The Occurrence of Putative Nitric Oxide Dismutase (Nod) in an Alpine Wetland with a New Dominant Subcluster and the Potential Ability for a Methane Sink.

Recently, a new oxygenic pathway has been proposed based on the disproportionation of NO with putative NO dismutase (Nod). In addition to a new process in nitrogen cycling, this process provides ecological advantages for the degradation of substrates in anaerobic conditions, which is of great significance for wastewater treatment. However, the Nod distribution in aquatic environments is rarely investigated. In this study, we obtained the nod genes with an abundance of 2.38 ± 0.96 × 10⁵ copies per gram of dry soil from the Zoige wetland and aligned the molecular characteristics in the corresponding Nod sequences. These Nod sequences were not only found existing in NC10 bacteria, but were also found forming some other clusters with Nod sequences from a WWTP reactor or contaminated aquifers. Moreover, a new subcluster in the aquifer-similar cluster was even dominant in the Zoige wetland and was named the Z-aquifer subcluster. Additionally, soils from the Zoige wetland showed a high potential rate (10.97 ± 1.42 nmol of CO₂ per gram of dry soil per day) for nitrite-dependent anaerobic methane oxidation (N-DAMO) with low abundance of NC10 bacteria, which may suggest a potential activity of Nod in other clusters when considering the dominance of the Z-aquifer subcluster Nod. In conclusion, we verified the occurrence of Nod in an alpine wetland for the first time and found a new subcluster to be dominant in the Zoige wetland. Moreover, this new subcluster of Nod may even be active in the N-DAMO process in this alpine wetland, which needs further study to confirm.