Phylogenetically diverse endozoic fungi in the South China Sea sponges and their potential in synthesizing bioactive natural products suggested by PKS gene and cytotoxic activity analysis

Abstract

Sponges are well documented to harbor large amounts of microbes. Though it is known that sponge-derived fungi are important sources for marine natural products, the phylogenetic diversity and biological function of sponge-associated fungi remain largely unknown. In this study, the diversity of culturable endozoic fungi in sponges from the South China Sea was revealed based on the ITS phylogenetic analysis. Meanwhile the fungal potential for producing bioactive natural products was estimated according to the detection of Beta-ketosynthase in the polyketide synthase (PKS) gene cluster and cytotoxic activity bioassay. As a result, diverse fungi including 14 genera (Aspergillus, Penicillium, Scolecobasidium, Eurotium, Alternaria, Fusarium, Hypocreales, Yarrowia, Candida, Hypoxylon, Sporidiobolus, Schizophyllum, Bjerkandera, and Trichosporon) in ten orders (Xylariales, Moniliales, Pleosporales, Saccharomycetales, Hypocreales, Eurotiales, Sporidiobolales, Agaricales, Aphyllophorales and Tremellales) of phyla Ascomycota and Basidiomycota were isolated with Aspergillus as the predominant component in the culturable fungal community. Particularly, genera Schizophyllum, Sporidiobolus, and Bjerkandera in phylum Basidiomycota and genus Yarrowia in phylum Ascomycota were isolated from marine sponges for the first time. PKS genes were detected in 12 isolates suggesting their potential for synthesizing PKS compounds. Among the 12 isolates with PKS genes, 9 isolates displayed strong in vitro cytotoxic activity (e.g. IC50 < 50 μg/ml) against human cancer cell lines A-549, Bel-7402, A-375 and MRC-5. This study demonstrates the phylogenetically diverse endozoic fungi in South China Sea sponges, and highlights the potential of sponge-associated fungi in producing biologically active natural products.