Tuesday, December 11, 2007

Methane eaters from the gates of hell

Cows produce lots of methane, but our planet itself exhales large amounts of the greenhouse gas, too. Certain bacteria can use the geologically produced methane as a fuel and turn much of it into biomass – a very laudable contribution to our current concern of minimising greenhouse gas emissions. Soils in volcanic areas are often hot and acidic, so any bacteria gobbling up methane in those areas would have to be adapted to these extremes. Decades of research have failed to identify any species that can thrive on methane under such conditions, but now two independent research groups have simultaneously found two of them, and hints that there may be many more.

Researchers from Nijmegen in the Netherlands and Naples, found Acidomethylosilex fumarolicum in hot, acidic volcano mudpots in Italy. This bacterium can thrive in extremely acidic conditions, down to pH 0.8, and its preferred temperature is around 55 deg. C. Surprisingly, it is unrelated to any of the known methanotrophic bacteria, which are all found in one of two large phylogenetics groups, the alpha and the gamma proteobacteria. A. fumarolicum appears to belong to the phylum verrucomicrobia, only very distantly related to proteobacteria. The microbe hunters tracked it down by looking for a key enzyme of methane metabolism, methane mono-oxygenase. Eventually they found three copies of the corresponding gene in A. fumarolicum, but they were quite different from the ones in known methane eaters, explaining why the extreme bug hasn’t been found before.

Conversely, microbiologists from New Zealand, Hawaii, and China, using samples from a geothermal area known as Hell’s Gate in New Zealand, cultivated a microbial strain first, which they baptised Methylokorus infernorum, and which can metabolise methane at pH as low as 1.5. Being unable to identify the methane mono-oxygenase enzyme in this species, they went on to sequence its genome (as you do, these days) and found three copies, again. Like A. fumarolicum, this new methane eater is classified off the beaten track of methanotrophs, in the phylum of Verrucomicrobia.

Now that we know what acid-loving methane eaters look like (genetically speaking), there may be many more new species to follow. The Dutch group has already looked at unrelated samples from Yellowstone National Park (US) and found evidence that similar extremophiles live there, as well. Although they have failed to be discovered for decades, these bugs may in fact be widespread.

A. Pol et al., Nature 2007, 450, 874.
P. F. Dunfield et al., Nature 2007, 450, 879.

Related books:
Life on the Edge: Amazing creatures thriving in extreme environments
Astrobiology: a brief introduction

NB: This story is a blog-exclusive one. From now on, I'll label such stories with the tag "sciencenews", while those published elsewhere have the tag "sciencejournalism".

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