AUTHOR=Huang Bingyao , Peng Shuai , Liu Shifang , Zhang Yanting , Wei Yuxiao , Xu Xinya , Gao Chenghai , Liu Yonghong , Luo Xiaowei 

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

JOURNAL=Frontiers in Microbiology

VOLUME=13

YEAR=2022

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2022.930981

DOI=10.3389/fmicb.2022.930981

ISSN=1664-302X

ABSTRACT=<p>The Beibu Gulf harbors abundant underexplored marine microbial resources, which are rich in diversified secondary metabolites. The genera <italic>Vibrio</italic> is a well-known pathogenic bacterium of aquatic animals. In this study, 22 fungal strains were isolated and identified from the Beibu Gulf coral <italic>via</italic> 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 <italic>via</italic> small-scale fermentation were selected for the screening of inhibitory activity against <italic>Vibrio alginalyticus</italic>, <italic>Vibrio coralliilyticus</italic>, <italic>Vibrio harveyi</italic>, <italic>Vibrio parahaemolyticus</italic>, <italic>Vibrio owensii</italic>, and <italic>Vibrio shilonii</italic>. The results showed that eight fungal extracts displayed anti-<italic>Vibrio</italic> activity <italic>via</italic> the filter paper disk assay. Several of them showed strong inhibitory effects. Then, two tetramic acid alkaloids, equisetin (<bold>1</bold>) and 5′-epiequisetin (<bold>2</bold>), were identified from <italic>Fusarium equiseti</italic> BBG10 by bioassay-guided isolation, both of which inhibited the growth of <italic>Vibrio</italic> spp. with the MIC values of 86–132 μg/ml. The scanning electron microscope results showed that cell membranes of <italic>Vibrio</italic> became corrugated, distorted or ruptured after treatment with <bold>1</bold> and <bold>2</bold>. Taken together, this study provided eight fungal isolates with anti-<italic>Vibrio</italic> potentials, and two alkaloid-type antibiotics were found with anti-<italic>Vibrio</italic> effects from the bioactive strain <italic>F. equiseti</italic> BBG10. Our findings highlight the importance of exploring promising microbes from the Beibu Gulf for the identification of anti-<italic>Vibrio</italic> for future antibiotic development.</p>