Diversity of oxygen and N-oxide regulation of nitrite reductases in denitrifying bacteria

We examined alpha, beta and gamma Proteobacteria with Cu and heme-type dissimilatory nitrite reductases for patterns of nir regulation. Six of seven strains expressed nitrite reductase under aerobic growth conditions. In only one strain, G-179, was it stringently regulated by O-2. Growth with NO3- or NO2- enhanced nitrite reductase production in four of seven strains under anaerobic growth conditions, but in only one strain, Pseudomonas aeruginosa PA01, under aerobic conditions. In this strain the nitrite reductase production was primarily regulated by an ani gene when grown under anaerobic conditions, but when grown under aerobic conditions it was regulated by both an ani gene and nitrogen oxide. Constitutive production of nitrite reductase was a common phenomenon rather than the exception among denitrifiers from the environment, which helps explain the prevalence of denitrifying enzymes in aerobic soils.