Diversity and Antimicrobial Activity of Endophytic Actinomycetes Isolated from Plant Roots in Thailand

Abstract In this study, 37 endophytic actinomycetes were isolated from roots of 14 plant species obtained in Thailand, where biological diversity is known to be high. The isolates were identified as members of the genera Micromonospora (21 isolates), Streptomyces (14 isolates), Plantactinospora (1 isolate), and Polymorphospora (1 isolate) based on their phenotypic characteristics and the 16S rRNA gene sequence . The most frequent isolates (56.8%) were members of the genus Micromonospora. The antimicrobial activity screening showed that seven Micromonospora isolates and eight Streptomyces isolates were active against Bacillus subtilis ATCC 6633, Kocuria rhizophila ATCC 9341 and Staphylococcus aureus ATCC 6538p. To our knowledge, the isolates showed the difference of antimicrobial activity based on the production media. Moreover, this study suggested Thai plant species to be valuable sources of interesting endophytic actinomycetes producing antimicrobial metabolites.