Bacteria that can turn creatures into stone do exist
GREEK mythology can boast of some
truly weird creatures. Centaurs - the
furious half- man- half- horse warring
class, Hydra, a three-headed monster
and many more. But none is as frightening as the three snake-haired Medusa,
one look from whom could turn people
into stone. Well, as Mother Nature
would have it, there actually is a biological version of these femme fatales.
Bacteria that can turn mud to rock do
exist. These Medusa bacteria quickly
fossilise the remains of mud-dwelling
animals. An amazing chemical reaction
performed by these bacteria can fossilise
remains of animals before rotting starts
(Science, Vol 282, 1665).
The formation of sedimentary rocks is usually an excruciatingly slow process, taking at least a million years. But the two bacteria, discovered by a research team led by Max Coleman, sedimentologist at the University of Reading, USA, can do the job in as little as six months. While digging survey trenches in Norfolk salt marshes, Coleman noticed weird stony nodules buried in the mud. "We found rocky lumps in what was otherwise soft," he says. Some were even as large as footballs. Coleman has established that a pair of bacteria collaborate to create these stony nodules. The first, a species of Dseulfobacter, gets energy by eating' sulphates in seawater and reducing them to hydrogen sulphide. The second, Desulfovbrio desulfuricans (D desulfuricans), also does the same thing. But when D desulfuricans's environment contains too much hydrogen sulphide, it starts reducing iron compounds, converting iron (Fe'+) ions to Fe2l. It also reacts with hydrogen sulphide and other salts to create stony deposits of iron sulphide and iron carbonate. The reactions are not reversible, but if the nodules are exposed to air, the surface layer of iron undergoes further oxidation, forming rust. The nodules could be a rich source of fossils.
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