Pathway of nitrous oxide consumption in isolated P seudomonas stutzeri strains under anoxic and oxic conditions.

The microbial consumption of nitrous oxide ( N₂O) has gained great interest since it was revealed that this process could mitigate the greenhouse effect of N₂O. The consumption of N₂O results from its reduction to dinitrogen gas ( N₂) as part of the denitrification process. However, there is ongoing debate regarding an alternative pathway, namely reduction of N₂O to NH₄⁺, or assimilatory N₂O consumption. To date, this pathway is poorly investigated and lacks unambiguous evidence. Enrichment of denitrifying activated sludge using a mineral nitrogen-free medium rendered a mixed culture capable of anoxic and oxic N₂O consumption. Dilution plating, isolation and deoxyribonucleic acid fingerprinting identified a collection of P seudomonas stutzeri strains as dominant N₂O consumers in both anaerobic and aerobic enrichments. A detailed isotope tracing experiment with a P seudomonas stutzeri isolate showed that consumption of N₂O via assimilatory reduction to NH₄⁺ was absent. Conversely, respiratory N₂O reduction was directly coupled to N₂ fixation. [ABSTRACT FROM AUTHOR]