Growth of Lactococcus lactis strains at low water activity: correlation with the ability to accumulate glycine betaine

Lactococcus lactis strains were divided into two groups based on their ability to grow in the presence of an upper limit of either 2% w/v NaCl (sensitive) or 4% w/v NaCl (tolerant). Growth inhibition of NaCl tolerant strains was substantially relieved by glycine betaine which was accumulated in significant amounts when growing at low water activities (aw). Very little accumulation of glycine betaine occurred during growth of the NaCl sensitive strains. The NaCl tolerant strains had substantial levels of glycine betaine transport activity in vitro, whereas the NaCl sensitive strains had little or no such activity. A low aw sensitive mutant of L. lactis subsp. cremoris MG1363 (NaCl tolerant) was isolated following ISS1 insertional mutagenesis. This mutant was inhibited at an aw of 0.988 produced by addition of 2% w/v NaCl or the equivalent glucose concentration (0.58 M). The mutant did not accumulate glycine betaine when growing at low aw, and did not transport glycine betaine when assayed in vitro.