Lager Yeast Design Through Meiotic Segregation of a Saccharomyces cerevisiae × Saccharomyces eubayanus Hybrid.

Kristoffer Krogerus,Jia-Xing Yue,Gianni Liti,Virve Vidgren,Sandra Castillo,Frederico Magalhães,Gopal Peddinti,Matteo De Chiara,Brian Gibson

doi:10.3389/ffunb.2021.733655

Abstract

Yeasts in the lager brewing group are closely related and consequently do not exhibit significant genetic variability. Here, an artificial Saccharomyces cerevisiae × Saccharomyces eubayanus tetraploid interspecies hybrid was created by rare mating, and its ability to sporulate and produce viable gametes was exploited to generate phenotypic diversity. Four spore clones obtained from a single ascus were isolated, and their brewing-relevant phenotypes were assessed. These F1 spore clones were found to differ with respect to fermentation performance under lager brewing conditions (15°C, 15 °Plato), production of volatile aroma compounds, flocculation potential and temperature tolerance. One spore clone, selected for its rapid fermentation and acetate ester production was sporulated to produce an F2 generation, again comprised of four spore clones from a single ascus. Again, phenotypic diversity was introduced. In two of these F2 clones, the fermentation performance was maintained and acetate ester production was improved relative to the F1 parent and the original hybrid strain. Strains also performed well in comparison to a commercial lager yeast strain. Spore clones varied in ploidy and chromosome copy numbers, and faster wort fermentation was observed in strains with a higher ploidy. An F2 spore clone was also subjected to 10 consecutive wort fermentations, and single cells were isolated from the resulting yeast slurry. These isolates also exhibited variable fermentation performance and chromosome copy numbers, highlighting the instability of polyploid interspecific hybrids. These results demonstrate the value of this natural approach to increase the phenotypic diversity of lager brewing yeast strains.

Highlights

Industrial lager yeast are derived from limited genetic stock
Limited phenotypic and genetic diversity exists between industrial lager yeasts (Okuno et al, 2015; Gallone et al, 2019; Langdon et al, 2019)
We sought to explore how sporulation of a newly created tetraploid S. cerevisiae × S. eubayanus interspecies hybrid could be exploited to expand the phenotypic diversity of this group

Summary

Introduction

The Saccharomyces pastorianus yeast strains used for lager beer fermentation are natural interspecies hybrids of S. cerevisiae and S. eubayanus (Liti et al, 2005; Dunn and Sherlock, 2008; Nakao et al, 2009; Libkind et al, 2011; Walther et al, 2014; Gallone et al, 2019; Langdon et al, 2019). Lager strains originally arose after one or possibly two hybridization events that probably occurred when a domesticated strain of S. cerevisiae encountered a contaminant S. eubayanus strain during a traditional ale fermentation (Dunn and Sherlock, 2008; Walther et al, 2014; Baker et al, 2015; Monerawela et al, 2015; Okuno et al, 2015; Gallone et al, 2019; Salazar et al, 2019). Greater functional diversity amongst lager brewing yeast would be of advantage to the brewing industry, as there exists a demand for more efficient resource utilization and an increased trend for variety in beer characteristics (Kellershohn and Russell, 2015)

Methods

Results

Conclusion