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Because of its potent greenhouse properties, methane gas is a significant contributor to climate change. It also feeds microbes known as methanotrophs that convert the gas into carbon dioxide and biomass, but scientists have been unsure how these microbes get all the nutrients they need to accomplish this task.

Now, a University of Utah chemistry lab has developed a novel technique for studying these microbial communities and has used it to discover a new molecule that enables methane-oxidizing bacteria to acquire iron from the environment, which is important for understanding how these organisms sequester methane, keeping it out of the atmosphere.

The findings, in Proceedings of the National Academy of Sciences, also provide information that could be useful for harnessing methanotrophs to convert methane into useful chemicals and liquid fuels, according to principal investigator Aaron Puri, an assistant professor of chemistry and member of the U's Henry Eyring Center for Cell & Genome Science.

"Understanding these types of mechanisms that they use to interact with their environment is critical if we're going to optimize using them for useful tasks," Puri said. "We've also identified a key link between how iron exists on Earth and how gases are cycled in the atmosphere, which is through these methane-oxidizing bacteria, and more specifically through this new molecule that we've discovered."

Methane, or CH_4, the simplest hydrocarbon molecule, is the main ingredient of natural gas that fuels home appliances. This gas is also released from decomposing organic matter, commonly at landfills or swamps. It packs about 80 times more heat-trapping power in the short term than carbon dioxide, a longer-lived gas that is the main driver of anthropogenic climate change.

Microbes naturally break down CH₄ through an oxidation process that yields carbon dioxide and organic compounds.

Puri's study introduces a new tool called "inverse stable isotope probing–metabolomics," or InverSIP, which links genes found in microbial DNA with the actual small molecules called metabolites those genes produce. Using this method, the Puri Lab discovered a previously unknown iron-grabbing molecule made by methane-eating bacteria. They dubbed the molecule methylocystabactin.

It functions like a claw that pulls iron from the environment and makes it available for enzymes that oxidize methane. But it gets even more interesting.

"We identified other bacteria that exist in the same community that don't make this molecule, but can basically hijack the molecule that's made by other members for their own benefit," Puri said. "In some systems we'll call those 'cheaters' because they're benefiting without using their energy to make the molecule."

Overall, this discovery explains a crucial part of how methane-consuming microbes survive and shows how InverSIP can unlock hidden molecular details in other microbial communities important for climate, ecosystems and health.

"What it's showing us is the importance of this iron-binding molecule for these microbial communities," Puri said. "What we're really excited about with this approach is that we can also apply it more generally to other microbial communities to figure out these molecular details of how they're interacting. We could imagine applying this to a human-associated microbiome or other environmental microbiomes that are interesting."