Seasonal changes dominate long-term variability of the urban air microbiome across space and time

Compared to soil or aquatic ecosystems, the atmosphere is still an underexplored environment for microbial diversity. In this study, we surveyed the composition, variability and sources of microbes (bacteria and fungi) in the near surface atmosphere of a highly populated area, spanning similar to 4,000 Km(2) around the city center of Madrid (Spain), in different seasonal periods along two years. We found a core of abundant bacterial genera robust across space and time, most of soil origin, while fungi were more sensitive to environmental conditions. Microbial communities showed clear seasonal patterns driven by variability of environmental factors, mainly temperature and accumulated rain, while local sources played a minor role. We also identified taxa in both groups characteristic of seasonal periods, but not of specific sampling sites or plant coverage. The present study suggests that the near surface atmosphere of urban environments contains an ecosystem stable across relatively large spatial and temporal scales, with a rather homogenous composition, modulated by climatic variations. As such, it contributes to our understanding of the long-term changes associated to the human exposome in the air of highly populated areas.

Automated summary

Compared to soil or aquatic ecosystems, the atmosphere remains relatively unexplored in terms of microbial diversity. This study surveyed microbes in the near surface atmosphere of a highly populated area around Madrid, finding a stable ecosystem with a core of abundant bacterial genera across space and time, modulated by climatic variations. The microbial communities exhibited clear seasonal patterns driven by environmental factors, contributing to our understanding of long-term changes in human exposure in highly populated urban areas.