Occurrence and Distribution of Actinomycetes in Marine Environs and their Antagonistic Activity against Bacteria that is Pathogenic to Shrimps

The mean population density of actinomycetes in water samples from eight stations off Little Andaman Island in India ranged from 0.29 x 103 CFU/ml at station 2 (Naval Area) to 0.45 x 103 CFU/ml at station 4 (Chandra Nallah). Density in sediment samples ranged from 1.21 x 103 CFU/g at station 2 (Naval area) to 3.29 x 103 CFU/g at station 6 (Buttler Bay). Forty-one strains were isolated and tested for their antagonistic activity against Vibrio alginolytics, V. harveyi, and V. parahaemolyticus, bacteria that are highly pathogenic to shrimps. Over 60% of the strains (26) exhibited varying degrees of antagonistic activity. Among them, six showed good activity and were tentatively identified as Streptomyces xantholiticus, S. aureofasciclus, S. galtieri, S. vastus, S. galbus, and S. rimosus. Results suggest that actinomycetes from the marine environment can be used as bio-control agents in shrimp culture systems to control diseases caused by bacterial pathogens. Introduction Disease control has become a major problem in shrimp culture systems as bacterial pathogens have become more and more resistant to conventional therapeutic drugs used by the industry. Shrimp farmers are suffering heavy financial losses and there is a need to find novel bioactive compounds with therapeutic potential that can be used to combat disease. In this respect, actinomycetes, which are known to produce potent antibiotics, deserve to be studied. Compared to terrestrial species, actinomycetes from marine environs are important sources of novel antibiotics (Okami, 1986). Actinomycetes from marine and coastal ecosystems may provide a rich gene pool containing isolates capable of producing useful metabolites (Goodfellow and Haynes, 1984; Okami, 1986). Few attempts have been made to isolate marine actinomycetes (Balagurunathan, 1992; Balaguruna* Corresponding author. E-mail: [email protected]