Effect of nitrogen oxides on expression of the nir and nor genes for denitrification in Pseudomonas aeruginosa

The activity of the promoters involved in transcription of the genes (nirS, nirQ</it> and norC</it>) required for anaerobic reduction of nitrite and nitric oxide was investigated in NIR- and NOR-deficient mutants of Pseudomonas aeruginosa</it>. The transcriptional activity of these three promoters was induced by nitrite in a wild-type strain and the activity was low in an nirS</it> mutant. In norCBD</it> and nirQOP</it> mutants, which were expected to accumulate nitric oxide because of a lack of nitric oxide reductase activity, the norC</it> and nirQ</it> promoters showed significantly enhanced activity in promoting transcription relative to the parental strain, even at low nitrite concentrations. These results suggest that the nirQ</it> and norC</it> promoters are regulated by the concentration of endogenous nitric oxide rather than that of nitrite.