Antagonism and mechanism of Bacillus subtilis BA015 against Streptococcus agalactiae
LU Xiaocen, DU Mingyang, ZHOU Weijia, MA Hongli, HUANG Luxi, YU Jieying,LIU Jiannan, GUO Sicong, ZHAO Xiaoran, YE Shigen*
Key Laboratory of Mariculture & Stock Enhancement in North China’s Sea, Ministry of Agriculture and Rural Affairs, Key Laboratory of Marine Animal Disease Prevention and Control， Dalian Ocean University, Dalian 116023, China
Abstract: To find new means of treatment of Streptococcusagalactiae disease of aquatic animals, 19 strains with antagonistic effects on S.agalactiae were obtained from 21 strains of Bacillus by double-layer flat plan. Further, BA015 with strong inhibitory effect on S.agalactiae was found by agar plate diffusion method, and identified as a member of Bacillussubtilis by physiological, and biochemical characteristics and 16S rDNA gene sequence. It was found that the cell free supernatant(CFS) of BA015 had the maximal antibacterial diameter(22.8 mm±1.9 mm) after purification with using ammonium sulfate at 80% saturation. The antagonistic fractions of BA015 exposed to ninhydrin reaction showed red in color and were insensitive to high temperature, acid, acid-base, protease, organic solvent and ultraviolet radiation in the active fractions, which was consistent with the characteristics of lipopeptides. The minimum inhibitory concentration (MIC) of the antibacterial component purified by gel column chromatography was 3.2 μg/mL. The MALDI-TOF-MS analysis showed that B.subtilis BA015 produced lipopeptides containing Iturin, Bacillomycin, Surfactin, and Fengycin. In summary, both BA015 and its CFS had potential application value in the prevention and treatment of S.agalactiae in fish.
2021, Vol. 36 
