Seasonal variation in airborne microbial communities of the Akiyoshi-do (cave) : Speleothems damaged by phototrophic bioaerosols

The Akiyoshi-do (cave), which possesses various kinds of speleothems, is attracting many tourists as special natural monuments. However, in recent, the low-energy lighting used for speleothem viewing allowed photosynthetic microbial proliferation to change the surface colors of speleothems from yellow to green with reducing the natural-monument worthies. Although photosynthetic microorganisms are expected to disperse throughout cave atmosphere, their dispersion mechanisms in the cave are unclear. In this project, we collected aerosol samples in the Akiyoshi-do to analyze the microbial communities in cave atmosphere. MiSeq amplicon sequencing targeting 16S rRNA genes indicated the members of the phyla Actinobacteria, Firmicutes, and Proteobacteria, which could be originated from the terrestrial, phyllosphere or freshwater environments outside cave, as well as inside cave areas (guano). Cyanobacteria sequences were also randomly detected from the database ranged from 1.0% to 10% suggesting the green-color microorganisms, such as Cyanobacteria, disperse by the ventilation air in cave.