The overall reaction is: :CH4 + SO42− → HCO3− + HS− + H2O Sulfate-driven AOM is mediated by a syntrophic consortium of methanotrophic
archaea and
sulfate-reducing bacteria. They often form small aggregates or sometimes voluminous mats. The archaeal partner is abbreviated ANME, which stands for "anaerobic
methanotroph". ANME's are very closely related to methanogenic archaea and recent investigations suggest that AOM is an enzymatic reversal of
methanogenesis. It is still poorly understood how the
syntrophic partners interact and which intermediates are exchanged between the archaeal and bacterial cell. The research on AOM is hindered by the fact that the responsible organisms have not been isolated. This is because these organisms show very slow growth rates with a minimum doubling time of a few months. Countless isolation efforts have not been able to isolate one of the anaerobic methanotrophs, a possible explanation can be that the ANME archaea and the SRB have an obligate syntrophic interaction and can therefore not be isolated individually. In
benthic marine areas with strong methane releases from fossil reservoirs (e.g. at
cold seeps,
mud volcanoes or
gas hydrate deposits) AOM can be so high that
chemosynthetic organisms like filamentous sulfur bacteria (see
Beggiatoa) or animals (clams, tube worms) with
symbiont sulfide-oxidizing bacteria can thrive on the large amounts of
hydrogen sulfide that are produced during AOM. The
bicarbonate (HCO3−) produced from AOM can (i) get sequestered in the sediments by the precipitation of
calcium carbonate or so-called methane-derived
authigenic carbonates and (ii) get released to the overlying water column. Methane-derived
authigenic carbonates are known to be the most 13C depleted carbonates on Earth, with δ13C values as low as -125 per mil
PDB reported. ==Coupled to nitrate and nitrite reduction==