Autolytic Lactococcus lactis expressing a lactococcal bacteriophage lysin gene

We report the expression of a cloned lysin gene of bacteriophase ØvML3 in dairy starter strains of the species Lactococcus lactis subsp. lactis and L. lactis subsp. cremoris . Lactococcal strains, which are sensitive to lysin, were unaffected by its expression during exponential growth but lysed after reaching stationary phase in GM17 broth at 30°C. Lysis could be prevented by osmotic buffering of the medium with sucrose. When grown in milk to mimic dairy fermentations, L.lactis subsp. cremoris strains which expressed the lysin gene lost viability earlier than control strains even when stored at low temperature. This autolytic phenotype has the potential to be exploited in flavor acceleration strategies during cheese manufacture.