Nitrite-driven anaerobic methane oxidation by oxygenic bacteria.

Journal: Nature
Published:
Abstract

Only three biological pathways are known to produce oxygen: photosynthesis, chlorate respiration and the detoxification of reactive oxygen species. Here we present evidence for a fourth pathway, possibly of considerable geochemical and evolutionary importance. The pathway was discovered after metagenomic sequencing of an enrichment culture that couples anaerobic oxidation of methane with the reduction of nitrite to dinitrogen. The complete genome of the dominant bacterium, named 'Candidatus Methylomirabilis oxyfera', was assembled. This apparently anaerobic, denitrifying bacterium encoded, transcribed and expressed the well-established aerobic pathway for methane oxidation, whereas it lacked known genes for dinitrogen production. Subsequent isotopic labelling indicated that 'M. oxyfera' bypassed the denitrification intermediate nitrous oxide by the conversion of two nitric oxide molecules to dinitrogen and oxygen, which was used to oxidize methane. These results extend our understanding of hydrocarbon degradation under anoxic conditions and explain the biochemical mechanism of a poorly understood freshwater methane sink. Because nitrogen oxides were already present on early Earth, our finding opens up the possibility that oxygen was available to microbial metabolism before the evolution of oxygenic photosynthesis.

Authors
Katharina Ettwig, Margaret Butler, Denis Le Paslier, Eric Pelletier, Sophie Mangenot, Marcel Kuypers, Frank Schreiber, Bas Dutilh, Johannes Zedelius, Dirk De Beer, Jolein Gloerich, Hans J C Wessels, Theo Van Alen, Francisca Luesken, Ming Wu, Katinka Van De Pas Schoonen, Huub J Op Den Camp, Eva Janssen Megens, Kees-jan Francoijs, Henk Stunnenberg, Jean Weissenbach, Mike S Jetten, Marc Strous