Optimization of fermentation conditions and evaluation of stability of Bacillus kochii

Abstract:

[Background] As common biocontrol bacteria, Bacillus exhibit great potential in the prevention and control of plant diseases. [Objective] In this study, we optimized the fermentation conditions and evaluated the stability of Bacillus kochii DDWB with nematicidal activity, aiming to provide theoretical support for the development and application of the strain. [Methods] With the nematicidal activity of supernatant and the OD₆₀₀ of fermentation broth as indexes, we optimized the culture medium and fermentation parameters of DDWB strain via single factor tests and orthogonal design. Furthermore, we analyzed nematicidal activity about pH, temperature, UV irradiation, heredity, and storage stability of the fermentation broth. [Results] The optimized culture medium for DDWB strain contained 2% sucrose, 1% yeast extract, and 2% potassium chloride. The optimized fermentation conditions were initial pH 8.0, the filling volume of 150 mL/250 mL conical flask), the fermentation time of 48 h, the inoculum volume of 8%, the rotation speed of 160 r/min, and the fermentation temperature of 31 ℃. The fermentation broth was sensitive to acid and alkali, and its nematicidal activity degraded after 4 h of UV irradiation. However, the fermentation broth was not sensitive to temperature, and the genes related to nematicidal activity could be stably inherited. [Conclusion] We optimized the fermentation conditions and evaluated the stability of active substances in the fermentation broth of DDWB strain, aiming to make the strain rapidly propagate and maintain its long-term and stable nematicidal activity against root-node nematodes. The findings laid a foundation for evaluating the field efficacy and biocontrol mechanism of DDWB strain.

Key words:Bacillus kochii;root-knot nematode;fermentation conditions;stability