Anaerobic oxidation of methane and associated microbiome in anoxic water of Northwestern Siberian lakes

Abstract

Arctic lakes emitmethane (CH4) to the atmosphere. The magnitude of this flux could increasewith permafrost thaw butmight also be mitigated bymicrobial CH4 oxidation. Methane oxidation in oxic water has been extensively studied, while the contribution of anaerobic oxidation of methane (AOM) to CH4 mitigation is not fully understood.We have investigated four Northern Siberian stratified lakes in an area of discontinuous permafrost nearby Igarka, Russia. Analyses of CH4 concentrations in the water column demonstrated that 60 to 100% of upward diffusing CH4 was oxidized in the anoxic layers of the four lakes. A combination of pmoA and mcrA gene qPCR and 16S rRNA gene metabarcoding showed that the same taxa, all within Methylomonadaceae and including the predominant genus Methylobacter aswell as Crenothrix, could be themajor methane-oxidizing bacteria (MOB) in the anoxic water of the four lakes. Correlation between Methylomonadaceae and OTUs within Methylotenera, Geothrix and Geobacter genera indicated that AOMmight occur inan interactionbetweenMOB, denitrifiers and iron-cycling partners. We conclude thatMOBwithinMethylomonadaceae could have a crucial impact on CH4 cycling in these Siberian Arctic lakes bymitigating themajority of produced CH4 before it leaves the anoxic zone. This finding emphasizes the importance of AOM by Methylomonadaceae and extends our knowledge about CH4 cycle in lakes, a crucial component of the global CH4 cycle.