Diversity and Distribution of Aspergillus fumigatus and Its Related Species in Izu and Ogasawara Islands, Japan

The taxon Aspergillus section Fumigati comprises several causative agents of aspergillosis. Here, the distribution of Aspergillus sect. Fumigati in outdoor environments of Izu and Ogasawara Islands was investigated. Different strains were isolated from soil samples collected from 68 sites on 9 islands (Izu-oshima, Toshima, Shikinejima, Kozushima, Miyakejima, Hachijojima, Mukojima, Chichijima, and Hahajima), including different landscapes, and identified using morphological characteristics and calmodulin (CaM) sequences. Seven Aspergillus sect. Fumigati species were identified. The occurrence frequency of Aspergillus fumigatus was higher in forest sites on the islands, except for Ogasawara Islands, whereas that of species other than A. fumigatus was higher in bare land and grassland sites on all islands. The occurrence frequency of A. fumigatus was more than 50% on islands between Izu-oshima and Toshima, decreased on islands between Shikinejima and Hachijojima, and was zero on Ogasawara Islands. Considering other Aspergillus species, Aspergillus felis showed high occurrence frequency on islands between Izu-oshima and Shikinejima, Aspergillus pseudoviridinutans on islands between Kozushima and Hachijojima, and Aspergillus udagawae on Ogasawara Islands. At two study sites (grassland and forest sites), the soil was sampled throughout the year to evaluate whether the occurrence frequency of each fungal species was affected by sampling season. At the grassland site, A. pseudoviridinutans was isolated at more than 90% frequency, regardless of the sampling season. A. fumigatus occurrence frequency at the forest site ranged from 0% to 60% and greatly varied among sampling seasons. Thus, differences in island location and landscape affected the distribution of Aspergillus sect. Fumigati.