Microbial interactions between iron reducing and methane oxidizing bacteria in methanogenic sediments of freshwater lake

Microbial methane oxidation in freshwater sediments can substantially reduce methane emissions to the atmosphere, yet the processes regulating this activity in the methanogenic zone have remained poorly constrained. In iron-rich sediments, methane cycling may overlap with microbial iron reduction, suggesting potential coupling between these processes. Lake Kinneret sediments exhibit such conditions at depth, where methanogenesis dominates in the presence of high concentrations of reactive iron and limited availability of alternative electron acceptors. Previous studies from Lake Kinneret methanogenic sediments pointed to the coupling between methane oxidation and iron reduction, as well as to the unexpected presence of aerobic methane-oxidizing bacteria within; however, the microbial interactions are not clear.

Here we explored whether interactions between methane-oxidizing and iron-reducing bacteria can stimulate iron reduction under the methanogenic conditions. Controlled laboratory experiments were conducted using an aerobic methane-oxidizing bacterium and an anaerobic iron-reducing bacterium incubated with porewater from the methanogenic sediment zone of Lake Kinneret, amended with ¹³C-labeled methane and amorphous ferric iron, under 1% O₂ conditions. Our findings demonstrate that methane-oxidizing bacteria are linked to microbial iron reduction through indirect interactions, likely mediated by soluble metabolites or electron-shuttling compounds. The results highlight the role of microbial interactions in regulating sedimentary redox processes and methane cycling under low-oxygen conditions.