Reference Work Entry

Handbook of Hydrocarbon and Lipid Microbiology

pp 887-907

The Biochemistry of Anaerobic Methane Oxidation

  • M. TauppAffiliated withDepartment of Microbiology and Immunology, Life Sciences Centre, University of British Columbia
  • , L. ConstanAffiliated withDepartment of Microbiology and Immunology, Life Sciences Centre, University of British Columbia
  • , S. J. HallamAffiliated withDepartment of Microbiology and Immunology, Life Sciences Centre, University of British Columbia

Abstract:

The anaerobic oxidation of methane (AOM) is a globally significant biogeochemical process that exerts a profound influence on methane flux between oceanic and atmospheric compartments of the biosphere. In marine sediments AOM occurs in a region of sulfate and methane depletion known as the sulfate–methane transition zone (SMTZ) where methane is converted to carbon dioxide and reduced products that are in turn used as electron donors in the conversion of sulfate to hydrogen sulfide and water. From a bioenergetic perspective, AOM represents a major source of maintenance energy within the SMTZ, and despite low estimated free energy yields supports a vigorous microbial metabolism. Lipid biomarker, phylogenetic stain and environmental PCR studies aimed at determining the biological component of AOM converge on microbial communities dominated by uncultivated anaerobic methane-oxidizing archaea (ANME-1, ANME-2 and ANME-3) and sulfate reducing bacteria (SRB). Specific physical associations between these groups have been observed consistent with syntrophic modes of growth. However, despite extensive mesocosm and labeling studies the precise mode of electron transfer between ANME and SRB remains unknown. Recent cultivation-independent studies of AOM communities from the Eel River Basin, Hydrate Ridge and the Black Sea have led to preliminary reconstruction of the genes and pathways mediating carbon and energy metabolism within ANME subgroups providing a genomic and proteomic basis for inferring substrate ranges, intermediates and terminal electron acceptors. The following chapter reviews biochemical aspects of AOM with special emphasis on pathway validation, electron flow and enzyme function. We consider how ANME subgroup partitioning and gene expression profiles overlap with prevailing thermodynamic models and speculate on syntrophic growth models as they relate to broader aspects of community metabolism within AOM sediments.