Direct phylogenetic and isotopic evidence for multiple groups of archaea involved in the anaerobic oxidation of methane

The biological oxidation of methane by anaerobic microorganisms is a significant sink for methane in the marine environment. Although there is convincing biogeochemical evidence for anaerobic oxidation of methane (AOM) by methanotrophic archaea and sulfate-reducing bacteria, the identity of these uncultured microorganisms is only now being described. In this study, we examined the diversity archaeal and bacterial assemblages involved in AOM using directly coupled isotopic and phylogenetic analyses at the level of single cells. The combined application of fluorescent in situ hybridization and secondary ion mass spectrometry (FISHSIMS) identified two phylogenetically distinct groups of archaea (ANME-1 and ANME-2) from marine methane seeps that were extremely depleted in carbon-13 (-83‰) and appear to be capable of directly oxidizing methane. These archaeal groups were observed to exist as monospecies aggregates or single cells as well as in physical association with bacteria including, but not limited to, members of the sulfate-reducing Desulfosarcina. The results from this work illustrate the complexity of the microbial communities and possible mechanisms involved in AOM. FISH-SIMS is an effective approach for understanding the dynamic microbial interactions within diverse methane-associated communities and may provide a useful culture-independent tool for deciphering the metabolic function of other environmentally significant microorganisms in situ