Physiological and Molecular Biological Characterization of Ammonia Oxidation of the Heterotrophic Nitrifier Pseudomonas putida

Abstract.

The heterotrophic nitrifier Pseudomonas putida aerobically oxidized ammonia to hydroxylamine, nitrite, and nitrate. Product formation was accompanied by a small but significant release of NO, whereas N₂O evolution could not be detected under the assay conditions employed. The isolate reduced nitrate to nitrite and partially further to NO under anaerobic conditions. Aerobically grown cells utilized γ-aminobutyrate as a carbon source and as a N-source by ammonification. The physiological experiments, in particular the inhibition pattern by C₂H₂, indicated that P. putida expressed an ammonia monooxigenase. DNA-hybridization with an amoA gene probe coding for the smaller subunit of the ammonia monooxigenase of Nitrosomonas europaea allowed us to identify, to clone, and to sequence a region with an open reading frame showing distinct sequence similarities to the amoA gene of autotrophic ammonia oxidizers.