Optimization of culture medium and fermentation parameters of Bacillus velezensis HC-8 antagonistic to Erysiphe lonicerae

【Objective】 To provide a theoretical basis for rapid mass production and executing field biocontrol of Bacillus velezensis HC-8 strain antagonistic to Erysiphe lonicerae, it is necessary to optimize its fermentation media and conditions.【Method】 In this study, the strain HC-8 was used as the material, and the single factor experiment and orthogonal test were employed to optimize the fermentation media and conditions; combined with conidial germination assays and plate confrontation test to analyze the inhibition effect of strain HC-8 on conidial germination of E. lonicerae and antifungal activity of strain HC-8 against Fusarium oxysporum, Phytophthora nicotianae and F. verticillioides under the optimized fermentation conditions.【Result】 The most suitable media for HC-8 strain was yeast saccharose peptone media (YSP); the best media formula was peptone concentration of 5.0 g/L, yeast extract concentration of 25.0 g/L and maltose concentration of 10.0 g/L; and the most suitable culture conditions were the fermentation temperature of 37 ℃, the initial pH of 6.0, the shaking speed of 180 r/min, the inoculation volume of 0.100% (v/v), the liquid medium volume of 20 mL/ 300 mL and the incubation time of 48 h. Moreover, strain HC-8 showed inhibition rates of 83.15% on E. lonicerae conidial germination under the optimized fermentation conditions, significantly higher than of 74.65% before optimization(P<0.05, the same below). Furthermore, strain HC-8 displayed inhibition rates of 60.66%, 59.03% and 65.32% against F. oxysporum, P. nicotianae and F. verticillioides, respectively, under the optimized fermentation conditions, which were significantly higher than of 54.31%, 55.24% and 59.17%, respectively, under the condition of before optimization. 【Conclusion】 The optimized medium and fermentation conditions can effectively increase the fermentation yield and antagonistic activity of strain HC-8 against F. oxysporum, P. nicotianae and F. verticillioides, as well as the inhibition on E. lonicerae conidial germination. The optimized scheme can be used in rapid and mass production of fermented HC-8 bacterial suspension.