Species Diversity and Distribution of Non-fumigatus Aspergillus Species in Ogasawara Islands, Japan.

Aspergillus sections Flavi, Nigri, and Terrei are known as common causative agents of aspergillosis, followed by section Fumigati. A previous study investigated the distribution of section Fumigati in Izu and Ogasawara Islands and found that the dominant species changes depending on the soil environment. This study investigated the species diversity and distribution of sections Flavi, Nigri, and Terrei in Mukojima, Hahajima, and Chichijima of Ogasawara Islands and clarified whether the dominant species vary depending on the soil environment, as in section Fumigati. The strains were isolated from soil samples collected in 2019 and 2020 at 18 sites in three islands, including different landscapes, and species identification was based on the nucleotide sequence of the calmodulin gene. Overall, 172 strains were isolated from all sites and identified to seven section Flavi, five section Nigri, and three section Terrei species. Three section Flavi, three section Nigri, and one section Terrei species have been reported as causative agents of aspergillosis. Three sections were distributed in Chichijima and Hahajima, but only section Nigri was found in Mukojima. The frequency of occurrence of Aspergillus tamarii and Aspergillus nomiae belonging to section Flavi and Aspergillus niger and Aspergillus tubingensis belonging to section Nigri were > 60% in forests, including shrub forests, whereas that of Aspergillus floccosus belonging to section Terrei was > 40% in bare land and grassland. Aspergillus pseudonomiae belonging to section Flavi was isolated at > 40% frequency of occurrence regardless of the landscape. Thus, differences of soil environments affected the distribution of the dominant species belonging to three sections.