Isolation of antagonistic marine bacteria from the surface of the gorgonian corals at Tuticorin, south east coast of India

Abstract

Culturable heterotrophic bacteria present on the surface of two gorgonian corals, Subergorgia suberosa and Junceella juncea were isolated and the number of pigmented and non-pigmented strains was noted. The antagonistic effect of the marine isolates was tested against 8 human pathogens and 7 fish pathogens. It was observed that 82% (289) of the isolated bacterial strains were found to be non-pigmented and 61% (214) were identified as Gram-negative. Only 13% (46) of the isolated bacteria were found to be antagonistic against both human and fish pathogens. 74% (34) of the producer strains were found to be non-pigmented, however, mild antagonistic activity was found to be exhibited also by the pigmented strains. Percentage of Gram-negative strains showing activity was found to be 68% (145). All the indicator strains tested were inhibited by at least 10 of the antagonistic marine bacteria. A higher degree of inhibition was conferred by 3 of the isolates (G₁₁₀, G₁₁₁ and G₁₁₃) with maximum zones of inhibition against Escherichia coli (5.5mm) by the strain G₁₁₃. The strains showing higher degree of inhibition against human pathogens (G₁₁₀, G₁₁₁ and G₁₁₃) showed potent inhibition against the fish pathogens too with maximum inhibition against Proteus mirabilis (5mm) by the strain G₁₁₀. The symbiotic bacteria present on the surfaces of these gorgonian corals may yield novel metabolites.