THE BACTERIA THAT EAT METHANE

An Interview With Soo Ro, Molecular Biophysicist

By: Alex Berr

Methane leaking through cracks in the Arctic tundra. Photo by NASA’s Earth Observatory; used under Creative Commons.

What do cows, landfills, and petroleum extraction all have in common? Each produces methane, one of the greenhouse gases trapping heat in our atmosphere and warming the planet. This gas is potent: it has over twenty times the heat-trapping capacity of the most familiar greenhouse gas, carbon dioxide. Methane is building in the atmosphere at an increasing rate, creating a thick blanket that warms the earth.

One way to slow this warming is to destroy methane. By breaking the bonds holding it together, it won’t be able to trap heat. But methane is one of the hardest molecules to break. And while humans have no way of splintering this bond, it’s possible that other lifeforms do.

Deep in the oceans and in the crawl spaces of swamps live a type of bacteria that hold the key to dismantling methane gas. These bacteria are called methanotrophs, a name that literally means “fueled by methane.” Methanotrophs survive extreme conditions by eating methane. They house a unique protein called methane monooxygenase, or MMO. MMO is an enzyme that contains a powerful weapon: metal. The copper metal in MMO uses stored energy to destroy the super-strong methane bond and make MMO the only known protein on Earth that can break apart methane.

Soo Ro, a graduate student at Northwestern University, is working to understand how MMOs break down methane naturally. Ro is a member of Dr. Amy Rosenzweig’s lab, which studies how MMOs use copper to break apart the bonds in methane.

Ro is studying how a specific type of MMO, particulate MMO (pMMO), breaks down methane in its outer edges. To do this, first Ro and other members of her lab must grow methanotrophs— the bacteria that naturally contain MMO. She starts this process by feeding the methanotrophs 12 liters of sugary red liquid; this encourages the bacteria to divide exponentially. The methanotrophs grow in a metal bioreactor that spans from the lab bench to the ceiling. Over the course of a week, the liquid inside the bioreactor bubbles and turns from red to yellow. At the end of the week, Ro collects about 100 grams of bacteria— the bacterial weight of a small lemon.

But the methanotrophs are finicky; sometimes they don’t grow, and Ro must start the whole process over. Once Ro has enough bacteria to conduct her experiments, she must work quickly, or the proteins she is extracting will fall out of solution and lose their biological function.

While working against the clock, Ro must also take critical precautions: working with methane can be quite dangerous. Methanotrophs require methane to survive, so Ro’s giant bioreactor is full of it. Methane is a colorless, odorless gas that could cause a massive fire if it leaks. Ro and her labmates must take extra safety measures when using methane, like checking gas lines for clogs and applying soap to each junction that will gurgle and froth if the explosive gas begins to escape.

Despite its challenges, this laborious process is worth it to Ro. She is hopeful that her research will lead to sustainable ways to clear greenhouse gases from the atmosphere. “Methane emissions are only going to continue to rise,” Ro explains. “By understanding how the protein, pMMO, uses copper to break methane, chemists can create synthetic catalysts that can mimic the chemistry for methane remediation purposes.” And that’s not all. She adds, “On the biotechnology side, we can engineer methanotrophs to eat methane and convert that into biofuels, so that energy isn’t wasted into the air.”

Ro notes that at this point, “The field still has limited understanding of methanotrophic bacteria…The more we get to understand methanotrophs, the easier it will be to perform biochemical analysis and create biotechnology platforms.” Ro expects the field is still at least a decade from understanding how methanotrophs work, yet she is hopeful for what’s to come. She believes that her fundamental biological studies will someday have a tangible impact on global warming.