Metagenomic insights into diversity and functions of the microbial community performing iron-coupled anaerobic oxidation of methane in lake sediments

Methane (CH₄) is a significant effective greenhouse gas, whose one of its main sources is biogenic methanogenesis, which occurs in the deep anoxic sediments of aquatic environments. Microbial anaerobic oxidation of methane (AOM) regulates the release of this methane to the atmosphere through natural methane scavengers that are found near its production zone. In fresh water environment where sulfate concentration is low, metals, such as iron and manganese, can become main electron acceptors. The coupling of AOM to iron reduction has been suggested or demonstrated in a variety of marine and freshwater ecosystems, however the investigation of the microbial players and involved mechanisms is still preliminary.

Here we present a deep metagenomic survey conducted on five incubation slurry samples from the deep methanic zone of Lake Kinneret (Israel) that showed evidence for iron-coupled AOM. We generated first a general description of the ecosystem in the lake deep sediments. This general description includes a description of the overall taxonomy, its metabolic potential and a specific focus on functions related to iron reduction and methane metabolism. Based on these analyses in combination with our former geochemical insights on this process, we suggest several potential mechanisms for the process of Fe-AOM in LK deep methanic zone.