Ammonium transformed into nitrous oxide via nitric oxide by Pseudomonas putida Y-9 under aerobic conditions without...

Previous studies have reported that hydroxylamine (NH₂OH) is an inevitable intermediate of the ammonium (NH₄⁺) oxidation pathway under aerobic conditions. In this study, Pseudomonas putida Y-9 was found to oxidize ammonium into N₂O via NO without the accumulation of NH₂OH and NO₂^- under aerobic conditions. NH₂OH was nearly completely transformed into NO₂^- whether NH₄⁺ was present in the medium, and NH₄⁺ could accelerate the transformation of NH₂OH to NO₂^- by promoting Y-9 growth. NH₄⁺ was oxidized rapidly by Y-9 with or without the presence of NH₂OH in the medium, and the decrease of total nitrogen reached 30.65 mg/L and 39.38 mg/L, respectively, which indicates that NH₂OH inhibits the transformation efficiency of NH₄⁺ to N₂O. Gene amplification and enzyme assays demonstrated that ammonia monooxygenase doesn't exist in Y-9. All results show that NH₄⁺ can be transformed into N₂O via NO by Y-9 under aerobic conditions without NH₂OH as intermediate.