How microbes can combat climate change

While carbon dioxide gets much of the focus in the climate debate, methane, the main flammable component of natural gas, also drives planetary warming. Molecule for molecule, CH₄'s heat-trapping potential is 34 times greater than that of CO₂ (on a 100-year time scale) and it's pouring into the atmosphere from both human and natural sources, posing a significant threat to global climate systems.

Now scientists from around the world are exploring various strategies for removing methane from the atmosphere in the hopes of slowing climate change.

University of Utah chemist Jessica Swanson has retooled her lab to help develop a process that would harness methane-eating bacteria, known as methanotrophs, which naturally break down methane into carbon dioxide and organic compounds. She aims to discover ways to enable methanotrophs to effectively pull methane from the air at low concentrations in next-generation bioreactors.

"I'm hopeful that the more we understand methanotrophs, the more we can also facilitate open-system, nature-based solutions," Swanson said.

Methane accounts for at least 25% of planetary warming, according to the Environmental Defense Fund. The gas is naturally oxidized in the atmosphere resulting in a shorter half-life than CO₂, but methane sources are surpassing the oxidizing capacity of the atmosphere at a shocking rate—partially due to a positive feedback cycle between warming and natural emissions from wetlands and permafrost. The consequence is rapidly increasing atmospheric methane concentrations that pose a serious risk of near-term warming.

The U's inaugural Wilkes Prize went to Lumen Bioscience this fall for its development of a virus-based product that substantially reduces the methane that forms in the gut of ruminating cattle, seen as a leading source of anthropogenic methane in the atmosphere. While Lumen's technology prevents the release of methane, Swanson and her group are looking to biotech to break down methane after it's already released into the atmosphere from belching cows and other sources.

Enter Methylotuvimicrobium buryatense 5GB1C, a strain of bacteria that eats methane out of the air at fairly low concentrations.

Featuring top experts from the University of Washington and Northwestern University, Swanson's team has secured three years of funding to support their methanotroph research from the Carbon Technology Research Foundation. They hope to develop technologies that could be deployed at methane-spewing sites, such as coal mines, oil and gas fields and landfills, where methane concentrations can be as high as 500 parts per million, or ppm.

Ambient levels of methane are about 2 ppm in the atmosphere, well below the 5,000 to 10,000 ppm most methanotrophs need to grow naturally, according to Washington's Mary Lidstrom, professor emerita of chemical engineering and a leading methanotroph researcher.

"In nature, there are bacteria that already remove methane but this happens slowly," she said. "We aim to capitalize on these common biological processes, meaning that as scientists we don't need to start from scratch."

Lidstrom recently discovered that M. buryatense can consume methane at concentrations as low as 200 to 1,000 ppm, converting much of the greenhouse gas into biomass.

"Half of that is protein and it is a source of sustainable protein. You get about 0.8 tons of biomass per ton of methane and there's an estimated value of about $1,600 a ton for fish food," Lidstrom said at a recent methane removal workshop hosted by the National Academy of Sciences.

Swanson's other collaborator is Northwestern's Amy Rosenzweig, who has also made key discoveries into how these microbes oxidize methane.

The Swanson lab has long explored molecular biophysics using multiscale simulations. She now is focusing this expertise on characterizing each stage of methane uptake, delivery and oxidation. These insights would guide bioengineering approaches to enhance the efficiency of methanotrophs in breaking down methane.

The team plans to genetically modify M. buryatense so that it consumes methane faster at lower concentrations and develop methanotroph-powered thin-film bioreactors, or industrial reaction chambers, that could be deployed by the thousands in places where methane is released. Each reactor could pull up to 280 metric tons of methane out of the atmosphere a year.

If widespread deployment were accomplished, a realistic goal would be to use methanotrophs to break down 300 million tons of methane in 20 years, enough to dampen global warming by .1 to .2 degrees Celsius.

"We need dedicated funding and funding that encourages collaboration with clear targets," Swanson said. "We also need commercial investment. We can start developing these things right now for 500 ppm and we should be—getting the technology developed so we can drop in biological advances to target lower concentrations."

This project does not carry the risks of other biologically-based methane-reduction proposals, which can release nitrous oxide, a greenhouse gas far more potent than methane.

Swanson believes it's possible to develop a system that can work at 2 ppm, or ambient levels of methane. To achieve that would require a 50-fold increase in the efficiency of available technology, she said at the recent workshop.

"Two factors are going to contribute to increased efficiency: bioengineering and next-generation bioreactors," she said. "If we assign only a third (five-fold increase) to the bioreactor, we need a 10-fold increase from the biology."

Swanson believes the secret lies in the way the methanotrophic organisms are structured.

"They are jam-packed full of membranes. The stacked disks filling the cell are unusual for bacteria," she said. "A key question is can we just engineer the proteins that are naturally excreted? Can we improve the biofilms? Can we improve the outer membrane? Each of these areas has potential for improvement through bioengineering. Once answered each of these questions points, either directly or with some amount of creativity, to ways that we can improve methanotrophic efficiency."

To hear more from Jessica Swanson, listen to her interview on the Wilkes Center's Talking Climate podcast here.

Provided by University of Utah