A new strategy to increase the hybridization rate between wine strains of Torulaspora delbrueckii

Genetic improvement through hybridization offers a promising approach to enhance the biotechnological properties of non-conventional yeasts such as Torulaspora delbrueckii (Td), which typically exhibit lower fermentation efficiency compared to the conventional yeast Saccharomyces cerevisiae. Previous attempts to hybridize different Td strains have shown that mixing spores or vegetative cells is not an effective method.

We developed a novel strategy based on recent insights into the Td life cycle. Vegetative cells were mixed in a sporulation medium to induce their need for conjugation just before entering meiosis, which marks the onset of the sporulation process. The killer phenotype and resistance to cycloheximide were used as genetic markers to identify the resulting hybrids.

The frequency of new Td strains exhibiting both phenotypes varied depending on the parental strain pair and the specific experiment, but was consistently above 10⁻³. The hybrid yeasts that demonstrated the greatest stability with respect to the genetic markers were selected for wine fermentation trials.

This method enables the combination of specific traits from two different strains into a single hybrid yeast. Moreover, it provides a means to generate genetic variability, facilitating the selection of new yeasts with improved fermentation efficiency compared to parental strains.