Identification and antimicrobial activity of actinomycetes from soil at Samed Island

In the course of identification and screening of antimicrobial activity of 100 actinomycetes isolates from 35 soil samples collected from shore of Samed Island, Rayong province based on morphological, cultural, physiological and biochemical characteristics, 80 isolates were identified as Streptomyces and 20 isolates were identified as Micromonospora. On primary screening, 55 isolates of Streptomyces sp. and 14 isolates of Micromonospora sp., most of these isolates showed the antimicrobial activities against Staphylococcus aureus ATCC 25923, Bacillus subtilis ATCC 6633, and Candida albicans ATCC 10231, while the activities against Escherichia coli ATCC 25922 and Pseudomonas aeruginosa ATCC 27853 could be observed in few isolates. On secondary screening, the strain PC 4-3 with good antimicrobial activity was selected for secondary metabolite fermentation. This strain contained L-diaminopemelic acid in cell wall. Sequencing of 16S rDNA and phylogenetic analysis of PC 4-3 was similar to the Streptomyces strain NRRL B- 1865. The ethyl acetate extract from fermentation broth of this strain showed antimicrobial activity against S. aureus ATCC 25923, B. subtilis ATCC 6633 and c. albicans ATCC 10231. Antimicrobial assay-guided fractionation of the ethyl acetate extract yielded 2 known ansamycins, including geldanamycin and 17-O- demethylgeldanamycin. The chemical structures of the isolated compounds were elucidated through extensive analyses of UV, IR, MS and NMR spectroscopic data and comparison with the literatures. Geldanamycin exhibited antimicrobial activity against S. aureus ATCC 25923 and C. albicans ATCC 10231