The aim of the master thesis was to investigate the phenotypic adaptations of genetically diverse clones of S. pastorianus strain WS34/70 isolated from successive beer fermentations. Previous studies have shown that point mutations and structural changes in chromosomes occur during the serial repitchings of yeasts in beer fermentations, resulting in genetically heterogeneous biomass. Based on previous experiments in which researchers obtained morphologically distinct yeast clones from 31-times repitched biomass, we compared the specific growth rates of these clones in barley wort and in media with maltose and maltotriose as the only carbon sources. We found that the clones isolated from for several times re-used biomass had higher specific growth rates compared to the first generation of biomass re-use. We also determined the kinetics and fermentation rate of clones in barley wort by measuring the mass of exhausted CO2, and the ability to convert wort sugars to ethanol by HPLC analysis. The results confirmed the prediction that the clones from several-times repitched biomass fermented wort more efficiently than the parental strain. Nevertheless, the wort fermentation efficiency of the clones from the same serial re-use differed, suggesting that the wort contains a phenotypically heterogeneous yeast population. In the second part of the study, the genome of our S. pastorianus strain WS34/70 belonging to Frohberg lineage was compared with the genome of S. pastorianus strain CBS 1483 using a genome alignment algorithm. From this anaylsis we determineed the coding genome regions lacking in the WS34/70 strain compared to the CBS 1483 strain. Functional annotation revealed that these genes are required for flocculation and resistance to oxidative stress.
|
