Snowflakes Aren’t Innocent and Fluffy—They’re Bacteria Bombs from the Sky

When Montana State University plant pathologist David Sands first proposed that some bacteria that infect plants could spread over great distances through falling precipitation, some thought his idea was crazy. But new research says Sands' idea actually holds water. Bacteria, including one species known to infect tomato and bean plants, are found in greater abundance in freshly fallen snow than previously thought, says Brent Christner at Louisiana State University, who led the new research. Christner examined snow from sites with lots of vegetation nearby (France) and places with no vegetation (like Antarctica). He found bacteria in snow no matter where he looked. In some samples, 85 percent of the particles found in the snow were bacterial. Snowflakes typically form around a nucleator—a dust particle or pollen grain in the air (more fun facts about snow from DISCOVER's "20 Things"). At temperatures above 14 degrees Fahrenheit, bacteria are the most efficient nucleators because the components of bacterial cell walls make terrific scaffolds for building snowflakes, says Christner. So snowflakes made at these temperatures may have a living bacterium—or a not-so-living bacterium—or a bit of fungi or pollen at their center. Rest assured, you won't come down with salmonella by catching snowflakes on your tongue. Christner says there’s no evidence that bacteria that can make people sick are passed around this way. But the finding changes the way scientists look at precipitation on earth. The age-old textbook diagrams showing water evaporating into the air, moving over land, and falling as rain or snow may now need to be redrawn to take into account the effects of bacteria borne aloft. So could we summon forth a huge snowfall, setting the stage for an ideal ski weekend, by launching a tub of atomized microbes into the air? Christner says it is conceivable but very speculative. One can always hope...