As methane is a very stable molecule, its degradation without oxygen or sulfate is impossible, or so it was thought until 2006 when a team of researchers discovered Methylomirabilis oxyfera, an anaerobic bacterium, i.e., that can live without oxygen and can oxidize methane without using oxygen. To do so, the microorganism uses nitrites in freshwater sediments in farming areas. Now, the same research team, the outcome of a joint international undertaking involving CEA, CNRS and Evry-Val-d'Essonne University, has just proven that the same bacterium uses an entirely new enzymatic process to produce oxygen from nitrites and uses it to oxidize methane. The research that led to the discovery of the new oxygen producing pathway, which may precede the development of photosynthesis that enables the existence of an aerobic metabolism in an oxygen deprived atmosphere, has just been published in the March 25 issue of Nature.
As Methylomirabilis oxyfera grows very slowly in an anaerobic environment and within a complex microbial community, understanding the new oxygen producing pathway was not easy. The Genoscope researchers at the CEA Life Sciences Department used a global approach by sequencing the entire DNA of the community. Based on the sequencing data, they were able to reconstruct the entire genome of the bacterium. Based on their results, the researchers then demonstrated that the genes usually involved in nitrite reduction are lacking in the genome. So, they hypothesized that there was another nitrite reduction pathway in the bacterium and that it was able to produce its own oxygen and use it to oxidize methane. The researchers have now proven their hypothesis by capturing the endogenous oxygen.