ANAEROBIC ACTIVATION OF THE ENTIRE DENITRIFICATION PATHWAY IN PSEUDOMONAS-AERUGINOSA REQUIRES ANR, AN ANALOG OF FNR

The Pseudomonas aeruginosa gene anr, which encodes a structural and fu nctional analog of the anaerobic regulator Fnr in Escherichia coli, wa s mapped to the SpeI fragment R, which is at about 59 min on the genom ic map of P. aeruginosa PAO1. Wild-type P. aeruginosa PAO1 grew under anaerobic conditions with nitrate, nitrite, and nitrous oxide as alter native electron accepters. An anr deletion mutant, PAO6261, was constr ucted. It was unable to grow with these alternative electron accepters ; however, its ability to denitrify was restored upon the introduction of the wild-type anr gene. In addition, the activities of two enzymes in the denitrification pathway, nitrite reductase and nitric oxide re ductase, were not detectable under oxygen-limiting conditions in strai n PAO6261 but were restored when complemented with the anr(+) gene. Th ese results indicate that the anr gene product plays a key role in ana erobically activating the entire denitrification pathway.