Assessment and Potential Application of the Probiotic Strain, Bacillus amyloliquefaciens JFP2, Isolated from Fermented Seafood-Jeotgal in Flounder Paralichthys olivaceus Juveniles

The strain Bacillus amyloliquefaciens JFP2 was isolated from Jeotgal, traditional fermented seafood from Jeju Island, South Korea to assess its probiotic and antibacterial effect against fish pathogens. The isolate JFP2 was identified using scanning electron microscopic analysis and 16S rRNA gene sequence analysis. The isolated strain, B. amyloliquefaciens JFP2 showed a broad spectrum of antibacterial activity against both Gram-positive and Gram-negative fish pathogenic bacteria namely Aeromonas hydrophila, Edwardsiella tarda, Photobacterium damselase sup-sps, Photobacterium phosphoreum, Streptococcous parauberis, S. iniae and Vibrio anguillaram. The bacteriocin JFP2 with a molecular mass of 37 kDa that was purified by ammonium sulphate precipitation followed by carboxymethyl-Sephadex column chromatography, showed antibacterial activity at a range of temperatures, from 4o-45oC and at a range of pH values from 2-12. However, loss of antibacterial activity was observed after treating the bacteriocin with proteolytic enzymes such as pepsin, proteinase K, and trypsin. The mode of antibacterial action shown by the bacteriocin JFP2 was bacteriolytic in nature, resulting in cell wall degradation of A. hydrophila. Dietary inclusion of the isolated JFP2 strain showed improved growth performance in juvenile flounder along with increased disease resistance against Streptococcus iniae. These results indicate that the bacteriocin JFP2 belongs to class IIIa bacteriocin that could be used as a potential alternative antibacterial agent to control pathogenic diseases in aquaculture and seafood industries.