Middle-East Journal of Scientific Research 7 (3): 327-334, 2011 ISSN 1990-9233 © IDOSI Publications, 2011 Corresponding Author: Selvakumar Dharmaraj, Tel: +91 96269 49380, 9/36, Second street, Park Avenue, SP Nagar, Thudiyalur, Coimbatore- 641 034, Tamil Nadu, India. E-mail: biochem_selva@yahoo.com. 327 Antagonistic Potential of Streptomyces Associated with the Gut of Marine Ornamental Fishes M.S. Sheeja, D. Selvakumar and K. Dhevendaran Department of Aquatic Biology and Fisheries, University of Kerala, Kariavattom campus, Trivandrum 695 581, India Abstract: Nearly 87 isolates of Streptomyces were found to be associated with the gut of marine ornamental fishes namely Chaetodon collare (Red tail butterfly) and Archamia fucata (Orange-lined cardinal). Among them, only seven strains showed bioactivity against Vibrio cholerae. The seven strains were characterized by conventional methods and the studies strongly suggested the strains belong to the genus Streptomyces sp. The culture extracts of the seven strains were initially screened for antibacterial activity by spot inoculation method which exhibited more than 10 mm of inhibition zone against Vibrio cholerae. In vitro screening of the submerge culture extracts showed more than 10 to 30 mm of inhibition zone against Vibrio cholerae. The production of bioactive substances from the active extracts was confirmed by UV spectral analysis by the absorbance peaks that ranged from 239 to 326 nm and the TLC (Rf values) ranging from 0.46 to 0.78. The results indicated that Streptomyces strains isolated from gut of marine ornamental fishes produced potential bioactive metabolites against Vibrio cholerae. Key words: Marine ornamental fishes Fish gut extract Marine actinomycetes Streptomyces Bioactive compounds INTRODUCTION has been a fruitful area of research in the past decade. Marine organisms produce many of the actinomycetes from marine samples compared to the pharmaceutically active natural compounds (drugs). The diverse range of actinomycetes isolated from terrestrial practical importance of antibiotics and other secondary environments [3]. metabolites is tremendous. They are widely used in Many marine actinomycetes taxon in ocean human therapy, veterinary field, agriculture, scientific sediments were found to have widespread, persistent research and in countless other areas. Natural product populations in ocean systems and some taxa have no medicines have come from various source materials counterparts in terrestrial environments. It is becoming including terrestrial plants, terrestrial microorganisms, evident that marine habitats are an abundant source of marine organisms and terrestrial vertebrates and actinomycetes for discovering natural products. Many invertebrates [1]. Microbial sources are one among them promising bioactive compounds including antimicrobial, synthesizing antibiotics and other secondary metabolites. antitumour, immunosuppressive agents and enzymes Most characteristic features of secondary metabolites are are being discovered from marine actinomycetes [4]. their incredible array of unique chemical structures, very The antibiotics produced are entirely new and unique frequent occurrence and versatile bioactivities. Various when compared to those from the terrestrial ones. Most of antibiotics were mainly isolated from bacteria of different the actinomycetes particularly Streptomyces from marine species. The search for new bioactive substances has environment were isolated from sediments, seawater, been remarkably successful and approximately two third seaweeds, mangroves, mollusks and invertebrates [5-10]. of naturally occurring antibiotics including many medical In the present study, an attempt was made to isolate importance have been isolated from actinomycetes Streptomyces strains from the gut of marine ornamental and the majority from the genus Streptomyces [2]. fishes and tested for their antagonistic potential against The isolation of actinomycetes from marine environments Vibrio cholerae. However, little is known about the diversity of