Bacteria 'abound in hailstones'

[Still Waters]

A study of hailstones has found large numbers of bacteria at their cores.

The find lends credence to the "bio-precipitation" idea, which suggests that bacteria are actively involved in stimulating precipitation.

The bacteria have protein coatings that cause water to freeze at relatively warm temperatures.

Researchers at the American Society for Microbiology meeting suggest bacteria may have evolved to use the water cycle to facilitate their own dispersal.

The micro-organisms that can be found in precipitation such as snow have been studied since the 1960s.

One bacterium that has appeared in many contexts is Pseudomonas syringae, which expresses a protein on its surface that encourages an orderly arrangement of water molecules.

That in turn acts as a "nucleation" site, stimulating the formation of ice at temperatures far higher than those normally required.

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