Abstract:
In the course of identification and screening of antimicrobial activity of 127 actinomycetes were isolated from 98 soil samples collected from Chiangrai, Nan, Phatthalung, Satun, Songkhla, Chaiyaphum, and Trat provinces. On the primary screening, most of these strains showed the antimicrobial activities against Staphylococcus aureus ATCC 6538, Bacillus subtilis ATCC 6633 and Micrococcus luteus ATCC 9341, while few strains showed activities against Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 27853 and Candida albicans ATCC 10231. Enghteen selected strains which showed good antimicrobial activity belong to Streptomyces (Group I), Amycolatopsis (Group II), and Kitasatospora (Group III) based on their phenotypic and chemotaxonomic characteristics including phylogenetic analysis using 16S rDNA sequences. The percentage of 16S rDNA sequence similarity revealed that S72-10 and S76-1 should be identified as Streptomyces termitum (99.6 and 99.8%, respectively), S49-1 as S. aureoversilis (99.4%), S1-2 and S75-5 as S. hygroscopicus (99.8%), S38-2 as S. aureofaciens (99.4%), S33-3 as S. xanthocidicus (99.8%), S55-4 as S. roseocinereus (99.9%), S71-1 as S. mycarofaciens (99.4%), S75-3 as S. albospinus (99.4%), S3-1 and SB12-1 as S. spectabilis (99.6 and 99.7%, respectively). S39-7 was closely related to Amycolatopsis albidoflavus (99.2%). SB7-3 was closely related to A. keratinophila (99.3%). KC19-1, KC20-1, and K57-1 were closely related to A. kentuckyensis (99.3, 98.1 and 99.2%, respectively). SB3-2 was closely related to Kitasatospora putterlickiae (98.9%). Streptomyces and Kitasatospora strains contained MK-9 (H6) and MK-9 (H8), whereas Amycolatopsis contained MK-9 (H4) as major menaquinones. The DNA G+C contents of the strains ranged from 66 to 76 mol%. Streptomyces, Amycolatopsis, and Kitasatospora strains contained LL-diaminopimelic acid, meso-DAP in cell wall, respectively. On secondary screening, S. spectabilis S3-1 was selected for secondary metabolite fermentation. 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 CH2CI2) was active against S. aureus ATCC 6538, methicillin resistant S. aureus 266, 269, 643, B. subtilis ATCC 6633, M. luteus ATCC 9341 and Ps. aeruginosa ATCC 27853.
