Xenorhabdus stockiae PB09 bacterium has been shown to exhibit antifungal activity against several plant pathogens. To improve\nits efficacy, the optimization of the nutritional components in culture media was performed. The medium components that have\nsignificant effects on antifungal activity of X. stockiae PB09 were initially identified using a fractional factorial design. Response\nsurface methodology and central composite design were then used to create a model for optimizing the levels of carbon, nitrogen,\nand mineral sources that maximize antifungal activity of X. stockiae PB09. After that, the suitable carbon, nitrogen, and mineral\nsources were selected and adjusted by the second-order polynomial regression model, which predicted that 98.62% of antifungal\nactivity could be obtained when the medium contained sucrose, yeast extract, NaCl, and K2HPO4 at 3.24, 23.71, 5.46, and 2.73 g/L,\nrespectively. Laboratory verification of this recipe resulted in the antifungal activity at 97.95% in the shake flask experiment after\n48-hour cultivation, which was significantly 27.22% higher than that obtained by using the TSB medium. In addition, X. stockiae\nPB09 cultured in the verified recipe by using 5 L fermenter could effectively inhibit the mycelial growth of Phytophthora sp.,\nRhizoctonia solani, Pythium sp., and Fusarium oxysporum. This study demonstrated that the RSM and CCD were shown to be\nvaluable tools for optimizing the culture medium that maximize the antifungal activity of X. stockiae PB09.
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