Partial characterization of lacticin NK24, a newly identified bacteriocin of Lactococcus lactis NK24 isolated from Jeot-gal

Strain NK24 was isolated from Jeot-gal and identified as a bacteriocin producer, which has bactericidal activity against Leuconostoc mesenteroides KCCM 11324. Strain NK24 was identified tentatively as Lactococcus lactis by the API test. The activity of lacticin NK24, named tentatively as the bacteriocin produced by L. lactis NK24, was detected during the mid-log growth phase, reached a maximum during the early stationary phase, and decreased after the late stationary phase. Lacticin NK24 showed a relatively broad spectrum of activity against non-pathogenic and pathogenic micro-organisms as assessed using the spot-on-lawn method. Its antimicrobial activity on sensitive indicator cells was completely destroyed by protease IX or protease XIV. The inhibitory activities of lacticin NK24 were detected during treatments up to 100°C for 30 min. Lacticin NK24 was very stable over a pH range of 2·0–9·0 and to all organic solvents examined. It demonstrated a typical bactericidal mode of inhibition against L. mesenteroides KCCM 11324. The apparent molecular mass of lacticin NK24 was estimated to be in the region of 3–3·5 kDa, which was determined by the direct detection of bactericidal activity after SDS-PAGE.