Integration of Carbon, Sulfur, and Iron Cycling in Anaerobic Methane Oxidation

Seep sediments are dominated by intensive microbial sulfate reduction coupled to the anaerobic oxidation of methane (AOM).

The Science

Researchers at the California Institute of Technology and partner institutions in the United Kingdom and Israel have uncovered new evidence of a significant role for iron minerals in accelerating the rates of AOM processes. Sediments with higher levels of iron oxides had decreased rates of methane release and increases in AOM processes. By using a series of microcosm experiments and carefully tracking conversion of isotopically labeled CH4 and SO4 in the presence of varying concentrations of the iron mineral hematite, the team determined that the presence of iron oxides stimulated bacterial sulfate reduction, facilitating recycling of reduced sulfur compounds back to SO4, and driving increased rates of methane consumption by archaea. These findings reveal new biological linkages in the biogeochemical cycling of carbon, sulfur, and iron and will have important implications in predicting the contribution of AOM processes to the global carbon cycle.


Coastal wetlands and ocean sediments are significant sites of methane (CH4) production, either through decomposition of organic material or via natural seepage from deeper geological reservoirs. These environments are home to unique microbial communities capable of converting CH4 to carbon dioxide (CO2) even in the absence of oxygen, which does not penetrate below the top few centimeters of sediment. No individual microbe or microbial species can generate enough energy to survive using this mode of metabolism. However, symbiotic partnerships between methane-consuming archaea and sulfate-reducing bacteria thrive using a collaborative metabolism called anaerobic oxidation of methane (AOM). In this mode of growth, electrons freed during CH4 oxidation by archaea are transferred to sulfate (SO4) by the bacterial partner, generating energy for both organisms. Since this process results in the conversion of up to 90% of available CH4 to CO2 (a much less potent greenhouse gas) in some environments, studying its mechanistic basis and the organisms performing it could have major implications for understanding the global carbon cycle and potential climate change impacts.

BER Program Manager

Dawn Adin

U.S. Department of Energy, Biological and Environmental Research (SC-33)
Biological Systems Science Division
[email protected]


Sivan, O., G. Antler, A. V. Turchyn, J. J. Marlow, and V. J. Orphan. 2014. “Iron Oxides Stimulate Sulfate-Driven Anaerobic Methane Oxidation in Seeps,” Proceedings of the National Academy of Sciences (USA), DOI:10.1073/pnas.1412269111.