Oxygen, nitrate, and molybdenum regulation of dmsABC gene expression in Escherichia coli

Escherichia coli can respire anaerobically using either trimethylamine-N-oxide (TMAO) or dimethyl sulfoxide (DMSO) as the terminal electron acceptor for oxidative phosphorylation. To determine whether the regulation of the dmsABC genes, which encode a membrane-associated TMAO/DMSO reductase, are transcriptionally controlled in response to the availability of alternate electron acceptors, we constructed an operon fusion between the dmsA gene, along with its associated regulatory region, and lacZ+. Expression of dmsA'-lacZ was stimulated 65-fold by anaerobiosis versus aerobiosis, while nitrate caused a 12-fold repression. Its expression, however, was unaffected by the presence of the alternate electron acceptors DMSO, TMAO, and fumarate. Anaerobic induction of dmsA'-lacZ was defective in an fnr mutant, thus establishing that Fnr is responsible for anaerobic activation of dmsABC. Repression of dmsA'-lacZ expression by nitrate was independent of oxygen and was shown to be mediated by the products of two genes, narL (frdR2) and narX. dmsA'-lacZ expression was also altered in chlD strains that are defective in molybdenum transport but not in chlA and chlE strains that are defective in molybdopterin cofactor biosynthesis, thus establishing that the molybdenum ion but not the ability to form a functional cofactor is required for regulation. Molybdenum was required both for complete induction of dmsA'-lacZ expression during anaerobic growth and for complete repression of dmsA'-lacZ by nitrate. Additionally, expression of dmsABC varied depending on the carbon source. Expression was highest when cells were grown on sorbitol.