MOLECULAR-DETECTION OF STREPTOMYCIN-PRODUCING STREPTOMYCETES IN BRAZILIAN SOILS

Actinomycetes were isolated from soybean rhizosphere soil collected at two field sites in Brazil, All the isolates were identified as Strept omyces species and were screened for streptomycin production and the p resence of two genes, strA and strB1, known to be involved in streptom ycin biosynthesis in Streptomyces griseus. Antibiotic resistance profi les were determined for 53 isolates from cultivated and uncultivated s ites, and approximately half the strains were streptomycin resistant. Clustering by the unweighted pair group method with averages indicated the presence of two major clusters, with the majority of resistant st rains fi om cultivated sites being placed in cluster 1, Only represent atives from this cluster contained strA. Streptomycetes containing str A and strB1 were phenotypically diverse, and only half could be assign ed to known species. Sequence comparison of 16S rRNA and trpBA (trypto phan synthetase) genes revealed that streptomycin-producing streptomyc etes were phylogenetically diverse, It appeared that a population of s treptomycetes had colonized the rhizosphere and that a proportion of t hese were capable of streptomycin production.