Raghoebarsing, A.A., Pol, A., Van de Pas-Schoonen, K.T., Smolders, A.J., Ettwig, K.F., Rijpstra, W.I.C., Schouten, S., DamstÃ©, J.S.S., den Camp, H.J.O., Jetten, M.S. and Strous, M., 2006. A microbial consortium couples anaerobic methane oxidation to denitrification. Nature, 440(7086), p.918.
Modern agriculture has accelerated biological methane and nitrogen cycling on a global scale1,2. Freshwater sediments often receive increased downward fluxes of nitrate from agricultural runoff and upward fluxes of methane generated by anaerobic decomposition3 . In theory, prokaryotes should be capable of using nitrate to oxidize methane anaerobically, but such organisms have neither been observed in nature nor isolated in the laboratory4—8. Microbial oxidation of methane is thus believed to proceed only with oxygen or sulphate9,10. Here we show that the direct, anaerobic oxidation of methane coupled to denitrification of nitrate is possible. A microbial consortium, enriched from anoxic sediments, oxidized methane to carbon dioxide coupled to denitrification in the complete absence of oxygen. This consortium consisted of two microorganisms, a bacterium representing a phylum without any cultured species and an archaeon distantly related to marine methanotrophic Archaea. The detection of relatives of these prokaryotes in different freshwater ecosystems worldwide11—14 indicates that the reaction presented here may make a substantial contribution to biological methane and nitrogen cycles.
Methane and nitrous oxide (N2O) are both meaningful greenhouse gasses and are released by thawing permafrost as is observed in the Arctic in the past five to ten years. This paper outlines a newly-discovered consortium of microorganisms which feeds on methane and is capable of fully denitrifying nitrate to dinitrogen. If this consortium is as prevalent as the authors suggest, then it may be a critical component of remediation in rivers heavily affected by heavy agricultural runoff and melting permafrost deposits.