Atmospheric microbes have the capacity for global dispersal and may modify climate by affecting cloud development processes, cloud chemistry, and precipitation generation. For instance, aerosolized ice-nucleating prokaryotes are ubiquitous in snow and rain, and have an atmospheric residence period ~ 20 times shorter than other microbes. This characteristic may provide ice-nucleating species with a rapid return time to surface environments, facilitating their reproduction and growth. Despite these intriguing properties, little is known about precipitation-associated microbial assemblages, and their associations with abiotic factors.
We sampled precipitation events for airborne microbes at three locations (Virginia, Idaho, and Louisiana) across four seasons (spring, summer, winter, fall). We obtained Operational Taxonomic Unit (OTU) level community summaries of samples based on amplifications of the bacterial 16S rRNA gene sequence, and sequencing with the illumina® MiSeq platform. Meteorological data associated with rain events were obtained from Geostationary Operational Environmental Satellite-East (GOES-East), among other sources.
Using a variety of analytic approaches, including Permutation Multivariate Analysis of Variance (PERMANOVA) and NMDS ordination, we found that Idaho and Virginia microbial communities were homogenous within each location, and were highly distinct from other sites. Louisiana samples had higher levels of alpha and beta-diversity, compared to Idaho and Virginia. Within geographic location, patterns in community composition were evident among seasons. Furthermore, patterns in site and season could be related to meteorological characteristics of the precipitation events themselves. Fisher's exact tests identified differences in rain event air mass origins (i.e., combinations of: continental, maritime-Atlantic, maritime-Pacific, polar, and tropical) for sites, whereas stratiform and convective weather events and altitudinal classes occurred at different frequencies during different seasons. Our investigation furthers understanding of microbial dispersal in the atmosphere by identifying simultaneous patterns of spatial and temporal community variation at a continental scale.