Seasonal Variability in Bacterial and Fungal Diversity of the Near-Surface Atmosphere

Abstract

Bacteria and fungi are ubiquitous throughout the Earth's lower atmosphere where they often represent an important component of atmospheric aerosols with the potential to impact human health and atmospheric dynamics. However, the diversity, composition, and spatiotemporal dynamics of these airborne microbes remain poorly understood. We performed a comprehensive analysis of airborne microbes across two aerosol size fractions at urban and rural sites in the Colorado Front Range over a 14-month period. Coarse (PM10-2.5) and fine (PM2.5) particulate matter samples were collected at weekly intervals with both bacterial and fungal diversity assessed via high-throughput sequencing. The diversity and composition of the airborne communities varied across the sites, between the two size fractions, and over time. Bacteria were the dominant type of bioaerosol in the collected air samples, while fungi and plants (pollen) made up the remainder, with the relative abundances of fungi peaking during the spring and summer months. As bacteria made up the majority of bioaerosol particles, we analyzed the bacterial communities in greater detail using a bacterial-specific 16S rRNA gene sequencing approach. Overall, bacterial taxonomic richness and the relative abundances of specific bacterial taxa exhibited significant patterns of seasonality. Likewise, airborne bacterial communities varied significantly between sites and across aerosol size fractions. Source-tracking analyses indicate that soils and leaves represented important sources of bacteria to the near-surface atmosphere across all locations with cow fecal bacteria also representing an important source of bioaerosols at the more rural sites during early fall and early spring. Together, these data suggest that a complex set of environmental factors, including changes in atmospheric conditions and shifts in the relative importance of available microbial sources, act to control the composition of microbial bioaerosols in rural and urban environments.

The contribution of fungal spores and bacteria to regional and global aerosol number and ice nucleation immersion freezing rates

“…The model reasonably captures (within a factor of 2) observed annual mean number concentrations at some sites (Taiwan, Portugal, Spain and Chile), but overpredicts at other locations (Poland and Singapore). As a mean across all sites, simulated annual mean number concentrations are biased high (normalised mean bias (NMB) with greater number concentrations during the summer as observed (Tong and Lighthart, 2000;Yttri et al, 2011;Bowers et al, 2013). We calculated the simulated contribution of fungal spores and bacteria to total supermicron number concentrations.…”

Environmental filtering affects soil fungal community composition more than dispersal limitation at regional scales

“…Airborne fungal diaspora are often temporally variable (Lin and Li, 2000;Jones and Harrison, 2004;Fierer et al, 2008;Frohlich-Nowoisky et al, 2009;Bowers, 2014). These temporal variations have been attributed to shifts in daily temperature (di Giorgio et al, 1996;Calder on et al, 1997;Lin and Li, 2000;Burch and Levetin, 2002), wind direction (di Giorgio et al, 1996), relative humidity (Calder on et al, 1997; Lin and Li, 2000;Burch and Levetin, 2002) and rainfall (Venables et al, 1997;Burch and Levetin, 2002).…”

Fungi diversity in PM<sub>2. 5</sub> and PM<sub>1</sub> at the summit of Mt. Tai: abundance, size distribution, and seasonal variation

“…11248 C. Xu et al: Fungi Diversity in PM 2.5 and PM 1 at the summit of Mt. Tai ris et al, 2002;Yadav et al, 2004;Bowers et al, 2012Bowers et al, , 2013Cao et al, 2014;Ryan et al, 2009). Despite their importance, the abundance, diversity, and community structure of fungi associated with PM have received limited attention in terms of research.…”