Enhanced flavour profiles through radicicol induced genomic variation in the lager yeasts, Saccharomyces pastorianus

• Published in: Yeast (Chichester, England) England), 2022-10, Vol.39 (10), p.535-547
• Main Authors: Cerda Garcia‐Caro, Roberto, Thompson, Georgia, Zhang, Penghan, Hokamp, Karsten, Roche, Fiona, Carlin, Silvia, Vrhovsek, Urska, Bond, Ursula
• Format: Article
• Language: English
• Subjects: accelerated evolution; Acetic acid; Alcohols; amino acid analogues; Amino acid sequence; Amino acids; Aneuploidy; Cellular stress response; Chromosome rearrangements; Chromosomes; Ehrlich pathway; Esters; Evolution; Fermentation; Flavor compounds; Genetic diversity; Genomes; Genomic analysis; HSP90; Hsp90 protein; Hybrids; Lager; Low temperature; Mutagenesis; Mutants; Phenylalanine; Polyploidy; radicicol; S. pastorianus; Saccharomyces cerevisiae; Saccharomyces pastorianus; Transcriptomes; Tyrosol
• ISSN: 0749-503X; 1097-0061
• DOI: 10.1002/yea.3815

The yeasts, Saccharomyces pastorianus, are hybrids of Saccharomyces cerevisiae and Saccharomyces eubayanus and have acquired traits from the combined parental genomes such as ability to ferment a range of sugars at low temperatures and to produce aromatic flavour compounds, allowing for the production of lager beers with crisp, clean flavours. The polyploid strains are sterile and have reached an evolutionary bottleneck for genetic variation. Here we describe an accelerated evolution approach to obtain lager yeasts with enhanced flavour profiles. As the relative expression of orthologous alleles is a significant contributor to the transcriptome during fermentation, we aimed to induce genetic variation by altering the S. cerevisiae to S. eubayanus chromosome ratio. Aneuploidy was induced through the temporary inhibition of the cell's stress response and strains with increased production of aromatic amino acids via the Shikimate pathway were selected by resistance to amino acid analogues. Genomic changes such as gross chromosomal rearrangements, chromosome loss and chromosome gain were detected in the characterised mutants, as were single‐nucleotide polymorphisms in ARO4, encoding for DAHP synthase, the catalytic enzyme in the first step of the Shikimate pathway. Transcriptome analysis confirmed the upregulation of genes encoding enzymes in the Ehrlich pathway and the concomitant increase in the production of higher alcohols and esters such as 2‐phenylethanol, 2‐phenylethyl acetate, tryptophol, and tyrosol. We propose that the polyploid nature of S. pastorianus genomes is an advantageous trait supporting opportunities for genetic alteration in otherwise sterile strains. In this paper, the authors describe the generation of new strains of the polyploid yeasts, Saccharomyces pastorianus, through stress‐induced changes in chromosome copy number and composition, coupled with selection for increased production of higher alcohols and esters that impart enhanced flavour profiles on lager beers produced through fermentation. Take‐away • Radicicol was used to induce genetic diversity in interspecific Saccharomyces pastorianus hybrids for improved flavour profiles. This drug is known to inhibit the chaperone Hsp90. Amino acid analogues of phenylalanine were used to select strains with improved production of 2‐phenylethanol and 2‐phenylethyl acetate. • Two S. pastorianus mutants were selected based on their overproduction of higher alcohols and esters derived from the