The yeast Saccharomyces cerevisiae is one of model organisms for eukaryotic cells and it often used in industry. It is one of the most widely used organisms and, due to its efficient utilization of carbohydrates in the fermentation process, it has been used in beer production for centuries. The use of recombinant techniques for genetic manipulation of microorganisms is not welcomed in the food industry. Therefore, other strain improvement techniques have to be used. One of them is application of directed evolution with mutagenesis; via selection pressure, we can isolate mutants with improved phenotype which can be beneficial for example in the beer production process. The main goal of this work was to establish and evaluate the methodology of directed evolution in yeast to generate mutants with desired traits. Using UV and EMS mutagenesis and cultivation on YNB medium containing maltose as the sole carbon source and 2-deoxyglucose (2DG) as the selective pressure, we obtained several 2DG-resistant mutants of the industrial strain S. cerevisiae. To evaluate the phenotype of the isolated mutants, we initially carried out fermentation in smaller volume (2 ml). We then selected 12 mutants and evaluated glucose and maltose utilization ability, which was tested in fermentations at a 50 ml scale. The content of glucose, maltose, glycerol and ethanol was measured by HPLC. The amount of glucose and maltose consumed during fermentation was compared to the parent strain. We were able to successfully abolish catabolic repression with glucose in selected mutants, considering that altered succession of sugar utilization was observed compared to the parent strain.
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