Identification Of Marine Probiotic JG1, And Purification And Characterization Of Its Inhibitory Substance

The increase of productivity in aquaculture has been accompanied by ecological impacts including emergence of a large variety of pathogens resistance and harm to human health. These impacts are in part due to the indiscriminate use of antibiotics. Among the solutions, the probiotics may be the most practical and safe approach. 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. A range of microorganisms have been used so far as probiotics, which include Gram-negative and Gram-positive bacteria, yeast, bacteriophages, and unicellular algae. Recently, more and more research focus on the isolation and application of marine probiotics from the aquiculture environments or aquatic animals. One of the probiotics'mechanisms is to inhibit or kill other microorganisms by antagonistic activity. Based on this, isolation of antagonistic bacteria especially from aquaculture and marine animals to inhibit pathogens is demanded. The antagonistic bacteria can be applied as potential probiotics in aquaculture.Marine probiotic JG1 isolated from the environment of mariculture was tested by agar diffusion assay. Strain JG1 had a wide inhibitory spectrum. It appeared the inhibitory activity against many pathogens—Vibrio and Aeromonas. 10-1 thickness marine bacteria JG1 (6.7×107 cfu/mL) was injected into the test fish Brachydanio rerio. 20 days later, all the fishes were still healthy, so it is suggested that marine bacteria JG1 can be considered as the potential probiotic. By the morphological, physiological and biochemical characteristics and 16SrDNA sequence analysis, strain JG1 was identified as Pseudoalteromonas piscicida.General analysis of the inhibitory substance of strain JG1 was conducted by organic solvent extraction. The results reveals that the main part of the active substance maybe a kind of high molecular weight protein component. Extracellular products (ECP) of Pseudoalteromonas piscicida JG1 was made by covering plates with cellophanes. The optimum incubation condition to obtain ECP with the strongest inhibitory activity was studied, the results was 28℃, 48 h. The collected ECP was partially purified by (NH4)2SO4 precipitate, ultrafiltration and gel filtration of Sephadex G-100. The inhibitory substance was sensitive to thermal and protease K treatment. It suggested that JG1's inhibitory activity was related to a bacteriocin or bacteriocin-like substance. Moreover, the results of ultrafiltration and Native-PAGE indicated the correlation between yellow pigment and inhibitory activity. The inhibitory substance of marine probiotic Pseudoalteromonas piscicida JG1 is presumed to be a pigment-protein complex.