PLASMID-ASSOCIATED BACTERIOCIN PRODUCTION BY A LACTOBACILLUS-SAKE STRAIN

A Lactobacillus sake strain L45 isolated from naturally fermented dry sausage, produced a bacteriocin designated lactocin S. The bacteriocin was moderately heat-stable and its activity was sensitive to proteases. Bacteriocin activity was found in the growth medium during the late exponential phase of growth and was directed against selected strains within the closely related genera Lactobacillus , Leuconostoc and Pediococcus. During propagation in liquid medium, non-bacteriocin-producing bacteria (Bac-) appeared with high frequency. Some isolates had also lost immunity to the bacteriocin (Imm-). Analyses of L45 Bac+ Imm+ isolates revealed two plasmids of about 50 kb (pCIM1) and 34 kb (pCIM2). All of the L45 Bac- Imm- variants had lost pCIM1. Three Bac- Imm+ isolates were found which still contained pCIM1. However, DNA restriction enzyme analyses disclosed differences between pCIM1 in the Bac+ Imm+ and Bac- Imm+ isolates. These experiments strongly suggest that the pCIM1 plasmids are involved in production of the bacteriocin and in immunity to the bacteriocin.