Screening of antagonistic bacteria against aquatic pathogenic Vibrio and isolation of their antibacterial substances

In order to explore the optimal fermentation conditions and stability of the antibacterial substances in the supernatant, the plate confrontation method was used to screen antagonistic bacteria with the significant antagonistic effects against Vibrio harveyi, and the salting method with the different ammonium sulfate saturation was performed to extract the crude antibacterial proteins. The results showed that Bacillus velezensis BS2-7 had the most significant antagonistic effects against the aquaculture pathogen Vibrio harveyi GDH11385, the fermentation medium for Bacillus velezensis and fermentation temperature had no significant effects on the antibacterial activity, while the fermentation duration had a significant effect (P<0.05); the supernatant had a wide antibacterial spectrum and showed the antagonistic activity against Vibrio harveyi, Vibrio owensii, Vibrio parahaemolyticus, and Bacillus altitudinis; the temperature, pH, and ultraviolet irradiation had significant effects (P<0.05); when the ammonium sulfate with 10% saturation and 20% saturation were added into the supernatant, the crude proteins separated from the fractions had the antibacterial activity against Vibrio harveyi and Vibrio owensii. Our findings provide the sample support and the theoretical basis for the development of antibacterial protein drugs against Vibrio pathogens.