Microbial ecologists frequently investigate how human activities directly or indirectly influence microbes living in aquatic and terrestrial systems with such research often applied to the management of soil and water quality. In contrast, microbes are rarely considered in the management of air quality as most of the research and policy-making decisions focus on abiotic components of the atmosphere. Microbiologists have known for many decades that bacteria are abundant in the atmosphere, but most of this work has centered around the small minority of bacteria that are readily cultured. As a result, we currently lack a fundamental understanding of the spatial and temporal patterns exhibited by airborne bacterial populations and the factors that influence these patterns. The persistence of these knowledge gaps is particularly striking considering that airborne bacteria can have important effects on human health by acting as potential allergens or pathogens of animals and plants.
With this talk, I will focus on recent work demonstrating how ecological studies of microbial life in the atmosphere provide new insights into biosphere-atmosphere interactions and how human activities on land directly influence the abundances and composition of bacteria in the air we breathe. We have used high-throughput pyrosequencing to survey the bacterial communities in hundreds of outdoor air samples from across the U.S. as well as those bacterial communities in >500 samples representing potential source environments. Collectively, this work has demonstrated that the atmosphere harbors surprisingly diverse communities that often vary in a predictable manner across space and time. Land-use type was shown to have a strong effect on airborne bacterial communities due to differences in the relative importance of bacterial source environments (namely soils and leaf surfaces). In metropolitan areas, we found some unexpected sources of bacteria to the atmosphere. In particular, dog feces seems to be a dominant source of bacteria to the outdoor air during winter months in certain midwestern U.S. cites. Many unanswered questions remain and we are only just beginning to document the spatiotemporal dynamics of airborne bacterial communities and the relevance of these dynamics to public health.