Bacteria thrive deep under sea floor

February 26, 2005 Analysis of sediments taken from hundreds of metres beneath the ocean floor has shown them to contain living microbes. According to a study produced by a team of researchers supported by the International Ocean Drilling Program, this is the first time that microbes have been found in abundance at such depths.

Scientists have long speculated about how much of the bacterial content of the sediments is biologically active. Techniques used to stain the bacteria and identify them could not previously discriminate between live and dead cells. For this study a new technique that could distinguish between alive and dead cells was used.

The results were surprising. The sediments, some of which had been collected from up to 800 metres from beneath the sea floor and are said to be up to 16 million years old, contained between 10-30% living bacteria. Scientists estimate that between 60-70% of all bacteria are living deep beneath the surface, far from any sunlight.

"We didn't have clear evidence that bacteria there were alive until now," said ecologist and team member Lev Neretin of the Max Planck Institute for Marine Biology in Bremen, Germany. According to calculations, the populations of bacteria multiply at the same rate as their surface cousins and contribute significantly to the balance of greenhouse gases, consuming and producing CO2. They also contribute methane via a metabolic process that does not require oxygen.

"Because they play such a major role in the biochemical processes in the subsurface, clearly they are driving lots of reactions that produce the chemical steady state on Earth," said Dr John Parkes, one of the original co-authors of the paper which appeared in Nature magazine, "possibly we might not have oil and gas formations without them."

How could these bacteria get so deep beneath the ocean floor? "The only reasonable way is for them to be buried there," says Bo Thamdrup, a microbiologist from the University of Southern Denmark, Odense. The extremes of temperature and pressures tolerated by these bacteria add weight to the assertion that microbes may flourish in the extreme conditions of other planets.

"It is well known that bacteria living in deep oceans have special adaptations to help them survive," says Thamdrup. "I'm sure these bacteria have special adaptations too." A full genetic analysis may soon reveal them.