Bacteria in soil may be dispersed in the air via raindrops according to a study published in Nature Communications this week. This is a new mechanism that sheds light on our understanding of how bacteria may be spread over long distances.
Previous work has shown that as a raindrop impacts soil, aerosols (suspended water droplets) are generated. Soils can act as an intermediate home for bacteria, but it has been unclear how bacteria might be transferred to the atmosphere as it was believed that they would not survive the aerosolization process.
Using high-speed cameras, fluorescent imaging and modelling experiments, Cullen Buie and colleagues find that a single raindrop can transfer 0.01% of bacteria on the soil surface to the atmosphere, where it can survive for more than one hour. Although the percentage of bacteria transferred to the atmosphere seems low, the team calculates that global precipitation may transport between 1.6% and 25% of the total bacteria from land depending on differing soil types and local climate. Aerosolization is visualized in three non-pathogenic strains of soil bacteria.
Although these findings explain how bacteria can be transferred to the atmosphere, which has implications for the climate, agricultural productivity and human health, there is no evidence that this mechanism promotes diseases after heavy rain.