title: Archaea catalyze iron-dependent anaerobic oxidation of methane.
abstract: Anaerobic oxidation of methane (AOM) is crucial for controlling the emission of this potent greenhouse gas to the atmosphere. Nitrite-, nitrate-, and sulfate-dependent methane oxidation is well-documented, but AOM coupled to the reduction of oxidized metals has so far been demonstrated only in environmental samples. Here, using a freshwater enrichment culture, we show that archaea of the orderMethanosarcinales, related to "CandidatusMethanoperedens nitroreducens," couple the reduction of environmentally relevant forms of Fe3+and Mn4+to the oxidation of methane. We obtained an enrichment culture of these archaea under anaerobic, nitrate-reducing conditions with a continuous supply of methane. Via batch incubations using [13C]methane, we demonstrated that soluble ferric iron (Fe3+, as Fe-citrate) and nanoparticulate forms of Fe3+and Mn4+supported methane-oxidizing activity. CO2and ferrous iron (Fe2+) were produced in stoichiometric amounts. Our study connects the previous finding of iron-dependent AOM to microorganisms detected in numerous habitats worldwide. Consequently, it enables a better understanding of the interaction between the biogeochemical cycles of iron and methane.
authors: Department of Microbiology, Institute for Water and Wetland Research, Radboud University, Heyendaalseweg 135, 6525 AJ Nijmegen, The Netherlands k.ettwig@science.ru.nl bkartal@mpi-bremen.de.
authors: Katharina F
authors: KF
authors: Ettwig
authors: Department of Microbiology, Institute for Water and Wetland Research, Radboud University, Heyendaalseweg 135, 6525 AJ Nijmegen, The Netherlands.
authors: Baoli
authors: B
authors: Zhu
authors: Department of Microbiology, Institute for Water and Wetland Research, Radboud University, Heyendaalseweg 135, 6525 AJ Nijmegen, The Netherlands.
authors: Daan
authors: D
authors: Speth
authors: Department of Microbiology, Institute for Water and Wetland Research, Radboud University, Heyendaalseweg 135, 6525 AJ Nijmegen, The Netherlands.
authors: Jan T
authors: JT
authors: Keltjens
authors: Department of Microbiology, Institute for Water and Wetland Research, Radboud University, Heyendaalseweg 135, 6525 AJ Nijmegen, The Netherlands.
authors: Mike S M
authors: MSM
authors: Jetten
authors: Department of Microbiology, Institute for Water and Wetland Research, Radboud University, Heyendaalseweg 135, 6525 AJ Nijmegen, The Netherlands k.ettwig@science.ru.nl bkartal@mpi-bremen.de.
authors: Boran
authors: B
authors: Kartal
keywords: anaerobic oxidation of methane; archaea; iron reduction; manganese reduction; multiheme proteins