Methane (CH4) is an important greenhouse gas. Its production (methanogenesis) occurs mainly by microorganisms in anaerobic environments, and the oxidation of methane (methanotrophy) is also a microbial process. Methanotrophy was shown to occur mainly in aerobic freshwater environments, while in marine sediments the anaerobic oxidation of methane (AOM) via sulfate by a consortium of bacteria and archaea is the main mechanism.
In this study we use pyrosequencing to investigate the changes in the microbial communities with sediment depth related to the change in dominant electron acceptors. A novel process of iron oxide reduction coupled to AOM in the sediments of Lake Kinneret (LK) is shown from geochemical and microbial evidences.
The results of nitrate, sulfate, ferrous and methane concentrations in in-situ porewater profiles show a change in the electron acceptors. Methane profiles indicate a sink for methane below the depths at which nitrate and sulfate are completely exhausted and also below the zone of methanogenesis.
Based on these results functional genes and 16S rRNA gene analysis of the communities` structure and diversity of bacteria and archaea along three different sediment depths were carried out. The discovered microbial communities show a shift with depth along with various electron acceptors. Variations in microbial communities could help indicate which microorganisms perform the dominate processes at different depths. This evidence of the microbial communities could further support the hypothesis of iron dependent AOM in LK sediments.
