Tolerance to high osmolality of Lactococcus lactis subsp. lactis and cremoris is related to the activity of a betaine transport system.

Lactococcus lactis strains from the subsp. cremoris are described as more sensitive to osmotic stress than subsp. lactis strains. We examined the relation between osmotic tolerance and the activity of the betaine transporter BusA among 34 strains of L. lactis. The cremoris strains that showed reduced growth at high osmolality failed to accumulate betaine. The nature of the defect was found to vary among cremoris strains: lack of the busA encoding region, absence of synthesis or synthesis of an inactive form of BusA. The results suggest that the selection of strains well fitted to the dairy production lead to the loss of an otherwise efficient adaptation mechanism.