In marine sediments the anaerobic oxidation of methane with sulfate as electron acceptor (AOM) consumes the majority of the potential greenhouse gas methane. AOM is performed by consortia of anaerobic methane oxidizing archaea (ANME) and their specific partner bacteria. The physiology of these organisms is poorly understood. Here we analyzed the archaeal and bacterial diversity in different laboratory enrichment cultures that have been enriched with methane and sulfate as sole electron donors and acceptors. Using the phylogenetic information and experiments we assign AOM and side reactions in the culture to different organisms.