Antagonism and Action Mechanism of Antifungal Metabolites from Streptomyces rimosus MY02

The genus of Streptomyces, a saprophytic Gram‐positive bacterium, has properties, which make them useful as pharmaceutical and biocontrol agents. A streptomyces strain MY02 from soil samples showed significant antagonism against 14 plant pathogenic fungi including Fusarium oxysporum f. sp. cucumarinum. Antifungal metabolite(s) SN06 from the culture of the strain MY02 were extracted with n‐butanol and purified by silica gel column chromatography. The minimum concentration of SN06 inhibiting any visible fungal growth of F. oxysporum f. sp. cucumarinum is 12.5 μg/ml by twofold serial dilutions method. The mycelia of F. oxysporum f. sp. cucumarinum treated with SN06 were observed under the normal optics microscope. The results showed that some cells of hyphae began to dilate and formed some strings of beads. The cytoplasm oozed out of the cells with the culture time and so most of the cells became empty. The hyphae broke into many segments and then collapsed after 48 h. After inoculated in potato dextrose medium for 48 h, the filtrate of mycelia treated with 1% NaCl containing 12.5 μg/ml SN06 was scanned using ultraviolet spectrophotometer and absorption peak at 260 nm showed that the mycelia cell membrane of F. oxysporum f. sp. cucumarinum was broken and that nucleic acid oozed out of the cell.