The airborne microbiome: consistent seasonal trends in the aeroplankton assemblage. Airborne microbiome

Microbes represent an important component of the atmospheric aerosols with the potential to impact human health and atmospheric dynamics. In addition, aerosols represent a potential successful mechanism for worldwide microbial dispersal. However, current knowledge on the temporal dynamics of airborne microbes on the long-term is negligible. In this study we applied high-throughput sequencing techniques (16S rRNA and 18S rRNA genes amplicons) to follow microbes (bacteria, archaea, protists and fungi) present in c. 150 rain and snow samples collected periodically for seven years in a high elevation mountain site of the Central Pyrenees (LTER Aigüestortes site, NE Spain). Modelled back trajectories and precipitation chemistry were used to identify air masses origins. Consistent seasonal patterns were observed in the airborne microbial aeroplankton assemblages with highly diverged summer and winter communities recurrent in time. Indicative microbial taxa were identified mostly for summer and winter air masses as a forensic signature, as well as ubiquitous taxa that would therefore commonly inhabit the atmosphere. Source-tracking analyses for bacteria showed freshwater, cropland and urban biomes as the most important origins in summer, while marine and forest biomes prevailed in winter, in agreement with the reconstruction of the air masses retrotrajectories. Overall, we concluded that the composition of airborne atmospheric microbes is mostly driven by the origin of aerosols, which is subjected to the general air masses regime in the Mediterranean area. From the great consistency of our long-term analysis, we suggested a similar pattern is acting globally in accordance with the recurrent movement of air masses traveling around the world.