A total of 94 marine actinobacterial isolates were found to be associated with 4 sponges: Callyspongia diffusa, Mycale mytilorum, Tedania anhelans, and Dysidea fragilis. Among the cultures 7 strains showed antagonism against fish and shellfish sh pathogens. | S. DHARMARAJ Turk J Biol 35 (2011) 303-311 © TÜBİTAK doi: Antagonistic potential of marine Actinobacteria against fish and shellfish pathogens Selvakumar DHARMARAJ Department of Aquatic Biology and Fisheries, University of Kerala, Kariavattom campus, Trivandrum 695 581, Kerala - INDIA Received: Abstract: A total of 94 marine actinobacterial isolates were found to be associated with 4 sponges: Callyspongia diffusa, Mycale mytilorum, Tedania anhelans, and Dysidea fragilis. Among the cultures 7 strains showed antagonism against fish and shellfish pathogens. Analysis of morphological, physiological, biochemical, and protein profile characteristics suggested that the actinobacterial strains belonged to the genus Streptomyces. The initial screening of the isolates by the spot inoculation method exhibited antibacterial activity against Aeromonas hydrophila. In vitro screening of the submerged culture extracts showed positive inhibition against the fish and shellfish pathogens Aeromonas hydrophila, Serratia sp., and Vibrio spp. The screening of bioactive compounds by UV spectrum confirmed the production of polyene substances, which resulted in absorbance peaks ranging from 225 to 245 nm. In TLC analysis the Rf values ranged from to . The results indicate that the Streptomyces strains isolated from marine sponges produce potential bioactive compounds against fish and shellfish pathogens. Key words: Marine sponges, Actinobacteria, Streptomyces, bioactive compounds, fish and shellfish pathogens Introduction Marine microorganisms are of considerable interest as a new and promising source of biologically active compounds (1). They produce a variety of metabolites, some of which can be used for drug development (2). Marine Actinobacteria is a very important group of bacteria that has considerable value as a prolific producer of antibiotics and other therapeutic compounds. Actinobacteria produce over half of the bioactive compounds in .
