16s rDNA Sequence Analyses and Antimicrobial Activities of Streptomyces Strains from Thai Soilsย

Abstract

16S rDNA sequences and phylogenetic analyses of 12 actinomycete strains from soils were carried out including S1-2 and S3-1 from Chiangrai; SB12-1 and S33-3 from Nan; S38-2 from Phatthalung; S49-1 from Songkhla; S55-4 from Chaiyaphum; and S71-1, S72-10, S75-3, S75-5, and S76-1 from in Trat. The percentage of 16S rDNA sequence similarity revealed that S72-10 and S76-1 were closed to Streptomyces termitum NBRC 13087^T (99.6 and 99.8%, respectively), S49-1 to S. aureoversilis NBRC 13021^T (99.4%), S1-2 and S75-5 to S. hygroscopicus DSM 41599^T (99.8%), S38-2 to S. aureofaciens NBRC 12483^T (99.4%), S33-3 to S. xanthocidicus NBRC 13469^T (99.8%), S55-4 to S. roseocinereus NBRC 13829^T (99.9%), S71-1 to S. mycarofaciens NBRC 13792^T (99.4%), S75-3 to S. albospinus NBRC 13846^T (99.4%), and S3-1 and SB12-1 to S. spectabilis NBRC 13424^T (99.6 and 99.7%), respectively. In addition, their phenotypic and chemotaxonomic characteristics were determined for supporting the identification. In the course of screening for antimicrobial activities, most of them exhibited antimicrobial activities against Staphylococcus aureus ATCC 6538, Bacillus subtilis ATCC 6633, Micrococcus luteus ATCC 9341 but few strains did against Escherichia coli ATCC 25922, Pseudomonas. aeruginosa ATCC 27853 and Candida albicans ATCC 10231. The strain S3-1 was selected for secondary metabolite fermentation in YM broth due to its crude extract showing good antimicrobial activity. The ethyl acetate extract was fractionated by chromatographic method and the fractions were tested for antimicrobial activity by agar disc diffusion and bioautographic methods. The active spot found at Rf value 0.8 (Silica gel TLC, solvent system 15% MeOH in CH₂Cl₂) was active against tested bacteria.