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Antimicrobial Activity of Culture Filtrate of Bacillus amyloliquefaciens RC-2 Isolated from Mulberry Leaves

First and second authors: National Institute of Agro-Environmental Sciences, 3-1-1 Kan-nondai, Tsukuba, Ibaraki 305-8604, Japan; third author: Yokohama Plant Protection Service, 5-57 Nakaku, Kitanakadori, Yokohama 231-0003, Japan; fourth author: Tohoku National Industrial Research Institute, 4-2-1 Nigatake, Miyagino-ku, Sendai 983-8551, Japan; fifth author: National Institute of Sericultural and Entomological Science, 1-2 Owashi, Tsukuba, Ibaraki 305-8634, Japan

A potential antagonist, Bacillus amyloliquefaciens strain RC-2, against Colletotrichum dematium, mulberry anthracnose fungus, was obtained from healthy mulberry leaves by in vitro and in vivo screening techniques. Application of culture filtrate of RC-2 inhibited disease on mulberry leaves, indicating that suppression was due to antifungal compounds in the filtrate. Development of mulberry anthracnose on mulberry leaves was inhibited only when the culture filtrate was applied before fungal inoculation, and it was not inhibited by application after inoculation. These results suggest that the antifungal compounds in the filtrate exhibit a preventive effect on the disease. Peptone significantly increased production of the antifungal compounds. The culture filtrate of RC-2 also inhibited the growth of several other phytopathogenic fungi and bacteria, such as Rosellinia necatrix, Pyricularia oryzae, Agrobacterium tumefaciens, and Xanthomonas campestris pv. campestris, in vitro. From the culture filtrate of RC-2, seven kinds of antifungal compounds were isolated by high performance liquid chromatography analysis, and one of the compounds was determined as iturin A2, a cyclic peptide, by nuclear magnetic resonance and fast atom bombardment mass analysis.