Phylogenetic analysis and antimicrobial activities of Streptomyces isolates from mangrove sediment

The phylogeny of members of Streptomyces bacteria isolated from mangrove sediments in the Manakudi estuary near the Arabian Sea, India, was analyzed in the present study. Among the 35 different isolates, five organisms, JS-9, JS-11, JS-12, JS-13 and JS-20, exhibited potent antimicrobial effects against methicillin-resistant Staphylococcus aureus (clinical isolate) and methicillin-susceptible S. aureus MTCC 3160 and Salmonella typhi MTCC 733; all other isolates displayed intermediate antimicrobial effects. RFLP analysis of HaeIII and BstUI double-digested 16S rRNA gene fragments of the isolates were distinguished into 20 distinct RFLP types, with the genetic similarity coefficient varying from 0.57 to 0.97. On average, 17 RFLP markers were observed from approximately 50 to 350 bp size and all the RFLP types showed significant genetic polymorphism by clustering into three major clusters. Phylogenetic analysis showed that the 20-member Streptomyces isolates were divided into three major clusters and they shared 97.2-99.8% sequence identity to the 16S rRNA gene sequences of the Streptomyces taxons of marine origin. The distribution of the isolates revealed that the distinct Streptomyces groups were clustered in the phylogenetic tree and there was a good correlation between the diversity of the antimicrobial phenotype and that of the 16S rRNA gene.