Microbes that consume methane could be used to help slow global warming. Researchers have identified many methane-eating bacteria, known as methanotrophs, but in nature these organisms tend to take in only small amounts of this very potent greenhouse gas. That’s because methane is found in the atmosphere at a concentration of 1.9 parts per million (ppm), while methanotrophs typically grow best when methane levels range around 5,000 to 10,000 ppm.
Chemical engineer Mary Lidstrom of the University of Washington and her colleagues wondered whether it may be possible to deploy methanotrophs to remove substantial quantities of methane from the air at areas such as landfills, rice paddies, and oil and gas fields, where methane levels can reach 500 ppm. They began a search for bacteria that may be up to the task.
In a new study, the research team reports bacterial strains that can grow at these relatively low methane levels. More importantly, the researchers identified a strain, Methylotuvimicrobium buryatense 5GB1C, that consumed the methane at higher rates even when the gas was available at concentrations from 200 to 1,000 ppm (Proc. Natl. Acad. Sci. U.S.A. 2023, DOI: 10.1073/pnas.2310046120).
“Most people just kind of pooh-poohed this idea of using methanotrophs,” says Mary Ann Bruns, a soil microbiologist at the Pennsylvania State University who was not involved in the research. To her, the results demonstrate the potential of using these organisms for effective methane removal and investing in the search for other good microbial candidates.
For their study, Lidstrom and colleagues selected six bacteria representing diverse methanotroph groups and tested their ability to grow inside glass tubes with stoppers at a methane level of 500 ppm. While four of the six methane-eating bacteria showed growth over 14 days, M. buryatense 5GB1C grew the fastest. When the researchers further tested this methanotroph’s performance at seven methane levels ranging between 100 and 2,500 ppm, they saw growth at concentrations as low as 200 ppm.
“I was very surprised,” Lidstrom says. “This is a strain that grows extremely well at high methane, and I expected the ability to grow at low methane would be the opposite.”
Her team observed that M. buryatense 5GB1C might be successful because of its ability to conserve energy at low methane levels. “They’re able to tamp down all their metabolism, all their cellular processes,” Lidstrom says, “and grow at 4% of the rate that they do at high methane.” While growing slowly, these microbes continue to use up whatever methane is available, which means they can keep removing the gas.
Now Lidstrom’s team wants to genetically modify M. buryatense 5GB1C so it can consume methane faster at 500 ppm. The plan is to test the organism’s performance inside bioreactors, which will pull in methane-rich air. Her collaborators are currently working on a better bioreactor design for this project. With an improved strain and bioreactor design, the researchers expect that each treatment plant could remove 40 to 250 metric tons of methane every year. It might require hundreds of thousands of such plants to substantially reduce the amount of methane that enters the atmosphere.
“It’s a promising technology, but it’s not yet clear if it will be feasible,” Lidstrom says. While her team and others continue to test greenhouse gas removal strategies, decreasing emissions to combat climate change remains crucial. “The world needs both,” she adds.