Antifungal activity of 3-methylcarbazoles from Streptomyces sp. LJK109; an endophyte in Alpinia galangal.

ABSTRACT

Strain LJK109 was isolated from the root tissues of Alpinia galanga (L.) Willd. and identified as Streptomyces sp. on the basis of morphology, chemotaxonomy and 16SrDNA sequencing. It was an antagonist of phytopathogenic fungi; Alternaria porri, Colletotrichum gloeosporioides, Colletotrichum musae, Curvularia sp., Drechslera sp., Exserohilum sp., Fusarium oxysporum, Verticillium sp. and Sclerotium rolfsii. The culture filtrate and the crude extract from Streptomyces sp. LJK109 were all inhibitory to tested phytopathogenic fungi. The major active ingredients from the crude extract were purified by silica gel column chromatography, thin-layer chromatography and identified to be 3-methylcarbazole (compound 1) and 1-methoxy-3-methylcarbazole (compound 2) by NMR and mass spectral data, respectively. Bioassay studies showed that compound 1 and 2 had antifungal activities against tested fungi, and its minimum inhibitory concentrations were found to be within the range of 30 to 240 μg/ml. Conidia germination was also inhibited by these compounds as determined by microscopy.