The possible occurrence of iron-dependent anaerobic methane oxidation in an Archean Ocean analogue

Altres ajuts: Fonds pour la Formation à la Recherche dans l'Industrie et dans l'Agriculture ; Fonds De La Recherche Scientifique - FNRS, X.3007.17 In the ferruginous and anoxic early Earth oceans, photoferrotrophy drove most of the biological production before the advent of oxygenic photosynthesis, but its association with ferric iron (Fe 3+) dependent anaerobic methane (CH) oxidation (AOM) has been poorly investigated. We studied AOM in Kabuno Bay, a modern analogue to the Archean Ocean (anoxic bottom waters and dissolved Fe concentrations > 600 µmol L −1). Aerobic and anaerobic CH oxidation rates up to 0.12 ± 0.03 and 51 ± 1 µmol L −1 d −1, respectively, were put in evidence. In the Fe oxidation-reduction zone, we observed high concentration of Bacteriochlorophyll e (biomarker of the anoxygenic photoautotrophs), which co-occurred with the maximum CH oxidation peaks, and a high abundance of Candidatus Methanoperedens, which can couple AOM to Fe 3+ reduction. In addition, comparison of measured CH oxidation rates with electron acceptor fluxes suggest that AOM could mainly rely on Fe 3+ produced by photoferrotrophs. Further experiments specifically targeted to investigate the interactions between photoferrotrophs and AOM would be of considerable interest. Indeed, ferric Fe 3+ -driven AOM has been poorly envisaged as a possible metabolic process in the Archean ocean, but this can potentially change the conceptualization and modelling of metabolic and geochemical processes controlling climate conditions in the Early Earth.