Isolation and characterization of antagonistic Streptomyces spp. from marine sediments along the southwest coast of India

Antagonistic Streptomyces spp. were isolated from marine and mangrove sediment samples collected off Cochin, along the southwest coast of India. Sediment samples were pre-treated and following the soil dilution technique, samples were surface plated on starch casein agar and actinomycetes isolation agar. In the primary screening, 7.4% of presumptive actinomycetes (135 isolates) showed antibacterial activity against one or more bacterial fish pathogens and 3.7% of these cultures showed broad spectrum activity against the tested pathogens. Morphologically white powdery colonies with chalky white /grey appearance were selected as presumptive Streptomyces cultures. Isolates subjected to biochemical, physiological and 16S rDNA characters revealed the presence of three species of Streptomyces dominated by Streptomyces tanashiensis followed by S. viridobrunneus and S. bacillaris. Isolates characterized by 16S rDNA indicated the presence of 650 bp band in Streptomyces spp. Primary screening for activity against selected fish pathogens was done by a cross streak method using modified nutrient agar medium. Prominent isolates showing high zone of activity against the fish pathogens ranged 17-35 mm by the paper disc method. Enriched broth of selected isolates showing high antagonistic activity was screened for pharmacologically active agents revealed ethyl acetate fractions to be active against selected microbial pathogens