Seasonal changes of airborne bacterial communities over Tokyo and influence of local meteorology

Recent progress in Next Generation Sequencing allows us to explore the diversity of airborne microorganisms across time and space. However, few studies have used consecutive short-period samples to explore correlations between the seasonal variation of the microbiota and meteorology. In order to understand airborne bacterial community dynamics over Tokyo, including fine-scale correlations between airborne microorganisms and meteorological conditions, and the influence of local versus long-range transport of microbes, air samples were continuously taken from a platform at the 458-m level of the Tokyo Skytree (a 634-m-high broadcasting tower in Tokyo) from August 2016 to February 2017. Predicted source regions of airborne particles, from back trajectory analyses, changed abruptly from the Pacific Ocean to the Eurasian Continent in the beginning of October. However, microbial community composition and alpha and beta diversities were not affected by this meteorological regime shift, suggesting that long-range transport from ocean or continent was not the principal determinant controlling the local airborne microbiome. By contrast, local meteorology, especially relative humidity and wind speed, had significant relationships with both alpha diversities and beta diversity. Among four potential local source categories (soil, bay seawater, river, and pond), bay seawater and soil were constant and predominant sources. Statistical analyses suggest humidity is the most influential meteorological factor, most likely because it is correlated with soil moisture and hence negatively correlated with the dispersal of particles from the land surface.