Antibacterial activity of 1-methyl ester-nigericin from Streptomyces hygroscopicus BRM10; an endophyte in Alpinia galanga

Strain BRM10 was isolated from the root tissues of Alpinia galanga Swartz. and identified as Streptomyces hygroscopicus BRM10 on the basis of morphology, chemotaxonomy and 16SrDNA sequencing. It was an antagonist of some bacteria, Staphylococcus aureus ATCC25932, Bacillus cereus ATCC6633, Escherichia coli ATCC10536 and Pseudomonas aeruginosa ATCC27853. The culture filtrate and the crude extract from S. hygroscopicus BRM10 were all inhibitory to tested bacteria. The major active ingredients from the crude extract were purified by silica gel column chromatography, thin-layer chromatography and identified to be 1-methyl ester-nigericin (compound 1) and nigericin (compound 2) by NMR and mass spectral data, respectively. Bioassay studies showed that compound 1 had antibacterial activity against Gram positive bacteria lower than compound 2, and its minimum inhibitory concentrations against Staphylococcus aureus ATCC25932 and Bacillus cereus ATCC6633 were 0.5 A mu g/ml and 1.0 A mu g/ml, respectively and no inhibitory activity was observed against Escherichia coli ATCC10536 and Pseudomonas aeruginosa ATCC27853, at a concentration of 64 A mu g/ml.