Identification And Inhibitory Activity Of The Extracellular Products Of Marine Bacteria

The research of probiotics for aquatic animals is increasing with the demand for environment-friendly aquaculture. The probiotics were defined as live microbial feed supplements that improve health of aquatic animals, accommodate the balance of gastrointestinal microorganisms of fish and shellfish and increase the resistance to diseases of their host. The research on probiotics used as biocontrol in the field of aquaculture has been becoming the focus in present.Marine bacteria L1 was isolated from healthy larvae of Penaeus monodon, L2 and L3 strain was isolated from microbial biofilms of antiseptic steel pieces. By 16S rDNA sequence analysis and the morphological, physiological and biochemical characteristics, marine bacteria L1 was identified to be Pseudoalteromonas aurantia, L2 was identified to be Pseudoalteromonas piscicida and L3 was identified to be Pseudoalteromonas citrea.The extraction of antibacterial extracellular products (ECP) was conducted by the method cellophane plate technique. The optimum incubation condition to obtain ECP with the strongest antimicrobial activity was studied. The results indicated that the optimum condition was 28℃, 48 h for L1 strain; 22℃, 48 h for L2 strain; and 25℃, 24 h for L3 strain.The extracellular products with antimicrobial activity of P. aurantia strain L1, P. piscicida strain L2 and P. citrea strain L3 was purified by Gel filtration of Sephadex and SDS-PAGE. The characters of inhibitory substances of L1,L2 and L3 strain towards pH,thermal,protease K treatment indicated the antibacterial extracellular production was determined to be protein.