Genome analysis and engineering of industrial lager brewing yeasts

Lager beer, also referred to as Pilsner, is the most popular alcoholic beverage in the world, with an annual consumption of almost 200 billion litres per year. To make lager beer, brewer’s wort is fermented with the yeast Saccharomyces pastorianus. This microorganism converts wort sugars into ethanol and contributes key flavour compounds to the beer. S.pastorianus is an interspecific hybrid which likely formed about 500 years ago by spontaneous mating between an ale-brewing S. cerevisiae strain and a wild S. eubayanus contaminant.

The genome of lager brewing yeast is exceptionally complex: not only does it contain chromosomes from the two parental species, but these have also undergone extensive recombination and are present in varying copy numbers, a situation referred to as aneuploidy. The S. eubayanus ancestor was only discovered in 2011, enabling an improved understanding of the complex genomeand convoluted evolutionary ancestry of S.pastorianus. Furthermore, recent advances in whole-genome sequencing technology and in gene editing tools have simplified the genetic accessibility and amenability of Saccharomycesyeast genomes. The aim of this thesis was to leverage these advances to investigate how the genetic complexity of current S.pastorianus strains emerged and how it contributes to industrial lager brewing performance, and to develop new methods for strain improvement of brewing yeasts.