The industrial strain S. cerevisiae PE-2 is a top-performance fermenting yeast that is responsible for about 60% of the Brazilian ethanol production. In this project three diploid experimental populations of this yeast strain are being routinely challenged by shocks of 2 hours exposure to the solvent ethanol. The protocol started with a challenge of 19% ethanol volume in which about 50% of the cells died. The goal is submit the surviving cells to shocks of increasing alcohol concentrations to challenge the limits of cellular adaptation to the stress. Viability rates are estimated after each ethanol treatment that, together with a periodic assessment of cellular growth rates, will allow us to quantify adaptation of the evolving populations to the stressor. Periodic genomic and transcriptomic sequencing will provide a catalog of nucleotide and gene expression variations arising during the evolutionary process. The adaptive impact of the mutations found during genomic sequencing will be independently studied by transforming key mutated alleles onto the progenitor’s background. Further study of the mutated genes will open a window to understand the changes in the biology of the cell associated with the evolutionary adaptation. The scope of the project is to find out how far adaptation can be stretched in face of an evergrowing environmental challenge and to provide a genomic/transcriptomic catalog of variations underlying that adaptation. In addition, we will test the full potential of evolutionary engineering to generate a yeast strain with very high ethanol tolerance, which is one of the most important traits required for yeast strains used in the bioethanol industry. An in-depth understanding of the evolutionary process by the use of epigenomic methods might be also potentially applied to this project.

People involved: Dr. Jeferson Gross and Dr. Ana Paula Jacobus

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