Isolation, Screening, and Active Metabolites Identification of Anti- Fungal Strains Derived From the Beibu Gulf Coral.

The Beibu Gulf harbors abundant underexplored marine microbial resources, which are rich in diversified secondary metabolites. The genera is a well-known pathogenic bacterium of aquatic animals. In this study, 22 fungal strains were isolated and identified from the Beibu Gulf coral the serial dilution method and internal transcribed spacer (ITS) sequence analysis, which were further divided into three branches by phylogenetic tree analysis. The crude extracts of them small-scale fermentation were selected for the screening of inhibitory activity against , , , , , and . The results showed that eight fungal extracts displayed anti- activity the filter paper disk assay. Several of them showed strong inhibitory effects. Then, two tetramic acid alkaloids, equisetin () and 5'-epiequisetin (), were identified from BBG10 by bioassay-guided isolation, both of which inhibited the growth of spp. with the MIC values of 86-132 μg/ml. The scanning electron microscope results showed that cell membranes of became corrugated, distorted or ruptured after treatment with and . Taken together, this study provided eight fungal isolates with anti- potentials, and two alkaloid-type antibiotics were found with anti- effects from the bioactive strain BBG10. Our findings highlight the importance of exploring promising microbes from the Beibu Gulf for the identification of anti- for future antibiotic development.