At the center of a snowflake, unromantically, is bacteria. Ice in the atmosphere is formed around a nuclei and 85% are bacteria. Bacteria are by far the most active ice nuclei in nature.
Bugs in the sky? Believe it.
[AP story] Brent C. Christner at Louisiana State University studies snow and ice from Antarctica, France, Montana and the Yukon and found that Pseudomonas cause moisture in a cloud to condense. Killed bacteria are used as an additive in snow making at ski resorts.
Bio-precipitation could affect many things, from agriculture and water availability to local climate and even global warming. For example, a reduced amount of bacteria on crops could affect the climate. Because of the bio-precipitation cycle, overgrazing in a dry year could actually decrease rainfall, which could then make the next year dryer.