Anaerobic methane oxidation coupled to nitrite reduction can be a potential methane sink in coastal environments

In the current study, we investigated nitrite-dependent anaerobic methane oxidation (N-DAMO) as a potential methane sink in the Hangzhou Bay and the adjacent Zhoushan sea area. The potential activity of the N-DAMO process was primarily observed in Hangzhou Bay by means of 13 C-labeling experiments, whereas very low or no potential N-DAMO activity could be detected in the Zhoushan sea area. The measured potential N-DAMO rates ranged from 0.2 to 1.3 nmol 13 CO 2 g −1 (dry sediment) day −1 , and the N-DAMO potentially contributed 2.0–9.4 % to the total microbial methane oxidation in the examined sediments. This indicated that the N-DAMO process may be an alternative pathway in the coastal methane cycle. Phylogenetic analyses confirmed the presence of Candidatus Methylomirabilis oxyfera -like bacteria in all the examined sediments, while the group A members (the dominant bacteria responsible for N-DAMO) were found mainly in Hangzhou Bay. Quantitative PCR showed that the 16S rRNA gene abundance of Candidatus M. oxyfera -like bacteria varied from 5.4 × 10 6 to 5.0 × 10 7 copies g −1 (dry sediment), with a higher abundance observed in Hangzhou Bay. In addition, the overlying water NO 3 − concentration and salinity were identified as the most important factors influencing the abundance and potential activity of Candidatus M. oxyfera -like bacteria in the examined sediments. This study showed the evidence of N-DAMO in coastal environments and indicated the importance of N-DAMO as a potential methane sink in coastal environments.