Immunological localization of coenzyme M reductase in anaerobic methane-oxidizing archaea of ANME 1 and ANME 2 type

The Black Sea is a large, euxinic marine basin, in which the anaerobic oxidation of methane (AOM) plays an important role in the carbon cycle. Methane-related carbonate build-ups, found on the NW' Black Sea shelf are part of an unique microbial ecosystem. Two archaeal guilds are mainly responsible for the AOM: ANME-1 (anaerobic-methane-oxidizing communities)/DSS consortia and ANME-2/greigite-bearing DSS-consortia. These microorganisms constitute a significant sink of methane on earth, but despite their relevance for the global carbon cycle little is known about the biology of AOM. Phylogenetic and biochemical analyses suggested that ANME-archaea have supposedly reversed the methanogenic pathway. Here, we were able to localize methyl-coenzyme M reductase (MCR), which catalyzes the final step of the methane formation, in ultrathin sections. The result was obtained by the immunogold labeling technique using a specific antiserum against the MCR. This technique revealed that the MCR is located in both ANME-1- and ANME-2-archaea. The data also show that MCR-like enzymes are not only encoded in the genomes of ANME-1 and ANME-2, but are, in fact, expressed as cellular proteins at high levels.