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

Abstract

Arctic lakes emit methane (CH₄) to the atmosphere. The magnitude of this flux could increase with permafrost thaw but might also be mitigated by microbial 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 <i>Methylomonadaceae</i> and including the predominant genus <i>Methylobacter</i> as well as <i>Crenothrix</i>, could be the major methane-oxidizing bacteria (MOB) in the anoxic water of the four lakes. Correlation between <i>Methylomonadaceae</i> and OTUs within <i>Methylotenera</i>, <i>Geothrix</i> and <i>Geobacter</i> genera indicated that AOM might occur in an interaction between MOB, denitrifiers and iron-cycling partners. We conclude that MOB within <i>Methylomonadaceae</i> could have a crucial impact on CH₄ cycling in these Siberian Arctic lakes by mitigating the majority of produced CH₄ before it leaves the anoxic zone. This finding emphasizes the importance of AOM by <i>Methylomonadaceae</i> and extends our knowledge about CH₄ cycle in lakes, a crucial component of the global CH₄ cycle.