Preservation of microorganisms of interest (ferments, probiotics) in dry form is widespread in the industry. However, the dehydration processes lead to variable survival rates according to the group, species and strain of microorganism considered, but also according to the type of process used (drying, freeze drying, freezing). The plasma membrane (PM), by its position between the intra-and extracellular environment, is a target of hydric perturbations. Changes in this structure during hydric stresses are described to be directly involved in microorganism death. Understanding of membrane responses occurring during a dehydration/rehydration cycle is essential to maximize the survival of microorganisms in the process of dehydration.Manipulations performed in this study aimed to characterize functional (integrity) and structural (deformations, lateral distribution of sterol-rich microdomains) changes of the PM of Saccharomyces cerevisiae during different types of hydric perturbations (osmotic dehydration of different magnitudes and kinetics, drying in different gas atmospheres). The impact of the composition of PM on yeast survival was also studied by using mutants accumulating different types of sterols in membranes. This work confirmed the strong involvement of the PM in cell death during hydric perturbations. The study of membrane changes helped to elucidate the relationship between the kinetics of dehydration and survival of yeasts. It has also been shown that ergosterol is a key molecule for the survival of yeasts during hydric perturbations.
