Growth advantage in stationary phase (GASP) in Eukaryotes

Introduction: The Growth Advantage in Stationary Phase (GASP) phenomenon reflects the remarkable versatility of cells to tolerate stressful conditions. This commonly used strategy for microbial survival has been widely observed and established with different strains of bacteria.

In this study, we tested whether the GASP phenomenon exists in eukaryotes. To this end, a strain of Saccharomyces cerevisiae, termed Sc404 had been isolated from a prolonged period in stressful environment, in the form of a two-year old bottled beer, containing 5% ethanol. This isolated strain was studied and compared to its parental strain Safale in various parameters related to GASP.

Methods: The growth of Sc404 strain was compared to its parental strain, Safale, both in optimal and sub-optimal conditions, and competition experiments of the two strains were performed. In addition, the tolerance of these two strains to stressful environments, including heat, high osmotic pressure, acidity and ethanol was compared. Accordingly, a full genome sequence of both strains was determined and compared.

Results: Indeed, Sc404 presented a significant advantage in survival and growth under the tested stressful conditions over the parental strain, including large amounts of ethanol (20%), basic environment (pH=10) and at high osmotic pressure. Interestingly, in optimal conditions both strains showed similar growth rates. Serial dilutions and growth assays demonstrate that the difference between the strains is irreversible, and therefore genetic in origin. Genomic sequence analysis of the two strains shows dramatic changes in Sc404 which apparently lost about 10% of it genome. Importantly, main stress sensing molecular machineries in the cell are heavily mutated.

Discussion: Our data thus reveal that the remarkable GASP phenomenon is indeed present in S. cerevisiae, showing improvement in survival under various stresses. Moreover, these results suggest that GASP is a general phenomenon which might play a role in the evolution of various kingdoms.