Response of the Anaerobic Methanotrophic Archaeon "" to the Long-Term Ferrihydrite Amendment

Anaerobic methanotrophic (ANME) archaea can drive anaerobic oxidation of methane (AOM) using solid iron or manganese oxides as the electron acceptors, hypothetically direct extracellular electron transfer (EET). This study investigated the response of " TS" (type strain), an ANME archaeon previously characterized to perform nitrate-dependent AOM, to an Fe(III)-amended condition over a prolonged period. Simultaneous consumption of methane and production of dissolved Fe(II) were observed for more than 500 days in the presence of " TS," indicating that this archaeon can carry out Fe(III)-dependent AOM for a long period. " TS" possesses multiple multiheme -type cytochromes (MHCs), suggesting that it may have the capability to reduce Fe(III) EET. Intriguingly, most of these MHCs are orthologous to those identified in "," an Fe(III)-reducing ANME archaeon. In contrast, the population of " TS" declined and was eventually replaced by "," implying niche differentiation between these two ANME archaea in the environment.