METABOLISM OF NITRIC-OXIDE IN DENITRIFYING PSEUDOMONAS-AERUGINOSA AND NITRATE-RESPIRING BACILLUS-CEREUS

Suspensions of Pseudomonas aeruginosa and Bacillus cereus were continuously sparged with nitrogen to remove gaseous products of nitrate reduction. Under these conditions, P. aeruginosa denitrified nitrate to 4% NO, 47% N2O and 49% N2. B. cereus reduced nitrate to 94% nitrite, 2% NO and 5% N2O. B. cereus was unable to reduce NO or N2O as sole electron acceptor, whereas P. aeruginosa reduced NO stoichiometrically to N2O when the N2O reductase was inhibited by acetylene or when the formed N2O was immediately flushed out of the incubation vessel. The mechanism and the reason for NO production in nitrate-respiring B. cereus are unknown, but the amounts of NO released were in a similar range as in the denitrifying P. aeruginosa and thus may be of similar environmental importance.