Date of Award

Spring 1-1-2011

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Ecology & Evolutionary Biology

First Advisor

Noah Fierer

Second Advisor

Michael Hannigan

Third Advisor

Rob Knight

Abstract

With this dissertation, I present four culture independent studies examining the spatiotemporal distributions of microbial communities in the near-surface atmosphere. The goals of this dissertation work were to examine the biogeographical patterns that airborne microbes exhibit over a variety of spatiotemporal scales, and to determine the likely sources of bacteria to the near-surface environment. First I explored the short-term (two-week) changes in microbial community structure (bacteria, fungi and pollen) of the near surface atmosphere at the high elevation research site, Storm Peak Laboratory, located in northern Colorado, USA. This study revealed that the nearsurface atmosphere is abundant with microbes, and that the airborne communities are composed of taxa that are typical of cold environments. Additionally, the bacteria identified in the air samples showed high sequence similarity to bacterial lineages possessing the ice nucleating phenotype, suggesting the possibility of bacterial induced cloud formation. Second, I examined the spatial diversity of airborne bacterial communities across the three dominant land-use types of the Colorado Front Range: forests, suburban areas, and agricultural sites. The airborne communities exhibited significant community level shifts across the three land-use types, however the differences could not be attributed to the prevailing meteorological conditions, suggesting that the characteristics of the local terrestrial surfaces have a greater influence on the airborne communities than the prevailing meteorology. Overall, the airborne communities above the three land-use types appeared to be unique to potential source environments, however the taxa driving the land-use patterns were related to those taxa that were indicative of either soils or leaf surfaces. Third, I carried out a seasonal (summer and winter) study of the airborne bacterial communities of the Great Lakes region of the USA. The bacterial communities inhabiting the summertime atmosphere appeared to be similar to those communities from previous datasets. However, the winter samples were highly related to a much more unexpected bacterial source community, the bacterial communities found in animal feces. This study demonstrated how crossenvironment analyses of bacterial communities can be an effective tool for tracking bacteria back to their sources. Fourth, I examined the seasonal variability of airborne bacterial communities at Storm Peak Laboratory. Bacterial abundances and total particle abundances were highly correlated and both exhibited significant seasonal variability over the four surveyed seasons. Bacterial concentrations also made up a significant component of the total atmospheric aerosol. The composition of the airborne communities differed by season, where specific taxonomic groups appeared to be driving the observed seasonal shifts. This work demonstrated that airborne bacterial communities often represent a large fraction of total aerosol particles and the taxonomic structure is likely shaped by seasonal shifts in atmospheric conditions and the corresponding changes in the local terrestrial environments

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