BEIJING, Feb. 29 (Xinhuanet) -- Atmospheric scientists have long known that most snow and rain forms in chilly conditions high in the sky, under most conditions, the moisture needs something to cling to in order to condense.

Now, a new study shows a surprisingly large share of those so-called "something to cling to" turns out to be bacteria that can affect plants, according to Friday's edition of the journal Science.

Farmers harvest vegetable in the snow-covered fields in Dayu township of Hefei, capital of east China's Anhui province, Jan. 27, 2008. A rare heavy snowfall hit the city recently. The local government urged vegetable growers in the suburb to speed up vegetable transportation in order to meet the market demand.

"Bacteria are by far the most active ice nuclei in nature," said Brent C. Christner, an assistant professor of biological sciences at Louisiana State University.

Christner and his colleagues sampled 20 snow samples from Antarctica, France, Montana and the Yukon.

Christner said in some samples bacteria amounted to 85 percent of the nuclei. The bacteria were most common in France, followed by Montana and the Yukon, and was even present to a lesser degree in Antarctica.

Pseudomonas syringae was found to be the most common bacteria, which can cause disease in several types of plants including tomatoes and beans.

The focus on Pseudomonas in the past has been to try and eliminate it, Christner said, but now that it turns out to be a major factor in encouraging snow and rain.

"The question is, are they a good guy or a bad guy," he said, "and I don't have the answer to that."

What is clear is that Pseudomonas is effective at getting moisture in a cloud to condense, Christner pointed out. Killed bacteria are even used as an additive in snow making at ski resorts.