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Short-Term Temporal Variability in Airborne Bacterial and Fungal Populations

Department of Ecology and Evolutionary Biology, University of Colorado, Boulder, Colorado 80309,¹ Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Colorado 80309,² Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309,³ Department of Civil, Environmental, and Architectural Engineering, University of Colorado, Boulder, Colorado 80309,⁴ Broad Institute of Massachusetts Institute of Technology and Harvard University, Cambridge, Massachusetts 02142⁵

Received 30 June 2007/ Accepted 24 October 2007

Airborne microorganisms have been studied for centuries, but the majority of this research has relied on cultivation-dependent surveys that may not capture all of the microbial diversity in the atmosphere. As a result, our understanding of airborne microbial ecology is limited despite the relevance of airborne microbes to human health, various ecosystem functions, and environmental quality. Cultivation-independent surveys of small-subunit rRNA genes were conducted in order to identify the types of airborne bacteria and fungi found at a single site (Boulder, CO) and the temporal variability in the microbial assemblages over an 8-day period. We found that the air samples were dominated by ascomycete fungi of the Hypocreales order and a diverse array of bacteria, including members of the proteobacterial and Cytophaga-Flavobacterium-Bacteroides groups that are commonly found in comparable culture-independent surveys of airborne bacteria. Bacterium/fungus ratios varied by 2 orders of magnitude over the sampling period, and we observed large shifts in the phylogenetic diversity of bacteria present in the air samples collected on different dates, shifts that were not likely to be related to local meteorological conditions. We observed more phylogenetic similarity between bacteria collected from geographically distant sites than between bacteria collected from the same site on different days. These results suggest that outdoor air may harbor similar types of bacteria regardless of location and that the short-term temporal variability in airborne bacterial assemblages can be very large.

Published ahead of print on 2 November 2007.