Screening and Medium Optimization of Antagonistic Bacillus Against Tobacco Brown Spot Disease

Three strains were selected as the Bacillus agtagonists against tobacco brown spot disease from 93 strains stored in our lab, the strain K₁₁ showed the highest percentage inhibition of radial growth (PIRG). The PIRG was 63.64% by the dual culture while 67.44% in culture filtrate tests. According to the physiological and biochemical characteristics, the strain K₁₁ was identified as Bacillus subtilis. Based on the single factor experiments and orthogonal experiments for K₁₁, an optimum fermentation medium for biomass production in flasks composed of glucose 20.0 g/L, soybean meal 30.0 g/L, K₂HPO₄·3H₂O 1.0 g/L, and MgSO₄·7H₂O 0.1 g/L. Under the optimum fermentation conditions, the highest biomass yield was 1.28×10¹⁰ CFU/mL, which was 6.5 times of the initial KMB medium, and the sporulation rate reached as much as 95%.