Bacteria thrive deep under sea floor

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.