One of Earth's most prolific microorganisms is found to emit methane in amounts that could be relevant to greenhouse gas emission models, new research suggests.
Found in oceans, inland waters, and on land, Cyanobacteria, or blue-green algae, is one of the most common organisms on Earth. As human development expands and temperatures rise, the frequency and extent of algal blooms are increasing across the planet, further amplifying the release of methane into the atmosphere. Methane is the second-most important human-produced greenhouse gas after carbon and is estimated to have up to a 34 times higher warming effect over a 100-year period, the researchers note in Science Advances.
"Cyanobacteria in surface water are a previously unknown source of methane and we were able to show for the first time that these bacteria produce the greenhouse gas methane during photosynthesis," said Dr Mina Bižić, from the Leibniz-Institute of Freshwater Ecology and Inland Fisheries (IGB), in a statement.
To come to their conclusions, researchers at IGB and Heidelberg University investigated 17 species of cyanobacteria that occur in the ocean, freshwater, and soil to see how methane is formed in the cell when light energy is converted to chemical energy. They then compared the amount of methane produced by cyanobacteria with that produced by methanogenic archaea and organisms with cell nuclei, or eukaryotes.
"Cyanobacteria produce less methane than archaea, but more methane than eukaryotes. It is difficult to estimate the global amount of methane produced by Cyanobacteria because there is a severe lack of detailed data on the biomass of these organisms in water and soil," said co-author Frank Keppler, professor at the Institute of Earth Sciences at Heidelberg University.
Until now, it was believed that the only microorganisms to generate methane were archaea, single-celled microorganisms that lack a cell nuclei known as a prokaryote, under strictly anoxic conditions whereby a total depletion of oxygen has occurred. The new findings challenge that theory, suggesting that cyanobacteria may have been producing methane for billions of years. The newly identified source contributes to the natural methane budget and has likely been producing methane since cyanobacteria first evolved on Earth.
"According to our current findings, this will also increase the emission of the greenhouse gas methane from various aquatic systems, which forms an important positive feedback mechanism for [the] global climate," said senior author Professor Hans-Peter Grossart, a researcher at IGB.
Though algal blooms are a naturally occurring phenomenon, climate change is making their occurrences more intense and frequent, which may have detrimental effects on ecosystems and wildlife and can be fatal when ingested by humans.