Archaea are a major branch of life, but we still have a lot to learn about these microbes, which were only discovered in the 1970s. They are now known to play a variety of roles in environmental cycles like nutrient fluxes. Scientists have now identified three archaeal microbes that produce methane. It was once thought that only eukaryotic cells produced methane, but these reports have provided evidence that some archaea can generate methane too. Methane is a potent greenhouse gas and is a major contributor to climate change. Researchers have been trying to identify and understand the sources and cycles of methane in the atmosphere for many years.
Two of these single-celled methane producers, or methanogens, were found in the extreme environments of Yellowstone's hot springs. The third was isolated from samples taken from an oil field. These findings were reported in three separate studies, all in Nature.
It was only about a decade ago that researchers identified the first microbial genes that would lead to the production of methane. They were found in archaeal cells in the Thermoproteota phylum, in the groups Methanomethylicia and Methanodesulfokora.
"All we knew about these organisms was their DNA. No one had ever seen a cell of these supposed methanogens; no one knew if they actually used their methanogenesis genes or if they were growing by some other means," said the senior author of two of the studies, Roland Hatzenpichler, an associate professor at MSU, among other appointments.
The Hatzenpichler lab wanted to determine if these microbes were using methanogenesis to survive. Archaea have been very challenging to study in the lab because they are so difficult to sustain and grow. The microbes that the lab focused on in this study came from hot springs that are normally 61 to 72 degrees Celsius (141 to 161 degrees Fahrenheit). But the researchers were able to surmount that hurdle, and grow the archaea in the lab. They showed that the archaea were indeed producing methane. They also learned more about the microbes with additional experiments.
Another group of researchers also succeeded in growing archaea in the lab and showing that they were methanogens.
Although Methanodesulfokora probably lives exclusively in hot springs and hydrothermal vents deep in the ocean, Methanomethylicia are more widespread, and might be found in places like soil, wetlands, and wastewater treatment plants, as well as cow digestive tracts, noted Hatzenpichler.
Methanogens are thought to be responsible for the production of about 70 percent of the methane in the atmosphere. This methane will have an environmental cost.
"Methane levels are increasing at a much higher rate than carbon dioxide, and humans are pumping methane at a higher rate into the atmosphere than ever before," Hatzenpichler said.
Scientists still have more to learn about methanogens, such as how often they pump out methane, or whether they have and use alternative survival strategies. The researchers are planning to learn more about how these microbes behave in nature, and whether they are producing methane in soil, wetlands, or other places.
You can check out an infographic relating to methane and the environment here.
Sources: Montana State University (MSU), Kohtz et al Nature 2024, Krukenberg et al Nature 2024, Wu et al Nature 2024
