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Appl. Environ. Microbiol., Sep 1996, 3405-3412, Vol 62, No. 9
V Boivin-Jahns, R Ruimy, A Bianchi, S Daumas and R Christen
The presence of bacteria in a deep clay sediment was analyzed in a 20-m-
long core horizontally drilled from a mine gallery at a depth of 224 m in
the Boom clay formation (Mol, Belgium). This clay deposit is the result of
a marine sedimentary process that occurred 35 million years ago. Bacterial
activities were estimated by measuring respiration on [14C]glucose. Using
the same samples, universal primers for the genes coding for eubacterial
16S rRNA were used to amplify extracted DNA. PCR products were then cloned,
sequenced, and analyzed by molecular phylogeny. Our data showed a decrease
in bacterial densities as a function of distance from the gallery, with few
bacteria detectable by culture at more than 80 cm from the gallery wall.
PCR experiments showed the presence of bacteria in all samples, and
phylogenetic analyses were then used to tentatively identify these
organisms. Because of low bacterial densities in deep clay samples, direct
counts and enumeration of viable bacteria on diverse culture media remained
negative. All experiments, both cultures and PCR, demonstrated the
difficulty of analyzing samples that contain only a few poorly active
bacteria as it is difficult to avoid a small contamination by active
bacteria during sampling. Since the porosity of the Boom clay formation is
less than the expected size of bacteria, it is possible that some of the
bacteria present in this 35-million-year-old deep clay deposit derive from
cells initially trapped during the sedimentation process.
Copyright © 1996, American Society for Microbiology
Bacterial diversity in a deep-subsurface clay environment
Observatoire Oceanologique, Centre National de la Recherche Scientifique and Universite Paris, France.
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