Summary: A 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 and 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 BacImm isolates revealed two plasmids of about 50 kb (pCIM1) and 34 kb (pCIM2). All of the L45 BacImm variants had lost pCIM1. Three BacImm isolates were found which still contained pCIM1. However, DNA restriction enzyme analyses disclosed differences between pCIM1 in the BacImm and BacImm isolates. These experiments strongly suggest that the pCIM1 plasmids are involved in production of the bacteriocin and in immunity to the bacteriocin.


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