Anaerobic oxidation of methane

Anaerobic oxidation of methane (AOM) is a methane-consuming microbial process occurring in anoxic marine and freshwater sediments.

[1] During AOM, methane is oxidized with different terminal electron acceptors such as sulfate, nitrate, nitrite and metals, either alone or in syntrophy with a partner organism.

ANME's are very closely related to methanogenic archaea and recent investigations suggest that AOM is an enzymatic reversal of methanogenesis.

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.

In 2010, omics, especially metagenomics, analysis showed that nitrite reduction can be coupled to methane oxidation by a single bacterial species Candidatus Methylomirabilis oxyfera (phylum NC10), without the need for an archaeal partner.

Three mechanisms of Anaerobic Oxidation of Methane (AOM). The first method (top) is mediated by a consortium of anaerobic methanotrophic (ANME) archaea from the clades 1,2a,2b & 2c and sulfate reducing bacteria (SRB). The oxidation of methane occurs in the ANME where electrons are passed directly to the SRB, which performs sulfate reduction [ 3 ] . [ 4 ] The second method (middle) links methane oxidation with nitrate reduction, mediated by consortia of ANME archaea and Anammox bacteria. [ 5 ] The third mechanism (bottom) also links methane oxidation with nitrate reduction but is mediated by ANME archaea and NC10 bacteria. Unlike the first two mechanisms, both the ANME archaea and NC10 bacteria compete for methane. [ 6 ]