Bioassay-guided fractionation and identification of active substances from the fungus Aspergillus tubingensis against Vibrio anguillarum

The aim of this study was to perform bioassay-guided fractionation and identification of active substances against the aquatic pathogen Vibrio anguillarum from the fungus Aspergillus tubingensis SZX-6 associated with the crab Portunus trituberculatus. Based on the antibacterial activity against V. anguillarum, three compounds were isolated and purified from the culture broth of strain SZX-6 by sequential column chromatography over silica gel, Sephadex LH-20 and RP-18. The isolated compounds were identified on the basis of extensive spectroscopic data analysis. They were methyl 6-acetyl-5,7,8-trihydroxy-4-methoxy-2-naphthoate (1), daidzein (2) and genistein (3). Compound 1 showed moderate antibacterial activity against V. anguillarum (minimum inhibitory concentration 0.063 mg/mL). The obtained results could serve as a basis for further research towards design of active antibacterial agents against aquatic pathogens.