Characterization and improvement of non-conventional saccharomyces yeasts to solve new challenges in the wine industryapplication of omics technologies

Laburpena

Saccharomyces yeasts participate in fermentative processes of value in the food industry, such as the production of wine. The wine industry uses selected yeasts to carry out wine fermentation in a controlled manner and to produce a homogeneous wine. At present, S. cerevisiae is the species within the Saccharomyces genus most widely used in the wine industry as starter, because it is very resistant to ethanol, a toxic compound which is produced during fermentations. Nowadays, as a result of climate change, final wines contain higher alcohol and pH levels and a lower total acidity than expected, which are undesirable characteristics in wine. In the Saccharomyces genus there are other species with enological interest, such as S. kudriavzevii and S. uvarum, and hybrids strains between these strains and S. cerevisiae. These Saccharomyces species are gaining popularity as they produce more aromatic wines, with lower ethanol content and higher glycerol. However, they are less ethanol tolerant than S. cerevisiae strains. Taking into account all of the above, in this thesis we proposed the characterization and improvement of different yeast strains of the Saccharomyces genus with the aim of improving their behavior during the wine fermentation process to obtain a better product: the final wine. We have focused on improving ethanol tolerance, since, as we have mentioned, the presence of a high concentration of alcohol during fermentation processes is a high impact stress factor for yeasts. In addition, we have emphasized on trying to relate the different behavior of yeasts to ethanol with their membrane composition and with the genome and transcriptome response of the yeasts, by using omics technologies. The conclusions obtained during this doctoral thesis are several. On the one hand, it was found that ethanol tolerance is variable among different strains of S. cerevisiae and that it can be correlated with the membrane composition and with the transcriptomic response in the presence of ethanol of each strain. On the other hand, it was determined that it is possible to obtain by hybridization a new yeast strain that improves two parents with different characteristics of interest, in our case, high tolerance to ethanol and good production of aromas, glycerol and tolerance to low temperatures. In turn, a hybrid obtained in this way can be adapted in the presence of high sulfite concentration and increasing ethanol concentrations, which leads to the selection of different genomic characteristics that ultimately provide greater tolerance to these stress factors. Finally, it was determined that the adaptive evolution of different species of the genus Saccharomyces in an ethanol media causes different changes in their genomes and in their membrane fluidity, thus revealing the presence of a great variety of evolutionary mechanisms that can act in the presence of ethanol.