Seasonal variability of bacteria in fine and coarse urban air particulate matter
The current knowledge about the microbial communities associated with airborne particulate matter, particularly in urban areas, is limited. This study aims to fill this gap by describing the microbial community associated with coarse (PM10) and fine (PM2.5) particulate matter using pyrosequencing. Particulate matter was sampled on Teflon filters over 3 months in summer and 3 months in winter in Milan (Italy), and the hypervariable V3 region of the gene 16S rRNA amplified from the DNA extracted from the filters. The results showed large seasonal variations in the microbial communities, with plant-associated bacteria dominating in summer and spore-forming bacteria in winter. Bacterial communities from PM10 and PM2.5 were also found to differ from each other by season. In all samples, a high species richness, comparable with that of soils, but a low evenness was found. The results suggest that not only can the sources of the particulate influence the presence of specific bacterial groups but also that environmental factors and stresses can shape the bacterial community.
KeywordsParticulate matter Airborne bacteria
We thank Ezio Bolzacchini and colleagues for PM sampling and Giuseppe Merlino for helping set up the methods. The authors are grateful to Christopher Quince for precious help on the de-noising process and to J. Bunge and L. Woodard for kindly providing the CatchAll beta.4 software and for assistance in calculations. This work was supported by CARIPLO FOUNDATION (Milan, Italy) in the frame of the project TOSCA (Toxicity of particulate matter and molecular markers of risk).
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