Osmotic stress response of lactic acid bacteria Lactococcus lactis and Lactobacillus plantarum

In order to survive in a wide variety of environments, bacteria have evolve d systems that protect themselves against environmental stress. Lactic acid bacteria grow in media where osmolarity is high and varies frequently and they must adjust their intracellular osmolarity in order to maintain the tu rgor pressure necessary for cell elongation. An osmotic upshock stops their growth and activates specific mechanisms which prevent cells death. The re gulatory mechanisms of the response of Lactococcus lactis and Lactobacillus plantarum to an osmotic stress have drawn increasing attention in recent y ears, because of their use in industrial fermentations and their fundamenta l interest as Gram positive bacteria. The main response to osmotic stress i s the accumulation in the cytoplasm of osmoprotectant organic compounds, th e so-called "compatible solutes", which can accumulate to very high levels without deleterious effects on the cellular metabolism. In this review, we present the state of the art on the physiological and molecular responses o f L. lactis and L. plantarum to an osmotic stress.