Abstract

Airborne microbes are ubiquitous in the atmosphere and play an important role in human health, agriculture, cloud formation, global climate, and atmospheric dynamics. We monitored the bacterial abundance and community composition in outdoor aerosol samples collected at urban and suburban sites in Japan. The aim of this study was to get knowledge of bioaerosol characteristics between various particle matter (PM) fractions or between different locations. Air samples were collected between August and December 2016, at a suburban site in Toyama City and an urban site in Yokohama City, Japan. Coarse particles (suspended particulate matter-PM2.5) and fine particles (PM2.5) were collected using slit-jet air samplers. In addition, we sampled using eight-stage Andersen samplers. PM mass, inorganic ions, organic and elemental carbon, and elements were measured following the Manual for Continuous Monitoring of Air Pollution (the 6th Edition). Airborne bacterial abundance and community structure were determined by 16S rRNA gene-targeted quantitative PCR and amplicon sequencing with Illumina MiSeq, respectively. Air mass backward trajectory was analyzed using the HYSPLIT4 model. Statistical analysis was performed using R software. The PM mass concentration, chemical composition, bacterial abundance and community structure differed between urban and suburban sites and across aerosol size fractions. The bacterial communities were dominated by Actinobacteria, Firmicutes, and Proteobacteria. From the network analysis, both coarse and fine particle samples showed the locality in biotic-abiotic interaction. Interestingly, we observed that Legionella spp., the causal agents of legionellosis and Pontiac fever in human, were mainly detected in >2.1 μm coarse particles. Our findings indicate that a complex set of environmental factors, including changing atmospheric conditions, are related to the composition of bacterial communities in urban and suburban site environments. The results of this study provide a foundation for understanding the interaction mechanisms of environmental factors with bioaerosols and the influence of bioaerosols on human health.