Streptomyces species comprise a major group of industrially important microorganisms whose identity is mostly confirmed by chemotaxonomic procedures, which suffer from a lack of manual intervention in species level delineation. The most accurate method in the identification of microbial species involves a sensitive phylogenetic 16S ribosomal DNA (16S rDNA) analysis of a strain under study. The present work deals with the phylogenetic confirmation of the identity of one of the Streptomyces species isolated from the soil of Annamalainagar, Tamilnadu.

Actinomycetes are gram-positive bacteria with branched filaments. They are virtually unlimited sources of novel compounds with many therapeutic applications. They hold a prominent position due to their diversity and proven ability to produce new compounds.

Significance of phylogenetic studies based on 16S ribosomal DNA (16S rDNA) sequences is increasing in the systematics of bacteria and actinomycetes (Yokota, 1997). With the introduction of molecular procedures, especially in phylogenetic analysis, the actinomycetes systematics have been provided with new and powerful taxonomic tools. This helps to elucidate the phylogenetic relationship among the organisms. Molecular systematics which include both classification and identification, originated in the early nucleic acid hybridization studies, but it has achieved a new status following the introduction of nucleic acid sequencing techniques (O'Donnell et al., 1993). The deep phylogenetic relationships among the living organisms can be deduced from the sequence comparisons of ribosomal DNA molecules (Vandamme et al., 1996).

Sequences of 16S rDNA have provided the actinomycetologists with a phylogenetic tree that allows the investigation of the evolution of actinomycetes and also provides a basis for classification.

Phylogenetic (16S rDNA), Strain of Streptomyces sp. Isolated, Annamalainagar Soil, Phylogenetic, Ribosomal, Chemotaxonomic , Actinomycetes, Phylogenetic analysis, Streptomyces species, Sodium Dodecyl Sulphate, SDS, Basic Local Alignment Search Tool, BLAST.