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Cyanobacteria produce methane


Cyanobacteria, also known as blue-green algae, are among the most common organisms on Earth and are notorious for forming toxins. A recent study has now shown for the first time that these bacteria produce relevant amounts of methane in oceans, inland waters, and on land.

In the course of climate change, increasing blue-green algae blooms will most likely amplify the release of methane into the atmosphere, according to scientists from the Leibniz Institute of Freshwater Ecology and Inland Fisheries (IGB) and Heidelberg University of Heidelberg who carried out the research.

Until now, methane generation by living organisms without a cell nucleus has been verified only for so-called primordial bacteria, i.e. archaea, whereby - according to the assumption - methane can only be produced under strictly anoxic conditions. The results of the study refute these assumptions.

The research team investigated 17 cyanobacterial species that occur in the sea, freshwater and soil. According to Dr Mina Bizic, a researcher at the IGB and primary author of the study, cyanobacteria in surface water are a previously unknown source of methane. As the researchers discovered, these bacteria produce the greenhouse gas during normal cellular metabolism.

To prove that methane arises in the cell, Heidelberg geoscientist Thomas Klintzsch conducted studies using isotopically labelled carbon. As part of his doctoral thesis, he was able to demonstrate how the labelled carbon is initially transferred into the biomass of the cell through photosynthesis and is then converted to methane. In laboratory experiments, the team compared the amount of methane produced by cyanobacteria with the amounts produced by archaea and organisms with cell nuclei, so-called eukaryotes. "At the same biomass, cyanobacteria produce less methane than archaea, but more methane than fungi or plants.

It is difficult to estimate the global amount of methane produced by cyanobacteria because detailed data on the biomass of these organisms in water and soil is lacking," says co-author Prof. Dr Frank Keppler, who directs the Biogeochemistry Research Group at the Institute of Earth Sciences of Heidelberg University.

It may be that cyanobacteria have been producing the greenhouse gas methane since the early days of Earth. Stromatolites, the oldest known fossils, are deposits of cyanobacteria and were found in 3.5 billion-year-old rocks in Western Australia. Cyanobacteria could therefore have influenced the Earth's climate back then. Today these bacteria are widespread throughout the world. They develop particularly well in seawater or fresh water at warm temperatures.

As a result of climate change, mass developments, so-called blue-green algae blooms, will occur more frequently and to a greater extent in the future, according to the researchers. Based on the current findings, this will also increase the emission of the greenhouse gas methane from various aquatic systems, which in turn intensifies global climate change via a positive feedback mechanism, states Prof. Dr Hans-Peter Grossart, director of the study and IGB researcher.

Besides researchers from Heidelberg University and the Leibniz Institute of Freshwater Ecology and Inland Fisheries, scientists from Greifswald, as well as Great Britain, Israel, Jordan, and Spain also contributed to the study. Their research results were published in the journal "Science Advances".

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Source: University of Heidelberg