VARIATION IN THE PRESENCE OF PLASMIDS ASSOCIATED WITH PROTEINASE AND BACTERIOCIN PRODUCTION OF LACTOCOCCUS LACTIS ISOLATED FROM NATURALLY FERMENTED MILK

Lactococcus lactis is a major member of the lactic acid bacteria and it is known to produce bacteriocins and proteinases. A total of 32 L. lactis strains were isolated from naturally fermented raw cattle milk and skimmed milk. Only 4 isolates had correlative proteinase and bacteriocin production abilities with evident zones of inhibition and zones of proteolysis (above 5 mm diameter). L. lactis RCM9 had 3 small sized plasmids (1 kbp, 3.5 kp, and 4.5 kbp). L. lactis RCM 21 also possessed 3 plasmids (6 kbp, 9 kbp, and > 10 kbp), while L. lactis SKM 14 possessed 1 plasmid > 10 kbp and L. lactis RCM 15 possessed no plasmid. A combination of plasmid curing treatments of novobiocin (10 μg/ml), ethidium bromide (40 μg/ml), and incubation at 40 o C resulted in an entire loss of plasmids. Phenotypic assertions on the plasmid related bacteriocinogenicity and proteinase activity of both plasmid cured and uncured isolatesrevealed thatbacteriocin and proteinase production in L. lactis RCM 9 and L. lactis RCM 15 were not plasmid mediated but chromosomal associated. However, plasmids were responsible for similar traits in L. lactis SKM14 and L. lactis RCM 21. This showed the inconsistency in plasmid presence and activity within the strains.