Optimization of fermentation medium formula and fermentation conditions for enhancing the inhibitory activity of Bacillus velezensis F-37 against Ralstonia solanacearum by response surface methodology

Abstract:

[Background] The biocontrol bacterium Bacillus velezensis F-37 can effectively inhibit the viability of the pathogenic bacterium Ralstonia solanacearum, which causes ginger bacterial wilt. The response surface methodology (RSM) and quadratic general rotary design can optimize the fermentation medium formula and fermentation conditions of the biocontrol bacterium with a few tests. [Objective] Tooptimize the fermentation medium formula and fermentation conditions of B. velezensis F-37, enhancing its inhibitory activity against R. solanacearum. [Methods] With the antagonism effect as the indicator, single-factor experiments and RSM were employed to optimize the fermentation medium formula for B. velezensis F-37. A quadratic general rotary design was employed to optimize the fermentation conditions. The Oxford cup method was employed to compare the antagonistic activity of sterile filtrates of strain F-37 against R. solanacearum before and after optimization. [Results] Wheat starch, yeast powder, and potassium chloride were the most significant carbon source, nitrogen source, and inorganic salt, respectively, for the antibacterial activity of F-37. The optimal medium formula was composed of 14.9 g/L wheat starch, 8.6 g/L yeast powder, and 7.8 g/L potassium chloride. The best fermentation conditions were inoculum size of 1.0%, 27 ℃, liquid volume of 78 mL/300 mL, pH 7.8, rotation at 180 r/min, and fermentation for 3 days. Under these optimized conditions, the inhibition rate of the sterile filtrate of F-37 against R. solanacearum was 70.10%, significantly higher than that (46.9%) before optimization, representing a 49.5% increase. [Conclusion] The optimized medium and fermentation conditions significantly improved the inhibitory activity of B. velezensis F-37 against R. solanacearum, providing a technical basis for the development and application of biocontrol preparations for ginger bacterial wilt.