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.


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Bacteria thrive deep under sea floor