Exploiting heterozygosity in industrial yeasts to create new and improved baker's yeasts

Abstract

The main aim of the work was to utilize heterozygosity of industrial yeast strains to construct new baker's yeast strains. Commercial baker's yeast strain ALKO 743, its more ethanol tolerant descendant ALKO 554 selected initially for growth over 300 generations in increasing ethanol concentrations in a glucose medium, and ALKO 3460 from an old domestic sour dough starter were used as starting strains. Isolated meiotic segregants of the strains were characterized genetically for sporulation ability and mating type, and the ploidy was determined physically. Heterozygosity of the segregant strains was estimated by a variety of molecular characterizations and fermentation and growth assays. The results showed wide heterozygosity and that the segregants were clustered into subgroups. This clustering was used for choosing distantly or closely related partners for strain construction crosses. Intrastrain hybrids made with segregants of ALKO 743 showed 16–24% hybrid vigour or heterosis. Interstrain hybrids with segregants of ALKO 743 and ALKO 3460 showed a wide variety of characteristics but also clear heterosis of 27–31% effects as assayed by lean and sugar dough raising. Distiller's yeast ALKO 554 turned out to be a diploid genetic segregant and not just a more ethanol tolerant mutant of the tetraploid parent strain ALKO 743.

Hybridization of <em>Saccharomyces cerevisiae</em> Sourdough Strains with Cryotolerant <em>Saccharomyces bayanus</em> NBRC1948 as a Strategy to Increase Diversity of Strains Available for Lager Beer Fermentation

“…The extent of loss of function in HO gene from natural sourdough strains deserves further investigations in future. Like in other baker's yeasts [72], the MATa idiomorph prevails in meiotic segregants, suggesting two possible explanations. MATa monosporic clones could be more viable than MATα ones or, alternatively, sourdough strains could have a MATa/MATa/MATa/MATα genotype.…”

Hybridization of Saccharomyces cerevisiae Sourdough Strains with Cryotolerant Saccharomyces bayanus NBRC1948 as a Strategy to Increase Diversity of Strains Available for Lager Beer Fermentation

“…The extent of loss of function in HO genes from natural sourdough strains deserves further investigations in future. Like in other baker’s yeasts [ 74 ], the MAT a idiomorph prevails in meiotic segregants, suggesting two possible explanations. MAT a monospore clones could be more viable than MAT α ones or, alternatively, sourdough strains could have a MAT a/ MAT a/ MAT a/ MAT α genotype.…”