Isolation and Identification of a Bacillus amyloliquefaciens Strain Against Grape Downy Mildew and Optimization for Its Liquid Fermentation Medium

Abstract

An antagonistic bacterial strain named J12 against the grape downy mildew was isolated from 92 bacteria on grape leaves. Antagonistic strains were isolated by exploiting streak plate method. J12 was identified based on morphology observation, physiological and antibacterial characterizations, 16S rDNA sequence analysis, and the phylogenetic tree. The controlling effect of J12 on grape downy mildew was 78.6 %. The liquid fermentation medium of J12 was optimized with the response surface methodology to improve the number of live bacteria. The results showed that the strain J12 was classified as Bacillus amyloliquefaciens. For its liquid fermentation medium, the optimum carbon source was sucrose, the best nitrogen source was soybean meal, and the best C/N ratio was 3:1. By Plackett–Burman design and response surface methodology, the best culture medium formula is 31.18 g/L sucrose, 10.57 g/L soybean meal, 2.206 g/L K2HPO4, 2.5 g/L yeast, 0.5 g/L MgSO4·7H2O. Theoretic optimum cell number was 90.87 × 108 cfu/mL. The number of bacteria in three parallel experiments was 92.54 × 108 cfu/mL, indicating that the equation fits well to the actual production.