Bacillus sp. IS-2가 생산하는 대사산물의 생리활성 및 사료 내 첨가에 따른 양식 넙치의 면역반응과 병저항성에 미치는 영향

Abstract

The purpose of this experiment was to select useful probiotic strains with antibacterial activity and acid resistance against a broad range of bacteria causing fish diseases to prevent bacterial diseases of fishes or improve their immune system for the efficiency of farming industry. Five kinds of strains extracted from Kimchi, salted farmed flatfish, and salted fishes were used to study their antibacterial activity, bile resistance, and acid resistance, and Bacillus sp. IS-2 was finally selected to examine their cultural, morphological, genetic, and physiological characteristics. In result of identification, Bacillus sp. IS-2 was identified as Bacillus subtillis, Bacillus velzensis, and Bacillus amyloliquefaciens and named Bacillus sp. IS-2. In result of reviewing the optimal culturing conditions for maximum production of antibacterial materials, the source of carbon was 1% soluble starch; the source of nitrogen was 0.5% malt extracts and 0.5% NaNO3; the inorganic salt was 0.1% NaCl; the culturing temperature was 35℃; the initial pH of culture medium was 8; and the culturing time was 120 hours. The strains were added to the feed in the concentration of 103, 105, and 107 CFU/kg and 2% of fishes were given the feed twice a day (8 AM and 5 PM) for 12 weeks. In result of the nonspecific immune response study to examine Lysozyme activity, Phagocytosis activity, and respiratory burst every two weeks until the end of the study, all test samples showed greater activities than control samples and improved immune activity with Bacillus sp. IS-2. The mortality test performed by artificial infection using S.iniae, a pathogenic bacterium, after the completion of this study also showed over 55% greater survival rate in all test samples. In result of performing PCR using the universal primer to verify that the probiotic stays in the intestines of the fishes, all test samples showed PCR product of 1465 bp. Based on the above findings, it was concluded that Bacillus sp. IS-2 in the feed improved farmed flatfish's immune system and resistance against diseases as the probiotic. Also, the physiological indicators discovered by this study would be useful for identifying the mechanisms of probiotics.