Long-range transported bacterial communities relating to ice nucleation accumulated in snow cover on Mount Tateyama, Central Japan

The westerly wind blowing at high altitudes over East Asia transport aerosols from Asian desert area and anthropogenic area to downwind area such as Japan. The long-range transported aerosols include not only mineral particles but also microbial particles “bioaerosols”, which impact the ice-cloud formation processes as ice nuclei. However, the the detail relations of airborne bacterial dynamics to ice nucleation in high-elevated aerosols have not been investigated. Here, we used the aerosol particles recorded in the snow cover at the altitudes of 2,450 m on Mt. Tateyama, for estimating the sequential changes of airborne bacterial populations relating to ice-nucleation activities in aerosols. After the stratigraphy of the snow layer formed on the walls of a snow pit on Mt. Tateyama, snow samples including aerosol particles were collected from 70 layers at the lower (winter accumulation) and upper (spring accumulation) parts of the snow wall. The aerosols recorded in the lower parts would mainly came from Siberia of Russia North Asia and Japanese Sea, while those of upper parts would increased the Asian-dust particles, which originate from the desert regions and industrial coasts of Asian continent. The snow samples exhibited high activities of ice nucleation in correspondence to the increase of Asian-dust particles. The MiSeq sequencing analysis using 16S rRNA genes revealed that the bacterial compositions in the snow samples predominately included the members of the plant associated and marine bacteria (the phyla Proteobacteria) during winter, whereas changed to the main group of terrestrial bacteria (the phyla Actinobacteria and Firmicutes) during spring, when dust events arrived frequently. The relative abundances of Firmicutes significantly positively related to the ice-nucleation activities of snow samples. Moreover, the isolates of Firmicutes (Bacillus species) showed higher ice nucleation activities than Proteobacteria isolates. Presumably, Asian-dust events change the airborne bacterial communities over Mt. Tateyama and carry the terrestrial bacterial populations, which induce ice-nucleation activities in atmosphere and indirectly effects on climate changes.