloned inE. coli was subject to catabolite repression. In contrast, the carbon source had relatively little effect on expression of thenarGHJI operon encoding membrane-bound nitrate reductase under any growth condition tested. Carbon source oxidation state had no influence on synthesis of either nitrate reductase. The results suggest that the Fnr and Crp proteins may act synergistically to enhance NapABC synthesis during growth with poor carbon sources to help obtain energy from low levels of nitrate.

Catabolite Repression Control ofnapF(Periplasmic Nitrate Reductase) Operon Expression inEscherichia coliK-12