Widespread formation of methane by Cyanobacteria in aquatic and terrestrial environments

Evidence is accumulating to challenge the paradigm that biogenic methanogenesis, traditionally considered a strictly anaerobic process, is exclusive to Archaea. This change in our perception on methane production has important consequences for the feedback with global climate. Our study shows that cyanobacteria produce methane at substantial rates under light and dark oxic conditions, demonstrating biogenic methane production within the Bacteria, the second prokaryotic domain. Biogenic methane production was enhanced during oxygenic photosynthesis and directly attributed to the cyanobacteria by stable isotope labelling. Global production of methane by cyanobacteria is conservatively estimated to be up to 20 Tg CH4 per year, about a third of the methane thought to be emitted from non-wetland biogenic sources. Climate change, leading to worldwide increases in cyanobacterial blooms frequency and intensity will accordingly have a direct feedback on warming. With a ubiquitous presence on Earth for 3.5 billion years, cyanobacteria have had and will continue to have a substantial, yet not considered, impact on the global methane budget.