One of the main problems when using local yeast isolates in beer production is their poor utilisation of alternative sugars, which directly affects the efficiency and speed of fermentation. Maltose is usually not consumed efficiently under catabolic repression in the presence of glucose, therefore it often remains unused at the end of the fermentation. The purpose of this master's thesis was to generate mutants resistant to 2-deoxyglucose (2-DOG) with application of directed evolution. 2-DOG is an antimetabolite of glucose that deregulates glycolysis and can indirectly forces yeast cell to activate the utilisation of alternative sugars. The main goal of this work was to abolish catabolic repression with glucose in selected 2-DOG resistant mutants and to improve maltose utilisation in two isolates Saccharomyces cerevisiae and S. paradoxus. In the first part of the thesis, the minimum inhibitory concentration of 2-DOG was determined on a defined medium with maltose. 2-DOG dependant survival curves were determined for both strains after the mutagen exposure. By applying directed evolution with mutagenesis, mutants resistant to 2-DOG and colonies that showed faster growth at higher concentrations of 2-DOG compared to the parent strain were isolated. The consumption of glucose, maltose, and ethanol during the fermentation was evaluated by applying HPLC method. We were able to abolish catabolic repression with glucose in selected mutants of S. cerevisiae, considering that the selected mutant strains utilised maltose and glucose simultaneously, in contrast to the parent strain.
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