Spatio-temporal variations of activity of nitrate-driven anaerobic oxidation of methane and community structure of Candidatus Methanoperedens-like archaea in sediment of Wuxijiang river

Nitrate-driven anaerobic oxidation of methane (AOM), catalyzing by Candidatus Methanoperedens-like archaea, is a new addition in the global CH4 cycle. This AOM process acts as a novel pathway for CH4 emission reduction in freshwater aquatic ecosystems; however, its quantitative importance and regulatory factors in riverine eco-systems are nearly unknown. Here, we examined the spatio-temporal changes of the communities of Meth-anoperedens-like archaea and nitrate-driven AOM activity in sediment of Wuxijiang River, a mountainous river in China. These archaeal community composition varied significantly among reaches (upper, middle, and lower reaches) and between seasons (winter and summer), but their mcrA gene diversity showed no significant spatial or temporal variations. The copy numbers of Methanoperedens-like archaeal mcrA genes were 1.32 x 105-2.47 x 107 copies g- 1 (dry weight), and the activity of nitrate-driven AOM was 0.25-1.73 nmol CH4 g-1 (dry weight) d-1, which could potentially reduce 10.3% of CH4 emissions from rivers. Significant spatio-temporal variations of