Identification of the sources of nitrous oxide produced by oxidative and reductive processes in Nitrosomonas europaea

Abstract

1. Cells of Nitrosomonas europaea produced N₂O during the oxidation of ammonia and hydroxylamine. 2. The end-product of ammonia oxidation, nitrite, was the predominant source of N₂O in cells. 3. Cells also produced N₂O, but not N₂ gas, by the reduction of nitrite under anaerobic conditions. 4. Hydroxylamine was oxidized by cell-free extracts to yield nitrite and N₂O aerobically, but to yield N₂O and NO anaerobically. 5. Cell extracts reduced nitrite both aerobically and anaerobically to NO and N₂O with hydroxylamine as an electron donor. 6. The relative amounts of NO and N₂O produced during hydroxylamine oxidation and/or nitrite reduction are dependent on the type of artificial electron acceptor utilized. 7. Partially purified hydroxylamine oxidase retained nitrite reductase activity but cytochrome oxidase was absent. 8. There is a close association of hydroxylamine oxidase and nitrite reductase activities in purified preparations.