Anti-Vibrio dibutyl phthalate from marine-derived Streptomyces sp. S073

Marine Streptomyces S073 was previously shown to have strong anti-Vibrio activity, and its antibacterial mechanism was proposed to be associated with siderophore-mediated iron competition and other antagonistic agents. In this study, anti-Vibrio compounds produced by S073 were isolated by bioassay-guided fractionation using column chromatography and HPLC, and the target compound in the most active fraction was identified as dibutyl phthalate (DBP) by various spectroscopic analyses, including EI-MS, ¹H NMR and ¹³C NMR. The DBP-producing capacity of S073 was 2.39 mg/L in ISP1 culture media. Pure DBP was demonstrated to have strong inhibitory activity on Vibiro parahaemolyticus growth with an MIC of 31.25 mg/L. When standard DBP was supplemented into the S073 fermentation broth in a gradient method, an additive inhibitory effect on V. parahaemolyticus was observed, indicating the important role of DBP in driving anti-Vibrio activity in S073 metabolites pool. A synergistic additive effect between DBP and florfenicol was observed in the Vibrio inhibition. These results indicate that, to achieve Vibrio-inhibition, S073 exerted multifaceted strategies, which included DBP-mediated antagonism and siderophore-governed iron competition. The application potential of S073 as an aquaculture probiotic was evaluated, and the safety risks associated with the endocrine disruptor attributes of DBP were discussed.