A good rain can have a cleansing effect on the land. But an MIT study published today in Nature Communications reports that, under just the right conditions, rain can also be a means of spreading bacteria.
Using high-resolution imaging, researchers from MIT’s Department of Mechanical Engineering observed the effect of raindrops falling on dry soil laden with bacteria. When falling at speeds mimicking those of a light rain, at temperatures similar to those in tropical regions, the drops released a spray of mist, or aerosols. Each aerosol carried up to several thousand bacteria from the soil. The researchers found the bacteria remained alive for more than an hour afterward.
If this airborne bacteria were lofted further by wind, it could travel a good distance before settling back on the ground to colonize a new location, says Cullen Buie, associate professor and the Esther and Harold E. Edergton Career Development Chair in the Department of Mechanical Engineering.
“Imagine you had a plant infected with a pathogen in a certain area, and that pathogen spread to the local soil,” Buie says. “We’ve now found that rain could further disperse it. Manmade droplets from sprinkler systems could also lead to this type of dispersal. So this [study] has implications for how you might contain a pathogen.”
Furthermore, the team calculated that precipitation around the world may be responsible for 1 to 25 percent of the total amount of bacteria emitted from land.
Buie’s co-authors are postdoc Zhifei Ge and former postdoc and lead author Youngsoo Joung.