Fermentation optimization to improve production of antagonistic metabolites by Bacillus subtilis strain BS501a

To improve antagonistic metabolites production of Bacillus subtilis strain BS501a, physical parameters of fermentation and metal inorganic salts in medium, namely initial pH value, culture temperature, fermentation time, concentrations of CaCl₂, FeSO₄, ZnSO₄, MnSO₄ and MgSO₄, were optimized using one-factor-at-a-time and orthogonal tests. The results show that the optimal physical parameters of fermentation are an initial pH of 7.0, a culture temperature of 30 °C, and a fermentation time of 48 h. The optimal concentrations of metal inorganic salts in basal medium are 10.2 mmol/L CaCl₂, 0.4 mmol/L FeSO₄, 3.5 mmol/L ZnSO₄, 0.6 mmol/L MnSO₄ and 2.0 mmol/L MgSO₄. Among the metal inorganic salts, MgSO₄ and MnSO₄ play important roles in the improvement of the antagonistic metabolites production of B. subtilis strain BS501a; especially, MgSO₄ contributes a highly significant effect. The average diameter of inhibition zone of the BS501a filtered fermentation supernatant (FFS) cultured in the optimal fermentation conditions against Magnaporthe grisea DWBJ329 reaches 71.4 mm, and there is 2.4-fold increase in antifungal activity as compared with 21.2 mm under the pre-optimized conditions.