Identification and Characterization of a Bacteriocin Produced by an Isolated Bacillus sp SW1-1 that Exhibits Antibacterial Activity against Fish Pathogens

The selected isolate, Bacillus sp. SW1-1 showed antibacterial activity against both Gram-positive and Gram-negative bacteria involved in fish diseases, including Edwardsiella tarda, Streptococcus iniae, S. parauberis, Vibrio anguillarum, and V harveyi. The Maximum bacteriocin production was observed at 30 degrees C after 24 h with brain heart infusion medium (pH 7.0). The bacteriocin SW1-1 was purified by 50% ammonium sulfate precipitation, followed by Hi Prep diethylaminoethyl 16/10 FF and Sephacryl S-100 High resolution column chromatography. The substance was characterized as a bacteriocin-like inhibitory substance with a molecular mass of 38 kDa. Bacteriocin SW1-1 was sensitive to the proteolytic action of pepsin, trypsin, chymotrypsin, and protease types I and XIV, and relatively heat labile, despite the fact that bacteriocin activity was still detected after heating at 100 degrees C for 30 min. The activity of bacteriocin SW1-1 was stable in the pH range of 2.0-11.0, and relatively unaffected by organic chemicals. The bacteriocin SW1-1 had a bacteriolytic mechanism, resulting in cell wall degradation of E. tarda. These characteristics indicate that this bacteriocin may be a potential candidate for alternative agent to control important pathogens of fish diseases in aquaculture.