Bacteria Make Snow And Rain

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Main Category: Water - Air Quality / Agriculture
Also Included In: Infectious Diseases / Bacteria / Viruses
Article Date: 29 Feb 2008 - 12:00 PDT

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Scientists in the US have discovered that living organisms like bacteria play an important role in making rain and snow in the atmosphere. The discovery could help researchers understand the role of living organisms in the water cycle and lead to better climate forecasting, and solve problems of water shortage, said the researchers.

The discovery was made by Dr Brent C Christner assistant professor of Biological Sciences at Louisiana State University in Baton Rouge, and colleagues, and is written up in the 29 February issue of Science.

High in the earth's atmosphere, rain and snow clouds gather because of a process called ice nucleation. Small particles and suspensions of liquid and particles, aerosols to be precise, give water molecules a surface to cling to and clump together until eventually they form clouds.

For some time scientists have known about the role played by these various ice nucleators (IN) and how their presence eventually leads to precipitation, but what they did not know much about was where they came from and what they were made of.

Christner and colleagues looked at different types of ice nucleators (INs) at mid and high latitudes and discovered that most of them were biological in origin.

60 to 100 per cent of the INs that were bigger than 0.2 micrometers and working at temperatures higher than minus 7 degrees C, were biological, and many of them were bacteria.

Christner and colleagues said that the earth's atmosphere is full of highly active biological INs that play an important role in the water/precipitation cycle, and also not to be ignored is that they themselves come down in rain and snow.

Christner told the Associated Press that bacteria were by far the most active ice nucleators in nature. He and his colleagues took snow samples in Antarctica, France, Montana (US) and the Yukon (Canada).

They found that in some of the samples 85 per cent of the INs were bacteria. The French samples had the highest concentration of bacterial INs, followed by Montana and the Yukon. Even the samples from Antarctica contained bacteria, but at much lower levels.

Strangely enough, the most common bacteria they found in the samples was Pseudomonas syringae, which infects plants like tomatoes and beans and has been mostly considered a candidate for elimination because of this, but as Christner said to the Associated Press, perhaps that is now not such a good idea.

What would happen to the process of cloud formation if a principal catalyst were to be eliminated? Would it simply be replaced by particles like soot and dust?

An interesting point he raised was what if plants in dry areas infected with Pseudomonas syringae were actually helping to increase the chance of rainfall by putting more INs into the atmosphere?

What science is revealing to us more and more is that the atmosphere is not an "inert" stratum, but a complex biomass intricately interwoven with processes that affect planetary life, such as the water cycle.

The authors suggest that deciphering some of these "feedback" mechanisms between the biosphere and climate could have important implications for climate forecasting and understanding the way that plant pathogens and other microorganisms travel around the globe.

"Ubiquity of Biological Ice Nucleators in Snowfall."
Brent C. Christner, Cindy E. Morris, Christine M. Foreman, Rongman Cai, and David C. Sands.
Science 319 (5867), 1214, (29 February 2008).
DOI: 10.1126/science.1149757

Click here for Abstract.

Source:Science, Associated Press, Louisiana State University.

Written by: Catharine Paddock, PhD
Copyright: Medical News Today
Not to be reproduced without permission of Medical News Today

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