Aneuploidy and ethanol tolerance in Saccharomyces cerevisiae. Saccharomyces cerevisiae

Response to environmental stresses is a key factor for microbial organisms growth. One of the major stresses for yeasts in fermentative environments is ethanol. Saccharomyces cerevisiae is the most ethanol tolerant species in its genus, but intraspecific differences exists in ethanol tolerance. Although much effort was done in the last years to discover evolutionary paths to improve ethanol tolerance, this phenotype is still hardly understood. Here we selected five strains with different ethanol tolerance and used comparative genomics to determine which were the main factors that could explain this phenotypic differences. Surprisingly, the main genomic feature shared only by the highest ethanol tolerant strains was an aneuploidy in chromosome III. Transcriptomic data points out that chromosome III is important for the ethanol stress response, and that aneuploidy can be an advantage to fastly respond to ethanol stress. We found that chromosome III copy number can explain differences in other strains. We show that removing the extra copy of chromosome III in an ethanol tolerant strain, returning it to euploidy, strongly affect ethanol tolerance. Chromosome III aneuploidy appears frequently in ethanol tolerance evolution experiments and here we show that aneuploidy is also used by natural strains to enhance their ethanol tolerance.