Nitrite-Dependent Anaerobic Methane Oxidizing Bacteria In Tibetan Plateau

Nitrite-dependent anaerobic methane oxidation（N-DAMO）is a microbial process linking the global carbon and nitrogen cycles that is catalysed by Candidatus Methylomirabilis oxyfera.This process was reported to oxidize methane（CH₄）to carbon dioxide（CO₂）using nitrite（NO₂^-）as an electron acceptor,which is of great importance to carbon and nitrogen cycling.To the best of our knowledge,the presence,abundance,diversity and activity of M.oxyfera-like bacteria in Tibetan grassland soils have not been documented.In the present study,the abundance,diversity and activity of M.oxyfera-like bacteria in soils from swamp meadow,alpine meadow and alpine steppe in the Qinghai-Tibet Plateau were analyzed by the N-DAMO bacterial targeting 16S rDNA quantitative PCR,Hi-Seq high-throughput sequencing and stable isotope activity tracing microcosm experiments.The main research results were described as the following:1、This study demonstrated for the first time the existence of M.oxyfera-like bacteria in the Tibetan Plateau.The abundance of M.oxyfera-like bacteria in the soils of the Qinghai-Tibet Plateau ranged from 1.65±0.38×10⁵-3.20±0.49×10⁶ copies·g^-11 dry weight.There was a significant negative correlations between the abundance of M.oxyfera-like bacteria and NO₃^-,NH₄⁺,NO₂^-and TIN contents in soils（r=-0.488,P<0.01;r=-0.351,P<0.05;r=-0.364,P<0.05and r=-0.398,P<0.05）.2、The sequencing results showed that the 16S rRNA gene sequence of N-DAMO strain was closely related to the known M.oxyfera strain with a similarity of 95%to 100%,the sequence of the NC10 phylum belonging to M.oxyfera strain accounted for 97.37%of the total number of sequences.But there were only a few bacterial species that are closely related to M.oxyfera in the Tibetan Plateau ecosystem,indicating the N-DAMO bacterial population diversity was not high.The correlation analysis of environmental factors and diversity showed that the composition of M.oxyfera-like bacteria was positively correlated with NO₃^-and TIN contents in soils（r=0.930,P<0.01 and r=0.910,P<0.05）.3、The stable isotope activity tracer experiments had detected ¹³CO₂ content and soil ¹³C abundance increase in swamp meadow and alpine meadow soils,respectively.It showed that the N-DAMO reaction was an important part of the carbon and nitrogen cycle and a potential methane sink in the studied area.Pearson correlation analysis showed that there was a significant negative correlation between ¹³CO₂ atomic percent（%）and OC and NO₃^-contents（r=-0.854,P<0.05;r=-0.998,P<0.05）,soil ¹³C abundance（%）was significantly negatively correlated with OC content（r=-0.849,P<0.05）.