Halobacteria: the evidence for longevity |
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Authors: | W D Grant Renia T Gemmell Terry J McGenity |
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Institution: | (1) Department of Microbiology and Immunology, University of Leicester, P.O. Box 138, Leicester, LE1 9HN, UK Tel. +44-116-252-2948; Fax +44-116-252-5030 e-mail: WDG1@le.ac.uk, GB;(2) Oxford Centre for Environmental Biotechnology, Institute of Virology and Environmental Microbiology, Mansfield Road, Oxford, OX1 3SR, U.K., GB;(3) Postgraduate Institute for Sedimentology, University of Reading, Whiteknights, Reading, RG6 6AH, U.K., GB |
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Abstract: | Subterranean salt deposits are the remains of ancient hypersaline waters that presumably supported dense populations of halophilic
microorganisms including representatives of the haloarchaea (halobacteria). Ancient subterranean salt deposits (evaporites)
are common throughout the world, and the majority sampled to date appear to support diverse populations of halobacteria. The
inaccessibility of deep subsurface deposits, and the special requirements of these organisms for survival, make contamination
by halobacteria from surface sites unlikely. It is conceivable that these subterranean halobacteria are autochthonous, presumably
relict populations derived from ancient hypersaline seas that have been revived from a state of dormancy. One would predict
that halobacteria that have been insulated and isolated inside ancient evaporites would be different from comparable bacteria
from surface environments, and that it might be possible to use a molecular chronometer to establish if the evolutionary position
of the subsurface isolates correlated with the geological age of the evaporite. Extensive comparisons have been made between
the 16S rRNA genes of surface and subsurface halobacteria without showing any conclusive differences between the two groups.
A further phylogenetic comparison exploits an unusual feature of one particular group of halobacteria that possess at least
two heterogeneous copies of the 16S rRNA gene, the sequences of which may have been converging or diverging over geological
time. However, results to date have yet to show any gene sequence differences between surface and evaporite-derived halobacteria
that might arguably be an indication of long-term dormancy.
Received: January 22, 1998 / Accepted: February 16, 1998 |
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Keywords: | Halobacteria Haloarchaea Evaporites Dormancy 16S rRNA genes rRNA gene heterogeneity Salt mines Longevity |
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