Scientists find evidence of "rain-making" bacteria

WASHINGTON, Feb. 29 - A team of scientists from the United States and France have found evidence that rain-making bacteria are widely distributed in the atmosphere.

These biological particles could factor heavily into the precipitation cycle, affecting climate, agricultural productivity and even global warming. The new finding is published in the journal Science on Friday.

The research team examined precipitation from global locations and demonstrated that the most active ice nuclei -- a substrate that enhances the formation of ice -- are biological in origin. This is important because the formation of ice in clouds is required for snow and most rainfall.

Researchers have found biological ice nuclei in precipitation samples from Antarctica to Louisiana -- they're ubiquitous.

Dust and soot particles can serve as ice nuclei, but biologicalice nuclei are capable of catalyzing freezing at much warmer temperatures.

The concept of rain-making bacteria isn't far-fetched. Many ski resorts use a commercially available freeze-dried preparation of ice-nucleating bacteria to make snow when the temperature is just a few degrees below freezing.

What makes this research more complicated is that most known ice-nucleating bacteria are plant pathogens. These pathogens, which are basically germs, can cause freezing injury in plants, resulting in devastating economic effects on agricultural crop yields.

"As is often the cases with bacterial pathogens, other phases of their life cycle are frequently ignored because of the focused interest in their role in plant or animal health," said Brent Christner, one of the study author from Louisiana State University." Transport through the atmosphere is a very efficient dissemination strategy, so the ability of a pathogen to affect its precipitation from the atmosphere would be advantageous in finding new hosts."

It is possible that the atmosphere represents one facet of the infection cycle, whereby the bacteria infects a plant, multiplies, is aerosolized into the atmosphere and then delivered to a new plant through atmospheric precipitation.

"The role that biological particles play in atmospheric processes has been largely overlooked. Our results provide an impetus for atmospheric scientists to start thinking about the role these particles play in precipitation," said Christner.