Antagonistic potential of marine Actinobacteria against fish and shellfish pathogens

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 shellfi sh 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 confi rmed the production of polyene substances, which resulted in absorbance peaks ranging from 225 to 245 nm. In TLC analysis the Rf values ranged from 0.40 to 0.78. The results indicate that the Streptomyces strains isolated from marine sponges produce potential bioactive compounds against fish and shellfish pathogens.