Surviving in salt?

In the manner of Count Dracula’s dogged refusal to shed his mortal coil by hiding from sunlight, is it conceivable for primitive organisms to be immortal by being protected from UV radiation?  That it might be possible emerged from the revival of bacteria trapped in fluid inclusions in Permian rock salt by Russell Vreeland and William Rozenzweig of West Chester University in Pennsylvania (see Earth Pages, November 2000, The undead).  Despite taking stringent precautions to avoid any contamination of their samples by modern bacteria, Vreeland and Rozenzeig’s claim has been fiercely challenged.  It is possible that the dormant bacteria could have entered the salt in much younger solutions permeating the deposit (incidentally one of the most stable tectonically and hydrogeologically – it is the prospective site for burial of US radioactive wastes).

Vreeland’s team  found 4 bacterial strains – all salt-tolerant halobacteria – but have genetically fingerprinted only one so far.  It is related to a modern genus living in the Dead Sea that forms spores.  The minute fluid inclusions from which samples came have insufficient energy and nutrients to have sustained cell growth and division.  The inactivity involved in spore formation, combined with the slowing down of biological processes by dense brines in the inclusions, might just allow immensely long survival for 250 Ma without breakdown of the DNA essential for revivable dormancy.  Hydrogen diffusing into the salt and biological materials could have played a role in maintaining DNA’s integrity.  One snag is that the DNA sequence of the revived bacteria is 99% identical to that of its closest modern relative.  Using the theory of molecular clocks, they should have been different by 5 to 10%.  Yet, says Vreeland, salt deposits continually add to the surface environment, being soluble.  Any dormant bacteria within them would replenish fully living stocks in similar environments to those which formed the salt originally.  Such continual addition might preserve ancient genetics, that would otherwise evolve steadily.

Aside from giving comfort to proponents of life spreading throughout the universe as spores adrift on dust driven in the manner of a solar sail, the results encourage probing of older salt deposits, which go back in almost undisturbed form to the Mesoproterozoic.

(Source:  Knight, J.  The Immortals.  New Scientist, 28 April 2001, p. 36-39).


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