May 25, 2011

Do Bacteria Contribute To Weather Conditions?

Airborne microorganisms may be responsible for weather events, according to a study that found a high concentration of bacteria at the center of hailstones.

Alexander Michaud from Montana State University in Bozeman presented the findings of the study at the 111th General Meeting of the American Society for Microbiology in New Orleans.

Researchers analyzed hailstones that measure over 5 centimeters in diameter (about 2 inches) which were collected on the University campus after a storm in June 2010.

Each hailstone was then separated into 4 layers and the meltwater of each layer was analyzed by researchers. The results found that the inner cores of the hailstone contained the highest concentration of culturable bacteria.

Michaud says, "Bacteria have been found within the embryo, the first part of a hailstone to develop. The embryo is a snapshot of what was involved with the event that initiated growth of the hailstone."

Bioprecipitation, the study of how bacteria may cause rain, snow and hail, is a growing field of study, which suggests that in order for clouds to make ice, from which snow falls, a particle called ice nuclei (IN) must be present for the ice crystals to grow around.

"In order for precipitation to occur, a nucleating particle must be present to allow for aggregation of water molecules," Michaud says. "There is growing evidence that these nuclei can be bacteria or other biological particles."

Although a diverse range of particles contribute to the IN, the most active naturally occurring IN are of biological origin that are capable of catalyzing ice formations at temperatures near -2 degrees Celsius, according to the study.

The most commonly studied biological IN is the plant pathogen Psuedomonas syringae.

"Ice nucleating strains of P. syringae possess a gene that encodes a protein in their outer membrane that binds water molecules in an ordered arrangement, providing a very efficient nucleating template that enhances ice crystal formation," says Brent Christner of Louisiana State University who also presented at the meeting.

He also says, "Aerosols in clouds play key roles in the processes leading to precipitation due to their ability to serve as sites for ice nucleation. At temperatures warmer than -40 degrees Celsius ice formation is not spontaneous and requires an IN."


Image Caption: Large hailstones up to 5 centimeters (2 in) in diameter with concentric rings. Credit: Soon Chun Siong/Wikipedia 


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