Margaret Butler of University of Queensland and her colleagues have identified an unusual mechanism of oxygen synthesis. It’s produced by the nonphotosynthetic bacteria Candidatus Methylomirabilis oxyfera.
M. oxyfera, a member of a group of anaerobic bacteria called NC10 first found in caves in Australia, was isolated from some ditches in the Netherlands. The bacteria were believed to be capable of converting methane to carbon dioxide, and the researchers wanted to test this. They placed the bacteria into a chamber that would allow them to carefully measure any oxygen or nitrogen either entering or leaving the chamber.
The bacteria were metabolizing methane, but that's not all. To their surprise, the scientists found that oxygen was being produced by a hitherto unknown mechanism. There is no known enzyme that will convert nitric oxide to oxygen and nitrogen gas, yet these bacteria have apparently invented such an enzyme.
Because these bacteria may predate photosynthetic bacteria on the early Earth, they could have been major contributors to oxygenating the atmosphere. In that case, aerobic organisms that utilize oxygen may have arisen before photosynthetic organisms.
One caveat is that the researchers were unable to grow pure cultures of M. oxyfera. Instead, they grew mixes of bacteria and then used DNA sequencing to reconstruct the M. oxyfera genome as well as to pick out some likely candidates for the oxygen-producing enzyme. In other words, the scientists haven’t proved that it is M. oxyfera making the oxygen. I’m sure that’s next.