Characterization of a Bacillus velezensis with antibacterial activity and inhibitory effect on common aquatic pathogens

The strain CPA1-1 with better antibacterial ability was isolated and screened from healthy Macrobrachium nipponense by spot inoculation for the first time. It was identified as Bacillus velezensis through morphological, physiological and biochemical characteristics in combination with 16S rRNA and gyrB sequence analysis. The characteristics of growth, antimicrobial spectrum, the carrying of antibiotic-related genes and safety analysis of the strain were also studied. The results showed that the optimal growth temperature of strain CPA1-1 was 25-37 degrees C, and the growth of the strain was slow under 20 degrees C. The optimum pH value was 5-9, and the strain was severely inhibited when the pH was lower than 3 or higher than 11. The strain CPA1-1 could grow at a salinity of 5-60 parts per thousand, and the optimal salinity was 5-20 parts per thousand. CPA1-1 has better antibacterial effects on indicator bacteria, Aeromonas veronii, Plesimonas shigelloides, Aeromonas hydrophila, Vibrio parahaemolyticus, Citrobacter freundii, and the average diameter of the inhibition zones were 31.2 mm, 26.5 mm, 23.3 mm, 21.4 mm and 10.5 mm, respectively. Through PCR amplification, the results showed that B. velezensis CPA1-1 carried genes encoding the biosynthesis of various peptidoglycans, polyketone compounds and antimicrobial proteins, such as srfAA, ituA, fenA, dhbA, bmyA, beaS, and dfnA. Besides, the minimum inhibitory concentration of the fermented liquid of strain CPA1-1 against A. veronii, P. shigelloides, A. hydrophila, V. parahaemolyticus and C. freundii were 10(4) to 10(6) CFU/mL. The results of the safety test showed that the strain CPA1-1 had no adverse effects on M. nipponense, Siniperca chuatsi, Eriocheir sinensis and Procambarus clarkii. The strain CPA1-1 screened in this study has the good antibacterial ability. Therefore, it has the potential application prospects to prevent and control a variety of aquatic animal diseases.