A UNIQUE community of bacteria living 300 metres beneath the floor of the Pacific Ocean has been investigated for the first time. This is the most detailed study so far of life within the oceanic crust, and it hints at a massive and virtually unknown ecosystem that runs independently of the Sun鈥檚 energy.
Almost every microbe found there belongs to a completely new species. 鈥淚t鈥檚 a very exotic group of organisms,鈥� says Stephen Giovannoni at Oregon State University.
Giovannoni鈥檚 team took their samples from a borehole off the coast of Oregon, near the centre of the Juan de Fuca ridge. The hole passes through 250 metres of sediments and 50 metres of basaltic crust, and was originally drilled in 1996 to yield geological data. But it was also a unique opportunity to find out more about microbes living in the crust.
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Fluid at the bottom of the borehole is under high pressure and at a temperature of 65 掳C. Giovannoni and his team dredged some of this fluid. They have not yet grown any of the bugs they found, but they classified them by comparing their DNA sequences with known species (Science, vol 299, p 120). Some species have DNA similar to microbes from hydrothermal vents, but the borehole community has almost nothing in common with other deep-sea bacteria. The most abundant species is similar to Ammonifex degensii, a bacterium that gets its energy by reacting hydrogen and nitrate together to form ammonium. The team found lots of ammonium in the borehole fluid, supporting the idea that many of the newly found bugs get their energy this way too.
The fluid also contained an abundance of long-chain organic molecules, though where these come from remains a mystery. Their carbon isotope composition suggests that they are not produced by a biological process.
Giovannoni says the study offers a glimpse of a vast ecosystem that we know almost nothing about. 鈥淭his is just a snapshot of what is probably a rich and variable environment,鈥� he says. Russell Vreeland, who studies rock microbes at West Chester University of Pennsylvania, agrees. 鈥淭he biosphere is a whole lot larger than we thought it was,鈥� he says.
Studying such extreme environments might shed light on the possibility of life on other planets. Mars, for example, appears dead on the surface, but deeper down there is almost certainly liquid water that could harbour life. 鈥淚t makes it more and more likely that when you go to another planet you are going to find something, even though it looks dead,鈥� says Vreeland.
