Fifty miles off the Tuscan coast, in a sparkling blue expanse broken only by rocky, forbidding islets, including the real-life Island of Montecristo, ancient creatures are roosting beneath the waves.

They spend their days feasting on an unlikely source of nourishment: methane, a potent greenhouse gas that leaks out of cracks in the seafloor.

Lately, researchers have been trying to put these microorganisms to work on an urgent task. If their appetites can be redirected to other sources of their favorite gas — namely, the hundreds of millions of tons of planet-warming methane emitted each year from oil and gas sites, livestock and wetlands — then they might just help slow climate change.

First, though, researchers need to better understand these microbes, which have been on this planet for billions of years but remain enigmatic in many ways.

One place they like to live is the bottom of the ocean, where methane buried inside the Earth seeps up through fissures in the seabed. In 2017, workers on fishing boats reported seeing a 30-foot jet of dirty water erupt out of the sea near Montecristo. Geologists discovered a string of offshore mud volcanoes, bubbling methane into the cerulean sea.

But nobody had tried to capture the organisms that eat the gas there until this year, when Braden Tierney and two colleagues sailed into the Tyrrhenian Sea, off the western coast of Italy, on a cool summer night.

“It is an odd feeling, floating on top of a place that violently exploded less than 10 years ago,” said Dr. Tierney, an American microbiologist, as the team’s boat bobbed in the predawn darkness.

Life in Unlivable Places

Most of the methane in Earth’s atmosphere is produced by microbes that break down plant and animal matter in bogs, landfills and the stomachs of cows. But microbes of a different type scarf down methane. And only in recent decades have scientists started to understand how they do it.

As molecules go, methane is an odd choice for any organism to eat. It’s the main ingredient in natural gas, so there’s plenty of energy in it, as anyone who has put a match to a gas pipe can tell you. But to make use of it, microbes need to perform some challenging chemical maneuvers and expend a lot of their own energy.

Yet, once scientists began to identify and decipher the bacteria that could pull off this conversion, they started finding them everywhere: in rivers, in soil, in deep-sea vents, even in tree bark. In some environments, the bacteria gulp down methane before it ever has a chance to reach the atmosphere.

The cumulative effect of all these methane-eating microbes, or methanotrophs, as they’re called, is tremendous.

“Globally, all of the methanotrophs on the planet are consuming many times the amount of methane that humans are releasing into the atmosphere,” said James Henriksen, an environmental microbiologist at Colorado State University.

That means Earth today would probably be even hotter without these creatures. It also means that if these microbes could be made to work a little harder, they might cool the planet, like climate-warrior cousins of other microorganisms that we use to produce drugs, kill crop pests and treat wastewater.

So far, though, methane eaters have proved tricky to wrangle. Some die with the slightest exposure to oxygen. Many work symbiotically with other organisms, like a tiny team. “They’re dependent on each other and almost certainly other factors, and we just don’t know exactly what they need,” said Jeffrey Marlow, an assistant professor of biology at Boston University.

That’s why Dr. Henriksen, Dr. Tierney and a genomic scientist, Krista Ryon, have been traveling to some of Earth’s most extreme environments: They want to know whether microbes in these places might be different enough — or just plain weird enough — to help reduce the harms that fossil-fuel use and industrial-age farming have done to the planet.

The three scientists and their collaborators have collected samples from hot springs around Colorado. They have dived to volcanic seeps off Sicily, Japan and Papua New Guinea. To organize their globe-trotting, they founded a nonprofit organization, the Two Frontiers Project, that is funded by Seed Health, a maker of probiotics, and other donors.

So far, Two Frontiers has mostly searched for bacteria that eat carbon dioxide, the main greenhouse gas that is warming Earth. One strain the team found off Sicily has proved so efficient that three gallons of it could theoretically absorb and lock away as much carbon dioxide as a tree, though researchers are still working out how to cultivate and deploy it at scale. Now, Two Frontiers is widening its hunt to devourers of methane, which has far greater heat-trapping power than carbon dioxide, though it stays in the atmosphere for less time.

Plenty of “really amazing” methane eaters are still waiting to be discovered, said Mary Lidstrom, a professor emeritus of chemical engineering and microbiology at the University of Washington. Those methanotrophs in tree bark? Scientists discovered them only a few years ago.

“Nature always surprises us,” Dr. Lidstrom said.

In Search of Purple Blobs

Aboard the dive boat, Dr. Tierney, Ms. Ryon and Gabriele Turco, a marine ecologist at the University of Palermo, awaited daybreak with giddy anticipation. The scientists had left port at midnight. After motoring west for four hours, they dropped anchor and gazed out over the dark water.

Someone flicked on a spotlight. At the edge of the boat, beads of gas bubbled up lazily from the depths — a possible sign of a methane seep.

This corner of the Mediterranean is virgin territory for biologists, said Dr. Turco, who also works for the National Biodiversity Future Center of Italy. “We have studied just a few parts of the tip of the iceberg,” he said.

After sunrise, the scientists pulled on their scuba gear and slipped into the water. Beneath their fins, a giant saucer of sand and sediment sloped up gently, forming the neat dome of a mud volcano.

The team started at the base, about 50 feet beneath the water’s surface. They collected samples of seawater, sediment and biomass — assemblages of microbes that could charitably be described as resembling mucus.

Dr. Tierney scanned the algae-furred boulders. Stuck to one rock was a fuzzy, chewing-gum-size wad of purple biomass. He bagged it excitedly.

A few minutes later, Dr. Turco spotted a mini mud volcano on the flank of the big one. Dr. Tierney uncapped a sample tube and corkscrewed it into the sand. Three fat bubbles erupted up. The little hill jiggled like flan when touched, a sign that it was suffused with gas and probably microbial life, too.

Up and down the big volcano, the researchers collected 22 samples, which they tucked into a cooler aboard their boat.

The next morning, they dived near the island of Elba among swaying meadows of sea grass and the hulking wreck of the Elviscot, a cargo ship that foundered on the rocks in 1972. To Dr. Tierney’s delight, he found another purple blob, which suggested that the two environments might be chemically similar despite being 25 miles apart.

All in all, the team gathered 43 samples, which they whisked back to land for processing in their Airbnb. This involved extracting the microbes from the plastic bags and injecting them into vials filled with different nutrient broths to see which environments the bacteria preferred.

The team’s setup was bare-bones. Samples were stored in the kitchen fridge, next to eggs and half-eaten croissants. To prevent contamination during processing, the scientists closed the windows and shut off the air-conditioning, turning the cramped bedroom into a sauna.

Dr. Tierney held up a bag containing one of the purple blobs — a clumpy mix, he reckoned, of bacteria and other matter akin to pond slime or spoiled food, perhaps with some algae jumbled in as well. “Let’s make sure we get as much of the actual goop as possible,” he said.

Once the microbes were nestled in new vials, the team sent the tiny travelers by FedEx to Dr. Henriksen’s lab in Colorado, where they’ve since been fed methane and allowed to grow.

Nature’s Surprises

Right now, the most technologically straightforward ways to cut the level of methane in the atmosphere have nothing to do with bacteria. They involve stopping methane from being released in the first place, by repairing leaks in pipelines, keeping organic waste out of landfills and changing the foods fed to cows.

At the moment, though, these low-tech fixes aren’t being used widely enough to bring down emissions. Some scientists hope microbes can help.

Dr. Lidstrom and her colleagues at the University of Washington are working on a device that would remove methane by pumping the air above emissions sites through a tank filled with microbial soup. The challenge, she said, is doing it at the scale of the atmosphere. Moving huge volumes of air would require lots of energy. If that energy is made by burning fossil fuels, then it partly cancels out the climate benefits of the endeavor.

Windfall Bio is a California start-up that uses methanotrophs to turn excess methane into useful things, like fertilizer. The company recently ran small trials of its technology at a landfill and at a dairy farm.

Mighty as microbes may be, the hard part about putting them to work for the climate is figuring out who foots the bill, said Josh Silverman, Windfall’s co-founder and chief executive. “People are not willing to pay for sustainability, and they’re not willing to pay for climate,” Dr. Silverman said. “So while it’s good to be aligned with that, that can’t be the only thing that drives it.”

He and his colleagues have been kicking around one idea: spraying cardboard boxes with microbes that could gobble up ambient methane as they’re shipped around the world.

“There’s a whole lot of surface area of cardboard boxes,” Dr. Silverman said. And if the boxes are composted, the bacteria could keep consuming methane from the compost pile, too.

The Two Frontiers team is still analyzing this summer’s specimens from Italy. The early results show promise: Among their samples is a symbiotic team of algae and bacteria that seems to use sunlight and methane to grow. This kind of microbial combination could be useful for capturing methane in rice fields, a major source of emissions.

For its next expedition, Two Frontiers is scoping out drier locales, ones with mud volcanoes on land. Dr. Marlow of Boston University is hoping to explore the seafloor off Angola and Namibia, where vents still hold mysteries — and probably new methanotroph species as well, he said.

Dr. Marlow’s dream in college was to work on Mars missions. He became interested in microbes in extreme environments because he thought they could help us understand life on other planets. Now, he said, “it’s clear that they matter a lot on Earth, too.”