Improvement of phage defence in Lactococcus lactis by introduction of the plasmid encoded restriction and modification system LlaAI.

Abstract

To study the ability of the plasmid-encoded restriction and modification (R/M) system LlaAI to function as a bacteriophage resistance mechanism in Lactococcus lactis during milk fermentations. Plasmid pAIcat4, carrying the R/M system LlaAI and a chloramphenicol resistance cassette, was introduced into the plasmid-free strain L. lactis MG1614 and the industrial strain L. lactis 964. By measuring changes in conductivity the influence of different phage on the growth was determined. The plasmid-encoded R/M system LlaAI significantly improves the bacteriophage resistance of L. lactis during milk fermentations. It is essential to determine the potential of a phage defence mechanism in L. lactis starter culture strains during growth in milk before steps are taken to improve starter cultures. This study shows that LlaAI is useful for improvement of starter cultures.