Isolation of yeast Saccharomyces cerevisiae from unusual natural habitats

Baker yeast Saccharomyces cerevisiae has been an eukarontic experimental organism since 1960s, becoming even more significant with the determination of its complete nucleotide genome sequence in 1996. Even though its biochemical function in the fermentation process had long remained unclear, its metabolism and products (eg. bread, beer, wine) have been used for millennia. S. cerevisiae yeast represents an important organism for production of recombinant proteins (gene manipulation). Moreover, it exhibits great potential for biofuels and the process of bioethanol production from waste materials such as lignocellulose. The yeast is generally found in anthropogenic environments, yet little is known about its ecology. The purpose of this given thesis was to perform a selective isolation of the S. cerevisiae species from both anthropogenic and less common natural habitats. The aim was to aquire strains with metabolic properties that would be potentially uncommon for the species, yet effective in bioethanol synthesis. In the scope of the research, 273 collected samples were divided into 27 different groups. Through the use of a selective growth medium with the addition of 10 % ethanol, 122 yeast cultures were isolated and initially defined according to their morphology (colour, shape) and micromorphology (cell size and shape). In order to identify the strains according to their homothallic or heterothallic properties, the presence of sexual structures (asci, ascospores) was examined on acetate agar. The concluding identification took place at the molecular genetic level through the comparison of nucleotide sequencing of the regions of internal transcribed spacers 1 and 2, including the 5.8S rDNA sequence (ITS rDNA). From the 122 samples, 44 strains of the S. cerevisiae yeast were isolated. The S. cerevisiae species was typically isolated from vinicultural samples and industrial environment waters, whereas individual strains were isolated also from dairy products, freshly squeezed non-pasteurized juices, the ground beneath fruit trees, fresh or rotten fruits and vegetables, insects, vinegar, decomposed wood, and from silage. The S. cerevisiae strains were determined according to their assimilation, fermentation and temperature profiles, and the differences among individual strains were examined