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Methane-Munching Microbes Take a Bite Out of Warming

Sean Markey
for National Geographic News
October 18, 2006
 
If you're enjoying the weather today—or least find it more
hospitable than the methane-fueled scorcher on, say, Venus—thank
a microbe.

Specialized creatures gobble up much of the methane belched from underwater mud volcanoes, a new study says. Methane, a greenhouse gas, is a key driver of global warming.

Seven years ago scientists discovered the unpoetically named ocean bacterium ANME-1, the first organism found to feed on methane.

Now researchers are learning more about how that bacterium and similar organisms behave and influence Earth's methane cycle.

Writing in tomorrow's issue of the journal Nature, the team describes three communities of methane-munching microbes found on an Arctic undersea mud volcano in the Barents Sea above western Russia (Russia map).

These creatures include bacteria, worms, and a previously unknown species from the archaea group of single-celled life-forms. Each creature has an uncommon metabolism that depends on the energy stored in methane, and each processes the gas in a unique way.

While the creatures' specific biochemistries remain unclear, one microbe uses oxygen to break down methane. Another teams up with unrelated bacteria species and uses sulfate to convert the greenhouse gas into energy.

Methane Filters

Thanks to the microbes, a significant portion of the methane belched from deep below the seafloor by the Haakon Mosby Mud Volcano, for example, never reaches the ocean.

That's good news for many-celled landlubbers worried about global warming. Atmospheric methane is nearly 20 times more powerful than carbon dioxide when it comes to trapping heat from the sun.

"Methane-consuming microorganisms … are critical to maintaining a healthy climate on Earth," said study co-author Antje Boetius, a microbiologist at the Max Planck Institute for Marine Microbiology in Bremen, Germany.

Boetius helped discover the bacterium ANME-2 in 2000.

Much about Earth's methane cycle, particularly what happens below the ocean, remains unknown. But scientists have begun to slowly piece together the puzzle, thanks to novel lab techniques, undersea robotics, and other new technologies.

"Microbes control probably 90 percent of the total methane flux in the oceans," Boetius said, and "probably half of all … natural atmospheric emissions."

Methane-munching bacteria have now been found in every ocean on Earth. In many places they prevent the greenhouse gas from ever escaping the seafloor, let alone the ocean surface, she says.

William Ussler is a geochemist at the Monterey Bay Aquarium Research Institute in California. He says that precisely how much methane cycles between the ocean and the atmosphere has "been a source of speculation."

But one thing is clear: Earth has a lot of methane—nearly twice the amount of all other fossils fuels combined, including coal, oil, and natural gas deposits.

Much of this methane lies in ocean sediments in the form of a gas hydrate. This white, icelike solid is made of frozen methane gas and water and forms under intense pressure at depths of about 1,600 feet (500 meters) or more.

"The amount of methane in the atmosphere is small relative to the amount in the ocean," Ussler said.

There may be 10,000 times as much methane in the ocean than there is in the atmosphere, according to some estimates.

"And so a small change in the size of the methane reservoir in the ocean can double or triple the amount of methane in the atmosphere very quickly," Ussler added.

Spin-Off Technology?

In recent years researchers have identified a raft of bacteria with unusual metabolisms previously unknown to science.

Some microbes breathe rust. Others break down uranium or produce electricity from mud.

Scientists have harnessed a number of these creatures to develop new technologies—cleaning up radioactive groundwater, for example, or powering experimental robots with dead flies or rotten apples.

But study co-author Boetius says it's unlikely the discovery of methane-munching microbes will yield an easy way to zap the global-warming greenhouse gas.

For starters, the microbes can't be grown in the lab, so the chemistry behind their unusual metabolisms remains a mystery.

The microbes are extremely slow growing too, she says, and therefore unsuited to the pace of most scientific research.

"They are not like E. coli that can duplicate every 20 minutes. But rather, they probably have generation times of months or even years," Boetius said.

And when it comes to addressing global warming, time, it seems, is in increasingly short supply.

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