PHYSIOLOGICAL AND MOLECULAR BIOLOGICAL CHARACTERIZATION OF AMMONIA OXIDATION OF THE HETEROTROPHIC NITRIFIER PSEUDOMONAS-PUTIDA

The heterotrophic nitrifier Pseudomonas putida aerobically oxidized am monia to hydroxylamine, nitrite, and nitrate. Product formation was ac companied by a small but significant release of NO, whereas N2O evolut ion could not be detected under the assay conditions employed. The iso late reduced nitrate to nitrite and partially further to NO under anae robic conditions. Aerobically grown cells utilized gamma-aminobutyrate as a carbon source and as a N-source by ammonification, The physiolog ical experiments, in particular the inhibition pattern by C2H2, indica ted that P. putida expressed an ammonia monooxigenase, DNA-hybridizati on with an amoA gene probe coding for the smaller subunit of the ammon ia monooxigenase of Nitrosomonas europaea allowed us to identify, to c lone, and to sequence a region with an open reading frame showing dist inct sequence similarities to the amoA gene of autotrophic ammonia oxi dizers.