Abstract
Evidence is accumulating to challenge the paradigm that biogenic methanogenesis, traditionally considered a strictly anaerobic process, is exclusive to Archaea. Cyanobacteria are here shown to 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. Methanogenesis by Cyanobacteria partly explains the paradox of methane production in oxygen-saturated waters. Climate change, leading to worldwide increases in cyanobacterial blooms 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 impact on the global methane budget.
