Microorganisms are abundant in the near surface atmosphere and make up a significant fraction of organic aerosols with implications on both human health and ecosystem services. Furthermore, urban areas are among the fastest growing ecosystems and host large human populations. In the atmosphere, microorganisms provide numerous ecosystem services including ice/cloud nucleation and active transformation of atmospheric chemistry. As largely transient members of the atmosphere, microbes through dry or wet deposition may alter ecosystem function as well as human health. Thus, understanding how landscape composition alters these communities has implications for city-planning and policy. Despite this, surveys of urban airborne microbial diversity are uncommon and little is known about the structure and function of the near surface (~2 meters) atmospheric microbiome at the city-level spatial scale. Another often overlooked sink of atmospheric microorganisms are those of subway systems. Urban subways represent a distinct ecological niche based on high occupant densities, rapid turnover (i.e. fluxes of people entering and exiting the system), and thus are especially relevant to public health. In this study we use continuous mobile monitoring of microbial diversity measured by collection onto quartz fiber filters and high-throughput sequencing across Philadelphia, PA, USA in two air types (outdoor and subway) that an individual living in the city would experience in daily life.
Results/Conclusions
We have found diverse communities that significantly differ by air type in community structure, diversity, source environment, and function. Furthermore, despite 90% of the city being explained by 10 composite land classes, landscape heterogeneity was significantly correlated with the diversity of near surface atmospheric communities as well as richness. Subway system airs were largely composed of human-associated taxa while outdoor airs hosted more environment non-specific and soil exclusive microbes. This study is the first of its kind to address the city wide-atmospheric microbiome as well as define the role land use complexity in a city in structuring their associated communities.