Tiny bacteria hiding out in a witches' brew of bubbling mud not only thrive in the searing-hot slurry but also chow down on its methane.
Two papers published online this week in the journal Nature describe these mud-loving microbes, the hardiest bacteria identified to date. Found living in mud volcanoes and other geothermal hideouts, the bacteria feast on methane, considered the second most abundant greenhouse gas behind carbon dioxide. While carbon dioxide makes up the majority of greenhouse gases in the atmosphere, methane traps about 20 times more heat and so is a critical global warmer.
And so in addition to expanding the conditions where one might find extremophiles, the discovies have implications for the global methane cycle. These specialized bacteria could help to suck up methane from the Earth's crust that would otherwise spew into the atmosphere.
Mud pits
The hellish temperature and pressure conditions beneath the Earth's surface can turn rock into goopy mud, which along with a soup of gases (including methane) and other chemicals, can stream gently (or eject violently) from surface vents called fumaroles. These "mud volcanoes" support a range of conditions, with some areas reaching temperatures of 158 degrees Fahrenheit (70 degrees Celsius) and pH's close to that of battery acid.
Mike Jetten of Radboud University Nijmegen in the Netherlands and his colleagues discovered a bacterium dubbed Acidimethylosilex fumarolicum in a fuming vent in the Solfatara volcanic area near Naples, Italy.
Lab experiments revealed A. fumarolicum could grow at a very acidic pH, as low as 0.8, and at a temperature of about 130 degrees F (55 degrees C), consuming methane for energy. (The pH scale ranges from 0 to 14, from acidic to basic. Water has a neutral pH of 7; battery acid and hydrochloric acid have pH's below 1, and the pH of household bleach can reach about 12.5.)
The bacteria can use oxygen too, but their muddy habitat is nearly devoid of such luxuries, making for a stressful life.
"The only oxygen the bacteria get is from the bubbling of the volcano, which puts air into the liquid," Jetten told LiveScience. "They are always stressed for air, so they're always living under oxygen limitation. The ecosystems themselves are completely devoid of oxygen, so every molecule that enters is immediately consumed."
Another extreme-loving methane consumer was discovered at Hell's Gate (Tikitere) in New Zealand. Peter Dunfield of GNS Science, a New Zealand government-owned research organization, and his colleagues found that Methylokorus infernorum could thrive at a pH as low as 1.5 and temperatures of about 140 degrees F (60 degrees C).
Methane munchers
Both bacterial finds top the hardiest methane munchers identified to date. Until now, the lowest pH found to support "methanothrophs" was in peat bogs, where bacteria thrived down to a pH of about 4.
How exactly the bacteria are able to withstand the harsh habitats while consuming methane is still a bit of a mystery. Genetics do play a role. The research teams analyzed the genomes for the two bacterial species, finding some novel systems that likely allow the methane-consuming microbes to thrive in harsh conditions.
"The new bacterium has a completely new repertoire of genetic elements to do this job," Jetten said of A. fumarolicum. "And it's also quite different from the known methane-oxidizing bacteria."
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