Microbial communities in iron-rich sediments

Methane is an important greenhouse gas on Earth and its flux from marine and terrestrial environment is largely controlled under anoxic condition via anaerobic oxidation of methane (AOM). Archaeal methanotrophs affiliating with ANME-1, -2 and -3 are responsible for AOM in marine environments whereas AAA (AOM-associated archaea) group within Methanosarcinales is known as a methane consumer in freshwater setting. Nitrate, nitrite, sulfate, Fe(III) and Mn(IV) can be used as electron acceptors of freshwater AOM. Among them, AOM coupled to iron (hydr)oxides reduction (Fe-AOM) is expected as an important process for methane removal in freshwater sediments. In this study, we explored iron-rich freshwater pond to understand methane cycle associated with the physical and chemical condition. Our results suggest that iron-dependent methane oxidation by AAA group is enhanced due to abundant supply of iron oxide in the freshwater surface sediments.