Recent studies on bacterial populations and processes in subseafloor sediments: A review |
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Authors: | R John Parkes Barry A Cragg Peter Wellsbury |
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Institution: | (1) Department of Earth Sciences, University of Bristol, Wills Memorial Building, Queens Road, Bristol BS8 1RJ, UK Fax: +44-117-9253385 e-mail: J.Parkes@bris.ac.uk, GB |
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Abstract: | Subsurface bacteria also occur in hydrothermal sediments with large temperature gradients (up to 12 °C/m) and with population
numbers similar to non-hydrothermal sites at temperatures from psychrophilic to mesophilic. At greater depths and temperatures,
populations decline rapidly, but they are still significant up to hyperthermophilic temperatures and are even stimulated by
subsurface seawater flow. These results suggest that temperature alone does not limit bacteria in non-hydrothermal sediments
until about 4 km, and evidence exists that bacterial processes may even be sustained by interaction with thermogenic processes
as temperatures increase during deep burial.
Experiments demonstrate that in the presence of readily degradable organic substrates, actively growing bacteria can move
faster than sediment deposition; hence, these bacteria are not necessarily trapped and buried. However, bacterial growth decreases
with depth to such an extent that subsurface bacteria would not be able to keep up with sedimentation rate and hence would
be buried. In some circumstances, such as in sapropel layers with high organic matter in the Mediterranean, bacteria may be
buried within a specific deposition horizon. Subsurface bacteria can utilize old and recalcitrant organic matter, but only
very slowly, and they seem to have a strategy of high biomass and low growth rate, commensurate with their geological habitat
of generally low energy flux.
Received, March 1999/Revised, August 1999/Accepted, November 1999 |
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Keywords: | microbial processes subseafloor sediments bacteria |
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