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29 March 2023
Published online 16 January 2020
Algal blooms caused by pollution runoff could contribute greater quantities of methane to the atmosphere as the planet warms.
Scientists from Germany, Jordan, the UK, Israel and Spain have found direct evidence that cyanobacteria, also called blue-green algae, produce methane, possibly through photosynthesis.
The finding contradicts the once popular notion that the only biological organisms capable of generating methane were the single-celled Archaea, and that this demanded the absence of oxygen.
Researchers, led by Mina Bizic and Hans-Peter Grossart from the Leibniz Institute of Freshwater Ecology and Inland Fisheries in Germany, cultured different strains of cyanobacteria isolated from marine, freshwater and terrestrial environments, using sodium hydrogen carbonate as a carbon source.
They measured patterns and rates of methane production using mass spectrometry. Measurements, lasting two to five days, showed continuous methane production in the absence and presence of oxygen, with rates dipping during darkness compared to when it was light.
Methane production stopped when cyanobacteria photosynthesis was blocked using specific inhibitor molecules. The finding indicates that cyanobacteria convert carbon dioxide to methane using a mechanism that might be closely linked to photosynthesis. At night, when production rates drop, the organisms are probably relying on stored compounds for this process.
“This study puts forward the option of a feedback loop where cyanobacteria emit methane and intensify global warming,” says Bizic. Global warming, in turn, could trigger explosive growth of cyanobacteria.
“The new research is provocative,” says Rick Cavicchioli, an environmental microbiologist at the University of New South Wales in Australia who was not involved in the study. But the mechanisms and environmental factors that regulate methane production by cyanobacteria at a cellular, community, ecosystem and ultimately global level still need to be clarified, he adds.
Bizic, M. et al. Aquatic and terrestrial cyanobacteria produce methane. Sci. Adv. 6, eaax5343 (2020).