In this study, a bacteriocin produced by Lactococcus lactis subsp. lactis PD6.9 was purified, characterized and identified. The bacteriocin was purified to homogeneity from culture supernatant by cation exchange and reversed-phase liquid chromatography, and its molecular weight was determined by mass spectrometry. The presence of the nisin gene was confirmed by polymerase chain reaction (PCR) and DNA sequencing. The gene showed that it was a natural nisin variant, nisin Z, as indicated by substitution of an asparagine residue for histidine at position 27. The purified bacteriocin was biochemically pure, and the molecular weight was approximately 3329.571 Da. The peak of nisin Z production by L. lactis PD6.9 occurred after 5 h of culture during stationary phase. This bacteriocin demonstrated inhibitory activity towards significant foodborne pathogens and Staphylococcus aureus strains isolated from dairy cattle diagnosed with mastitis, it may be useful for future applications.
Key words: Antimicrobials, Lactococcus lactis, bacteriocins, identification, inhibitory activity.
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