Phylogenetic diversity and bioactivity of culturable deep-sea-derived fungi from Okinawa Trough

Deep-sea sediments are now recognized as a home for rich and largely microbial community. Recently, it has been believed in an increasing number of studies that bacteria could be abundant in deep-sea sediments of many types; however, fungi in deep-sea sediments remain relatively unknown. The phylogenetic diversity and bioactivity of culturable deep-sea-derived fungi from Okinawa Trough sediments were investigated in traditional method combined with fungal identification of molecular biology in this study. A total of 76 isolates belonged to 15 fungal taxa were recovered in a harsh condition of low nutrient and low temperature, indicating that the fungal communities in deep-sea sediments from Okinawa Trough were relatively abundant and diversified. Aspergillus, Cladosporium, and Penicillium were the dominant fungal genera, while Mycosphaerella, Purpureocillium, and Schizophyllum were relatively rare in the deep-sea sediments from Okinawa Trough. Among the six genera recovered, Mycosphaerella was firstly recovered from deep-sea sediments in this study. Moreover, about 75% of the extracts from the 15 fungal representative isolates displayed distinct bioactivity against at least one indicator bacterium or marine macrofouler, emphasizing the potentials of these deep-sea-derived fungi from Okinawa Trough as producers of bioactive metabolites. Notably, isolates Cladosporium oxysporum SCSIO z001 and Penicillium citrinum SCSIO z049 displayed a wide spectrum of bioactivities, isolates Cladosporium cladosporioides SCSIO z015, Cladosporium sphaerospermum SCSIO z030, and Penicillium verruculosum SCSIO z007 exhibited a strong anti-bacterial-growth activity, and isolate Penicillium chrysogenum SCSIO z062 displayed a strong anti-larval-settlement activity. These results suggest that these isolates deserved further study as potential sources of novel bioactive metabolites.