In this study, actinomycetes were isolated from seawater collected from Daejeong-coast of Jeju Island, to evaluate its antibacterial activity against fish pathogens. About 24 actinomycetes strains were isolated and identified using physiological, biochemical and molecular tools. Light microscopic observation of MK-01 strains hows gray spores bearing darkbrown mycelia colony which produce purple pigment. MK-01strain was found to have extensive antibacterial activity against S. iniae, S. parauberis, V.anguillarum, E. tarda. The optimum culture condition such as temperature, pH and NaCl(%) concentration required pH 6~7, 30℃ and 2% respectively.
The results of biochemical and physiochemical studies revealed that the best carbon source, organic nitrogen source and mineral source for cell growth and antibacterial activity are dextrose, tryptone, and MgSO4·7H2O respectively. Ethyl acetate and Methanol treated fractions of MK-01 culture supernatant were used for the antibacterial assay.
Minimum inhibitory concentration (MIC) of Methanol and Ethyl acetated fractions were about 31.25 ㎍/㎖ 32.5 ㎍/㎖, 1000 ㎍/㎖ in the S. iniae, S. parauberis and V. anguillarum respectively while the minimum bacterial concentration (MBC) were found to be 250 ㎍/㎖, 500 ㎍/㎖, 1000 ㎍/㎖ for S. iniae, S. parauberis and V. anguillarum
Phylogenetic analysis based on 16S rDNA sequences of the strain MK-01 shows the high similarity to Streptomyces carpaticus (97.63%).
DPPH radical scavenging activity of different methnol fraction of MK-01 culture showed 31.25㎍/㎖ for 13%, 62.5㎍/㎖ for 15%,, 125㎍/㎖ for 19%, 250㎍/㎖ for 22%, 500㎍/㎖ for 23% and 1000㎍/㎖ for 29% and Ethyl acetate fraction showed 31.25㎍/㎖ for 9%, 62.5㎍/㎖ for 11%,, 125㎍/㎖ for 19%, 250㎍/㎖ for 20%, 500㎍/㎖ for 21.12% and 1000㎍/㎖ for 26% Hydroxyl radical scavenging activity for methnol fraction showed 31.25㎍/㎖ for 13%, 62.5㎍/㎖ for 16.68%,, 125㎍/㎖ for 23.87%, 250㎍/㎖ for 38.2%, 500㎍/㎖ for 42.9% and 1000㎍/㎖ for 58.8% and for Ethyl acetate fraction showed 31.25㎍/㎖ for 9.32%, 62.5㎍/㎖ for 14.68%,, 125㎍/㎖ for 20.78%, 250㎍/㎖ for 29.2%, 500㎍/㎖ for 39.8% and 1000㎍/㎖ for 49.9%
Dietary effect of MK-01 supernatant on non-specific immune response such as Lysozyme activity and Phagocytic activity of Olive flounder was assessed with 3% of supernatant mixed flounder feed.