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Abstract

Anaerobic methanotrophic archaea of the ANME clades -1, -2, -3 are cosmopolitan and ubiquitous in all environments on Earth where sulfate and methane intersect. Closely related gene sequences of anaerobic methanotrophs are found in subsurface and surface sediments, terrestrial, and marine settings or benthic and pelagic habitats. Although their diversity is limited, various subgroups of the ANME clades co-occur in most methane habitats. Microscopic analysis as well as quantitative PCR of their distribution has revealed the dominance of certain types within microniches in the environments, indicating an effect of environmental conditions on distribution. Diverse forms of associations between the different ANME subgroups and various partner bacteria have been microscopically identified by fluorescence in situ hybridization, and ANME cells have also been detected without a bacterial partner attached. However, the most common form of occurrence of ANME in hot spots of the anaerobic oxidation of methane are small shell-type consortia with sulfate-reducing bacteria as partners.