characterization and screening of antimicrobial activity of micromonospora strains from thai soils

Aims: Rare actinomycete strains were isolated from mountain soils and island soil collected in Thailand. They were screened for antimicrobial activity and characterized for their secondary metabolites.Methodology and results: The strains were isolated by the standard dilution technique using starch casein nitrate agar. They were identified and characterized based on the phenotypic, chemotaxonomic and genotypic characteristics. The chemotaxonomic characteristics of ten isolates coincided with those of the genus Micromonospora. On the basis of phylogenetic analysis using 16S rRNA gene sequences and DNA-DNA relatedness, they were divided into 6 Groups, ASC19-2-1 (Group A) was identified as Micromonospora marina; AL8-8 and AL10-3 (Group B) were M. aurantiaca; AL7-5 (Group C) was M. chalcea; AL3-16 and AL9-20 (Group D) were identified as M. chokoriensis; AL9-13 and AL9-22 (Group E) were M. tulbaghiae; and AL1-15-2 and AL1-16B (Group F) were M. chersina. On the primary screening, only the isolate AL7-5 (Group C) could inhibit Kocuria rhizophila ATCC 9341. This isolate produced rakicidin when cultivated on A3M, A11M and A16 media and produced compound BU4664L only on A16 medium.Conclusion, significance and impact of study: The isolation and characterization of the rare actinomycetes from Thai soils will be useful for the taxonomic study and for the discovery of bioactive metabolites that are active against microorganisms.