Airborne Bacterial Community Structure And The Effect Of Haze Pollution In Winter, Beijing

Frequent particulate matter（PM） pollution events happen in Beijing. Exposure to high PM pollution leads to adverse effects on human health. Many studies have examined PM physio-chemical and optical properties. Biological species, especially bacteira, are also important constituents of airborne particles. However, relatively less is known about the community structure of airborne microorganisms, their variations between clean and polluted days.In this thesis, PM_2.5 and PM₁₀ in Beijing were sampled for three years. Based on PM₁₀ mass concentration, nineteen daily PM₁₀ samples in winter were selected for 16 S rRNA gene sequencing to reveal the characteristics of airborne bacterial community in Beijing. Airborne bacterial community in different particle size(PM_2.5 versus PM₁₀), obtained by different biological detection method（16S rRNA gene sequencing method, metagenomic sequencing method and culture-based method）, and in different locations（Beijing, Milan, NewYork and High altitude（Midwestern of United States）） were compared respectively. Chemical compositions of these PM₁₀ samples were analyzed. Environmental factors during the selected sampling period were also obtained, e.g., temperature and relative humidity. Analysis of Variance（ANOVA） and Canonical Correspondence Analysis（CCA） were applied to examine the influence of PM pollution on airborne bacterial community.At phylum level, 22 bacteria are found in Beijing s PM₁₀ samples. The dominant bacteria are Actinobacteria, Firmicutes and Proteobacteria and so on. At genus level, 856 bacteria are identified, Arthrobacter, Clostridium and Bacillus are the most abundant ones. There is a significant similarity between the airborne bacterial community structure in PM_2.5 and PM₁₀ samples. Among all the functional categories obtained from the metagenomic sequencing, the relative percentage of metabolic functional ones is the highest. Frankia, Paracoccus and Propionibacterium are the most abundant ones in 16 S rRNA gene sequencing results, while Geodermatophilus, Bacillus and Kocuria are predominant in metagenomic sequencing results. Compared to culture-based method, 16 S rRNA gene sequencing identified a wider variety of bacteria. Beijing, Milan, NewYork and High altitude（Midwestern of United States） show different airborne bacterial community characteristics at genus level. ANOVA analysis indicates that airborne bacterial community between clean days and polluted days show significant differences（P<0.05）. O3, temperature, NO2, relative humidity and the SO42- and K+ in particulate matter are the important factors that explain the variation of airborne bacterial community during haze pollution.