Azalomycin F Complex Is an Antifungal Substance Produced by Streptomyces malaysiensis MJM1968 Isolated from Agricultural Soil

MJM1968, an actinomycete showing potent antifungal activity, was isolated and identified by 16S rDNA sequence analysis as Streptomyces malaysiensis. MJM1968 showed strong antifungal activity on phytopathogenic fungi such as Fusarium oxysporum, Rhizoctonia solani, Cladosporium cladosporioides, Fusarium chlamydosporum, Colletotrichum gloeosporioides KACC 40693, Alternaria mali KACC 40026, and Pestalotia spp. KACC 40501, in vitro. An antifungal compound was isolated from culture filtrate of strain MJM1968 by a series of chromatographic methods. Treatment of agricultural soil with strain MJM1968 mycelia reduced the native fungal population by more than 60% after 14 days. Treatment of soil with 10 mg/mL partially purified extract lowered native fungal density by more than 80% after 14 days. The compound, which exhibited antifungal activity in a broad range of pH and temperature, was identified as azalomycin F complex by H-1 and C-13 NMRs. This is the first report on the isolation of azalomycin F complex from S. malaysiensis, demonstrating a broad-spectrum suppression of fungal pathogens in agricultural soil.