Sources of Bacteria in Outdoor Air across Cities in the Midwestern United States

Abstract

Bacteria are abundant in the atmosphere, where they often represent a major portion of the organic aerosols. Potential pathogens of plants and livestock are commonly dispersed through the atmosphere, and airborne bacteria can have important effects on human health as pathogens or triggers of allergic asthma and seasonal allergies. Despite their importance, the diversity and biogeography of airborne microorganisms remain poorly understood. We used high-throughput pyrosequencing to analyze bacterial communities present in the aerosol fraction containing fine particulate matter of <2.5 m from 96 near-surface atmospheric samples collected from cities throughout the midwestern United States and found that the communities are surprisingly diverse and strongly affected by the season. We also directly compared the airborne communities to those found in hundreds of samples representing potential source environments. We show that, in addition to the more predictable sources (soils and leaf surfaces), fecal material, most likely dog feces, often represents an unexpected source of bacteria in the atmosphere at more urbanized locations during the winter. Airborne bacteria are clearly an important, but understudied, component of air quality that needs to be better integrated into efforts to measure and model pollutants in the atmosphere.Scientists have long known that bacteria are ubiquitous in the atmosphere. Bacterial concentrations typically range from 10 4 to 10 6 cells m Ϫ3 (28), though concentrations may be far higher in proximity to point sources such as compost facilities, feedlots, and wastewater treatment facilities (1,24,41). Recent evidence suggests that, even in some relatively unpolluted locations, bacteria or portions of bacteria may represent a major component of the organic aerosols residing in the atmosphere (22,44). Airborne bacteria can have important effects on human health and the productivity of managed and natural ecosystems. For example, bacteria can cause allergic asthma and seasonal allergies, diseases which are increasingly prevalent in developed nations (14, 35), with allergic asthma currently affecting millions of people in the United States (2). Likewise, important plant and livestock pathogens are dispersed through the atmosphere (20, 38) and there is some evidence that bacteria are capable of influencing atmospheric processes by initiating cloud condensation and ice nucleation events, potentially altering precipitation patterns (10, 34). Despite their abundance and likely importance, we have a limited understanding of the quantities and types of bacteria found in the atmosphere (45). With recent advances in high-throughput sequencing, we can now describe the dynamics of airborne bacterial populations (5, 7) and determine likely sources of bacteria in the atmosphere (6), building a more comprehensive understanding of those bacteria found in the atmosphere and the control of their populations.With the present study, we describe bacterial abundances and community composition in the near-surface a...

Microbiome of the upper troposphere: Species composition and prevalence, effects of tropical storms, and atmospheric implications

“…It is also reasonable to hypothesize that different bacterial species show different CCN/IN efficiencies and, thus, at high altitudes, we have preferentially sampled species that are not as efficient CCN/IN; i.e., they are less affected by wet scavenging at lower altitudes. Consistent with this hypothesis, we found that Gammaproteobacteria, the most efficient IN bacteria known, did not make up a proportionally large part of the tropospheric communities (SI Appendix, Table S3) compared with the near-surface communities studied previously (9,11,12). Furthermore, model simulations have shown that CCN-active microorganisms have a shorter residence time in the atmosphere than those that are CCN-inactive (29).…”

“…For example, substantially fewer OTUs were found in this study compared with samples collected at 3.2 km at the top of Colorado mountains (9), indicating that not all microbial cells can apparently reach or survive highaltitude conditions. Furthermore, contrary to previous surveys of near-surface atmospheric samples (9,11,12), Gammaproteobacteria did not make up a proportionally large part of the tropospheric communities sampled. These findings might reflect the influence of atmospheric processes and transport of the bacterial cells because several members of Gammaproteobacteria, for example, are known to be CCN-and IN-active.…”

“…These studies have revealed considerably more diverse bacterial and fungal communities to be present in the atmosphere of several ecosystems such as the Amazon River and urban cities compared with what was previously anticipated on the basis of the results of culture-based efforts (9)(10)(11)(12)(13)(14). Furthermore, microorganisms commonly found in soil (15) and vegetation (16), including plant pathogens with IN activity such as Pseudomonas syringae, were frequently observed in the previous culture-independent surveys.…”

Bacteria in drinking water sources of a First Nation reserve in Canada

“…The presence of viable Bacteroidetes (15.8%) in buckets/drums (Fig 3) is also an indication of soil (dust) contamination as Bacteroidetes originating from leaf surfaces, soil and animal fecal matter sources are present in near-surface atmospheric particulate matter (Bowers et al, 2011).…”

Local and regional influences over soil microbial metacommunities in the Transantarctic Mountains

“…Taxa that dominate the total bacterial community may represent groups that become entrained in the atmosphere (Morris et al 2008, Bowers et al 2011) and redistributed over broad scales. While the near-ground aeolian redistribution of cyanobacteria has been documented in the Dry Valleys (Wood et al 2008, Michaud et al 2012, cyanobacteria appear to be a minor component in more broadly dispersed bioaerosols (Bottos et al 2013).…”