Transcriptional regulation of the nos genes for nitrous oxide reductase in Pseudomonas aeruginosa

The genes for nitrous oxide (N2O) reduction, nosRZDFYL, are clustered on the chromosome of Pseudomonas aeruginosa. Promoter assays using transcriptional fusions to lacZ revealed that the structural gene for nitrous oxide reductase, nosZ, is transcribed with the upstream nosR gene. The nosR gene product is not required for the activity of the nosR promoter. A sequence similar to the consensus FNR-binding motif was found 41(.)5 bp upstream from the major transcriptional start point of nosR. Mutation of the motif significantly reduced the promoter activity. DNR, an FNR-related transcriptional regulator required for the expression of denitrification genes in P. aeruginosa, is necessary for the transcription of nosR, indicating that the motif is recognized by DNR. Nitrite (NO2-), nitric oxide (NO) and NO-generating reagents induced nosR promoter activity, but N2O did not. The NO2--induced nosR promoter activity was reduced by mutation of the NO2- reductase mutant. These results indicate that NO is the inducer molecule for transcription of the nos genes.