Genomic variations in Saccharomyces cerevisiae populations: diffusion in vineyards and effect on vinification processes

The project of this doctoral thesis arisen from a previous work of vineyard yeast isolation, collection and characterization, which was held at the Wine Microbiology laboratory of the University of Padova in Conegliano (CIRVE). Some genomic variations have been uncovered thanks to the genome sequencing of four S. cerevisiae strains. The relationship between the yeast genotype and phenotype is one of the most debated topics in wine microbiology. Aimed to trying deepening the knowledge regarding the genomic variations effects on the oenological performances of wine yeasts, this thesis is focused on the diffusion of some genomic variations in vineyard yeasts populations and on their implications on the strains technological phenotype. The oenological characterization of Brazilian Saccharomyces cerevisiae yeast strains has been performed, paying attention to the link between the local agricultural practices and the strains biodiversity in vineyard. Results showed that the heavy use of Cu in plant protection contributed to develop a strong Cu tolerance in the autochthonous population. This effect didn’t affect the strains genotype biodiversity so those vineyards were confirmed as great reservoir for wine yeast strains isolation and selection. The strains Cu and SO2 tolerance has been studied on Italian and Brazilian S. cerevisiae vineyard strains. The studied topics were the relationship between the CUP1 Copy N° Variation and the Cu tolerance and the relationship between the presence of two chromosomal translocations and the SO2 tolerance. Results evidenced an association between genetic traits and tolerant phenotypes at vineyard population level, in particular for Cu tolerance and the CUP1 CNV. Moreover, hints of an association between Cu and SO2 tolerance are discussed. The fermentable carbon sources uptake in 4 S. cerevisiae strains has been investigated. The expression of the hexose transporters genes has been analysed during stationary phase of synthetic must fermentation. The study involved FSY1, found in EC1118 and encoding for a high affinity fructose/H+ symporter, present in the 25% of the vineyard strains. Gene expression analysis evidenced that strain-specificity is not related to a single gene but it depends on the main regulation pathways. The higher utilization of FSY1 by P301.9 and R31.3 seems counterbalancing their higher glucose preference during fermentation. The FSY1 putative role in wine yeast seems to be its acting as helper of more effective carbon sources utilization at the latest fermentation stages. This work can contribute in improving the wine yeasts characterization by giving a tool for their distinction for fitness in the winemaking environment, at transcriptional level. Lastly, S. cerevisiae strains EC1118 and QA23have been studied under the Martinotti’s method for sparkling wine production. The yeast cells viability during the pied-de-cuve preparation, the pressure evolution in autoclave and the cells response to the wine chilling at the end of the second fermentation were taken into account. During the wine chilling, cells have been recovered for the total RNA extraction to be used in transcriptomic analysis. Preliminary results show that EC1118 has been characterized by lower cells viability than QA23 since the ethanol adaptation procedure and all along the fermentative process. This difference reflected to the pressure evolution kinetic. Data of the total RNA extraction, quantification, integrity and quality check are also presented.