Isolation, identification, and bioactive metabolites of coral-derived fungus Aspergillus sp. SCSIO 40435 from the South China Sea

Abstract:

[Objective] To investigate the antimicrobial activity and secondary metabolites from the coral-derived fungus Aspergillus sp. SCSIO 40435. [Methods] The coral-associated fungi were isolated by dilution-plating method. One strain-many compounds (OSMAC) approach was used for the analysis of metabolite diversity, and the antibacterial activities of fungal metabolites were tested via the standard disk diffusion method. The bioactive strain SCSIO 40435 was identified by rDNA ITS sequence analysis. The active metabolites of Aspergillus sp. SCSIO 40435 were isolated and purified from the crude extract by chromatographic methods, and their chemical structures were characterized by HRESIMS, 1D and 2D NMR, and single crystal X-ray diffraction analysis. The antibacterial activities of the isolated compounds were measured by the broth microdilution method. [Results] A total of 19 fungal strains were isolated from corals in the South China Sea. The strain SCSIO 40435 with abundant products and multiple antibacterial activities was screened out and identified as Aspergillus sp. SCSIO 40435. Four p-terphenyl compounds were isolated from the crude extract of Aspergillus sp. SCSIO 40435 and identified as dicandidusin A (1), candidusin A (2), terphenyllin (3), and 4″-deoxyterphenyllin (4), among which compound 1 is a new p-terphenyl homodimer. In addition, the single crystal structure of compound 4 was obtained for the first time. [Conclusion] This study demonstrates that corals from the South China Sea are rich in fungal resources and have the potential to produce novel active secondary metabolites, which are expected to become an important source for drug discovery and development.