Biochemical characterisation of bacteriocins and genetic determinants of bacteriocin production were investigated in three bacteriocin producer strains, L. lactis subsp. lactis PLL19, PLL23 and PLL47. Industrially important traits such as lactic acid production, proteolytic activity and phage resistance were also investigated in these strains. Bacteriocins of PLL19, PLL23 and PLL47 were characterised as lactostrepcin 2, lacticin 481 and lacticin FS92, respectively, according to their sensitivities to enzyme, pH and heat treatment. SDS-PAGE analysis showed the molecular weights of partially purified lactostrepcin 2, lacticin 481 and lacticin FS92 to be 12,000 Da, 3,400 Da and 3,500 Da, respectively. Bacteriocin production and lactose fermentation ability of these strains were found to be encoded on 27.3 kb, 19.0 kb and 19.6 kb plasmids for PLL19, PLL23 and PLL47 strains, respectively. Plasmids encoding bacteriocin production in PLL19, PLL23 and PLL47 could be transferred by conjugation with the frequency rates of 2.6x10(-3)-4.5x10(-4) per donor cell. The stability of plasmids encoding bacteriocin production ranged from 88% to 92% in conjugants. Lactic acid production (in RSM at 30 degrees C for 6 h) and proteolysis (in RSM at 30 degrees C for 24 h) by these strains (PLL19, PLL23 and PLL47) were 0.48-0.52% and 42.6-61.3 mg Tyr/mL, respectively. None of the strains studied was resistant to all the bacteriophages used in this study.