Untangling the complexity of yeast hybrids and flavour production

Abstract

The brewing yeast strains underwent centuries of domestication, being improved for growth and aroma profile through spontaneous mutations and selection. While genetic modifications have achieved promising results, allowing improvements in both fitness and aroma profiles, their application must deal with the stigma and the regulations associated with GMO products. Researchers must also face the complexity of the fermentation process, in term of variable feedstock, lack of reproducibility, and of the industrial strains used, which are hindering the application of predictive quantitative approaches. Indeed, brewing yeasts commonly evolved as sterile hybrids and often present copy number variations, duplications, and aneuploidy. In this thesis, we applied a combination of genomics and metabolomics tools to untangle the genomic complexity of industrial hybrids and of the brewing process itself, revealing new strategies for both strain and process development. First, I studied how growth rate affects the aroma profile of S. cerevisiae type strain (NCYC 505) in chemostat experiments at different dilution rates. The study allowed to identify a correlation between growth and the production of the major volatile compounds, shedding new light on how yeast physiology may drive their production. Moreover, the data generated allowed to design a feeding profile to effectively manipulate aroma compound production through nutrient availability. Second, I applied state-of-the-art techniques to harness the biodiversity of Saccharomyces species and study how hybridisation and natural variation affect traits of industrial interest. I presented a novel platform to study inter-species hybrids by crossing geographically distant strains from different species through rare mating, effectively restoring fertility in hybrid strains and allowing quantitative genetics studies. The pipeline developed allowed to identify species-specific and hybrid-specific features responsible for traits of biotechnological interest for the production of fermented beverages, and for antifungal resistance. Furthermore, it allowed to dissect the complexity of the hybrid genome and to assess the genome-wide effect of mito-nuclear interactions on the QTL landscape. Lastly, I explored the brewing potential of Saccharomyces jurei in lab-scale and pilot-scale fermentations, assessing both the fermentation capabilities and the aroma profile of this recently discovered species. Moreover, through spore-to-spore-mating, novel S. jurei x S. cerevisiae hybrids of great interest for the beverage industry were generated, presenting good fermentation performances and unique aroma profiles. Overall, the combination of approaches and studies presented in this thesis allowed us to help untangle the complexity of the brewing yeast, refine the industrial process, and to highlight the incredible potential of natural strains and novel hybrids in brewing.

Date of Award	1 Aug 2023
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Daniela Delneri (Supervisor) & James Winterburn (Supervisor)