Comparative analysis of methane-oxidizing archaea and sulfate-reducing bacteria in anoxic marine sediments

The oxidation of methane in anoxic marine sediments is thought to be mediat ed by a consortium of methane-consuming archaea and sulfate-reducing bacter ia. In this study, we compared results of rRNA gene (rDNA) surveys and lipi d analyses of archaea and bacteria associated with methane seep sediments f rom several different sites on the Californian continental margin. Two dist inct archaeal lineages (ANME-1 and ANME-2), peripherally related to the ord er Methanosarcinales, were consistently associated with methane seep marine sediments. The same sediments contained abundant C-13-depleted archaeal li pids, indicating that one or both of these archaeal groups are members of a naerobic methane-oxidizing consortia. C-13-depleted lipids and the signatur e 16S rDNAs for these archaeal groups were absent in nearby control sedimen ts. Concurrent surveys of bacterial rDNAs revealed a predominance of delta -proteobacteria, in particular, close relatives of Desulfosarcina variabili s. Biomarker analyses of the same sediments showed bacterial fatty acids wi th strong C-13 depletion that are likely products of these sulfate-reducing bacteria. Consistent with these observations, whole cell fluorescent in si tu hybridization revealed aggregations of ANME-2 archaea and sulfate-reduci ng Desulfosarcina and Desulfococcus species. Additionally, the presence of abundant UC-depleted ether lipids, presumed to be of bacterial origin but u nrelated to ether lipids of members of the order Desulfosarcinales, suggest s the participation of additional bacterial groups in the methane-oxidizing process. Although the Desulfosarcinales and ANME-2 consortia appear to par ticipate in the anaerobic oxidation of methane in marine sediments, our dat a suggest that other bacteria and archaea are also involved in methane oxid ation in these environments.