Methanotrophic Flexibility of 'Ca. Methanoperedens' and Its Interactions With Sulphate-Reducing Bacteria in the Sediment of Meromictic Lake Cadagno

Abstract

The greenhouse gas methane is an important contributor to global warming, with freshwater sediments representing importantpotential methane sources. Anaerobic methane-oxidising archaea mitigate methane release into the atmosphere by couplingthe oxidation of methane to the reduction of extracellular electron acceptors or through interspecies electron transfer with mi-crobial partners. Understanding their metabolic flexibility and microbial interactions is crucial to assess their role in globalmethane cycling. Here, we investigated anoxic sediments of the meromictic freshwater Lake Cadagno (Switzerland), where‘Ca. Methanoperedens’ co-occur with a specific sulphate-reducing bacterium, with metagenomics and long-term incubations.Incubations were performed with different electron acceptors, revealing that manganese oxides supported highest CH4 oxida-tion potential but enriched for ‘Ca. Methanoperedens’ phylotypes that were hardly present in the inoculum. Combining datafrom the inoculum and incubations, we obtained five ‘Ca. Methanoperedens’ genomes, each harbouring different extracellularelectron transfer pathways. In a reconstructed Desulfobacterota QYQD01 genome, we observed large multi-heme cytochromes,type IV pili, and a putative loss of hydrogenases, suggesting facultative syntrophic interactions with ‘Ca. Methanoperedens’. Thisresearch deepens our understanding of the metabolic flexibility and potential interspecific interactions of ‘Ca. Methanoperedens’in freshwater lakes.