Fungal diversity in coral reef sand and separation and identification of the natural products from Cladosporium sp. GXIMD02067

Abstract:

[Background] The fungi in marine sediments are rich in bioactive natural products, while little is known about the fungi in coral reef sand and their natural products. [Objective] To isolate fungi from coral reef sand and separate their natural products, explore the fungal diversity, and lay a foundation for the development of natural products from marine fungi. [Methods] The fungi from coral reef sand were isolated with the dilution-plate method and identified based on the ITS rDNA sequences. The natural products of Cladosporium sp. GXIMD02067 were separated by silica gel column, reversed phase column, and preparative HPLC. The chemical structures of natural products were identified by nuclear magnetic resonance spectroscopy and comparison with literature data. [Results] Nineteen fungal strains belonging to 6 genera, 4 families, 4 orders, and 1 class were isolated, including 7 strains of Aspergillus, 6 strains of Penicillium, 2 strains of Cladosporium, 1 strain of Lecanicillium, 2 strains of Lulworthia, and 1 strain of Parengyodontium. GXIMD02065 and GXIMD02066 shared the ITS rDNA sequence similarity less than 87%, which indicated that they may be new strains. Seven compounds were separated from Cladosporium sp. GXIMD02067 and identified as pyrenocine A (1), pyrenocine B (2), thymidine (3), 1H-indole-3-carbaldehyde (4), p-hydroxybenzoic acid (5), methyl 2-(4-hydroxyphenyl)acetate (6), and p-hydroxybenzaldehyde (7). Compound 1 showed inhibitory activities against Staphylococcus epidermidis, Actinomyces viscosus, and Bacillus subtilis, with the minimal inhibitory concentrations of 62.5, 62.5, and 125μg/mL, respectively, while other compounds were inactive at the test concentrations. Compounds 1–7 demonstrated no inhibitory activities against a-glucosidase. [Conclusion] The paper reported the fungi from coral reef sand and their natural products for the first time, which enriched the knowledge about the diversity of fungi in coral reef sand and their natural products and laid a foundation for further research on such active natural products.