Abstract:

This study aims to address the technical challenge of precipitation formation and compromised fermentation stability caused by high concentrations of magnesium sulfate in the fermentation medium of Bacillus amyloliquefaciens. Using Bacillus amyloliquefaciens as the test strain, this study employed an improved medium preparation method, that is, pH adjustment prior to the addition of magnesium sulfate. The growth performance, sporulation capacity, and spore thermostability were evaluated in media containing varying concentrations (1.3, 4.6, 16.6g/L) of magnesium sulfate. Furthermore, the survival rate of the spores following spray drying into a powdered formulation was determined. The results showed that following the optimization of the medium preparation protocol, the formation of magnesium hydroxide precipitation was significantly reduced, shortening the fermentation cycle of Bacillus amyloliquefaciens from 24 h to 21 h and improving batch-to-batch consistency. At a magnesium sulfate concentration of 16.6 g/L, the spores exhibited a survival rate of 98.9% after heat treatment at 90℃ for 20 min. Furthermore, the spore survival rate in the powder obtained after spray drying was as high as 97.1%, which was significantly higher than that of the low-magnesium control group (43.3%). The medium preparation protocol of "adjusting pH prior to magnesium sulfate addition" is operationally simple and ensures system stability. This method effectively enhances the spore thermostability in the fermentation broth and improves their survival rate in the powder obtained after spray drying. Consequently, it provides a viable strategy for the large-scale production of Bacillus species. Subsequent experiments in fermentation tanks and molecular mechanism analysis of stress resistance can be carried out.

Key words: Bacillus amyloliquefaciens, magnesium sulfate, magnesium hydroxide precipitation, medium preparation, spore thermostability, spray drying, spore survival rate