The YEASTDOC research programme is now completed with the original research goals successfully achieved. The work has led to the award of six double doctorates already, with six more theses due for submission in the coming months. There have been over forty conference proceedings and seventeen peer-reviewed papers in high quality journals published to date, with other research outcomes in preparation for publication. Several patents have or will be filed and other research outputs are technical know-how that will be applied in industrial research settings.
In a context of yeast-based fermented beverages, nitrogen source, availability and uptake is of utmost importance. Different projects in YEASTDOC focused on the study of nitrogen assimilation and catabolism in Saccharomyces and non-Saccharomyces yeasts from genetic, evolutionary, and biotechnological perspectives.The results allowed describing genotypic and environmental settings that are beneficial for the final aroma of fermented beverages, and the most promising combinations have been tested under industrially relevant conditions with real grape must.
Throughout the food and beverage industries that utilise yeasts in fermentation and production, hybrids are found that exhibit beneficial characteristics of each parental species (or strains within a species). In addition, non-conventional yeasts are less well characterised in terms of sexual reproduction, and most yeasts (conventional and non-conventional) generally have mating type switching mechanisms that make controlled breeding difficult. In YEASTDOC, we successfully screened many isolates of all the extant Saccharomyces species to identify potential partners for new hybrids that have desired traits for brewing. With Zygosaccharomyces yeasts, Z. balii is the main species found in food spoilage, however there are various hybrids used in beverage fermentation including Z. parabailii. Here, we developed tools for physical analysis of chromosome content as well as molecular tools for genetic engineering. Finally, genetic and molecular tools were developed for K. marxianus which until now has been resistant to attempts at crossing and breeding. In the project, several methods of yeast cell factory strain development and improvement were applied. Over the course of the project, the results contributed to significant advances in the capacity to develop different yeast species using engineering strategies such as genome engineering, ALE, reverse engineering, and construction of hybrids. The results show that these methods have now reached an advanced stage of maturity and are highly effective for a range of different yeast species.
In addition to their roles in the production of fermented beverages, yeast have features that make them very useful for cell factories to make commercial products such as bioethanol, organic acids, bioflavours and enzymes. One of the objectives of this project is to develop strains with new traits that can be exploited for the generation of beverages with new properties as well as more robust strains that cope with both substrate and product-induced cellular stress and that have the ability to grow on inexpensive substrates. To this end, we identified genes and alleles that are relevant to the improvement performance of yeast used in fermentation process. First, we identified genes that contribute to the improvement of aroma and flavour of fermented beverages by exploring the metabolism and characteristics of non-conventional yeasts opening possibilities of finding interesting traits with potential industrial applications. Second, we gained insight into molecular mechanisms involved in the robustness and performance of industrial yeasts growing on sustainable substrates like pentoses, glycerol, and succinic acid. Finally, we described genes that contribute to enhance organic acid stress tolerance that represents a major stress in industrial bio-based microbial processes.
