From: Andy Soos, ENN
Published August 23, 2011 02:50 PM

Traveling Microbes

Microbes live in all parts of the biosphere where there is liquid water, including soil, hot springs, on the ocean floor, high in the atmosphere and deep inside rocks within the Earth's crust. Some recent studies indicate that airborne microbes may play a role in precipitation and weather. Eos, published by the American Geophysical Union, last month reported that bio-aerosols are "leading the high life." In the Eos article, David Smith of the University of Washington and colleagues argue that microbes are “the most successful types of life on Earth” and are the unacknowledged players in many planetary processes, particularly in the atmosphere.


There is some growing evidence that bacteria, fungal spores and viruses may spend large amounts of time - even their entire lives - in the air, riding clouds across the planet. And they don't just inhabit the clouds - they may also be creating them.  

"The ecology of the atmosphere is one of the last great frontiers of biological exploration on Earth," says Bruce Moffett of the University of East London.  

In 1979, Russell Schnell of the University of Colorado was in western Kenya wondering why the tea plantations there held the world record for hailstorms.  He discovered that tiny particles of dead and decaying leaves in the soil bore a close resemblance to the tiny particles around which hailstones formed. They seemed better adapted to the task even than man-made cloud seeding chemicals like silver iodide.

Mineral and salt particles are present in large numbers in clouds and can act as condensation nuclei. But many bacteria, as well as fungal spores and tiny algae, are the cloud condensation nuclei of choice because they can work at higher temperatures.

Bioprecipitation is the concept of rain-making bacteria and was proposed by David Sands from Montana State University before 1983. The formation of ice in clouds is required for snow and most rainfall. Dust and soot particles can serve as ice nuclei, but biological ice nuclei are capable of catalyzing freezing at much warmer temperatures. The ice-nucleating bacteria currently known are mostly plant pathogens. Recent research suggests that bacteria may be present in clouds as part of an evolved process of dispersal.

Bacteria present in clouds may have evolved to use rainfall as a means of dispersing themselves. The bacteria are found in snow, soils and seedlings in locations such as Antarctica, the Yukon Territory of Canada and the French Alps, according to Brent Christner, a microbiologist at Louisiana State University. It has been suggested that the bacteria are part of a constant feedback between terrestrial ecosystems and clouds. They may rely on the rainfall to spread to new habitats, in much the same way as plants rely on windblown pollen grains, Christner said, with this possibly a key element of the bacterial life cycle.

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