Optimization of the Production and Characterization of an Antifungal Protein by Bacillus velezensis Strain NT35 and Its Antifungal Activity against Ilyonectria robusta Causing Ginseng Rusty Root Rot

A biocontrol Bacillus velezensis strain, NT35, was isolated from the rhizosphere soil of ginseng, and its sterile filtrate obtained through a 0.22 μm filter which had significant inhibitory effect against Ilyonectria robusta, causes rusty root rot in Panax ginseng. In order to obtain best filtrate, medium fermentation conditions strain NT35 were optimized using response surface methodology (RSM), composition obtained. Therefore, composed yeast extract powder 2.5%, cornmeal 1.5%, K2HPO4 (NH4)2SO4 2.5%. The optimal inoculum amount 6%, at an initial pH value 7.0 culturing 34 °C 180 rpm. antifungal protein 1-4-2F precipitation via 30% precipitation, desalting by Sephadex G-25, ion-exchange chromatography, gel filtration chromatography. Tricine-SDS-PAGE showed that purified relative molecular weight approximately 6.5 kDa. relatively stable better activity 4–10 20–100 under ultraviolet irradiation 30 W. amino acid sequence mass spectrometry, 100% similarity hypothetical B. YAU B9601-Y2 (Accession No: AFJ62117). Its 10.176 kDa, isoelectric point 9.08, coverage reached 49%. EC50 I. robusta 1.519 μg·mL−1. mycelia morphology changed significantly after treatment with microscopic observation; branches increased, distorted, partially swelled into spherical or elliptical shape, even ruptured; cells became vacuoles.