Analysis of the constitution of the beer yeast genome by PCR, sequencing and subtelomeric sequence hybridization.

Abstract

The lager brewing yeasts, Saccharomyces pastorianus (synonym Saccharomyces carlsbergensis), are allopolyploid, containing parts of two divergent genomes. Saccharomyces cerevisiae contributed to the formation of these hybrids, although the identity of the other species is still unclear. The presence of alleles specific to S. cerevisiae and S. pastorianus was tested for by PCR/RFLP in brewing yeasts of various origins and in members of the Saccharomyces sensu stricto complex. S. cerevisiae-type alleles of two genes, HIS4 and YCL008c, were identified in another brewing yeast, S. pastorianus CBS 1503 (Saccharomyces monacensis), thought to be the source of the other contributor to the lager hybrid. This is consistent with the hybridization of S. cerevisiae subtelomeric sequences X and Y' to the electrophoretic karyotype of this strain. S. pastorianus CBS 1503 (S. monacensis) is therefore probably not an ancestor of S. pastorianus, but a related hybrid. Saccharomyces bayanus, also thought to be one of the contributors to the lager yeast hybrid, is a heterogeneous taxon containing at least two subgroups, one close to the type strain, CBS 380 T , the other close to CBS 395 (Saccharomyces uvarum). The partial sequences of several genes (HIS4, MET10, URA3) were shown to be identical or very similar (over 99 %) in S. pastorianus CBS 1513 (S. carlsbergensis), S. bayanus CBS 380 T and its close derivatives, showing that S. pastorianus and S. bayanus have a common ancestor. A distinction between two subgroups within S. bayanus was made on the basis of sequence analysis : the subgroup represented by S. bayanus CBS 395 (S. uvarum) has 6-8 % sequence divergence within the genes HIS4, MET10 and MET2 from S. bayanus CBS 380 T , indicating that the two S. bayanus subgroups diverged recently. The detection of specific alleles by PCR/RFLP and hybridization with S. cerevisiae subtelomeric sequences X and Y' to electrophoretic karyotypes of brewing yeasts and related species confirmed our findings and revealed substantial heterogeneity in the genome constitution of Czech brewing yeasts used in production.

Molecular genetic study of introgression between Saccharomyces bayanus and S. cerevisiae

“…All four S. pastorianus strains have similar DNA reassociation values with the type culture of S. bayanus (72-78%), but differ significantly in DNA relatedness with the type culture of S. cerevisiae. Strains CBS 1486and CBS 1513show 54% and 57%, respectively, while CBS 1503and CBS 1538 The results of the present study, along with literature data (Andersen et al, 1999;Yamagishi and Ogata, 1999;Joubert et al, 2000;Casaregola et al, 2001), indicate that S. pastorianus strains are hybrids, but having different genetic constitutions. Judging from the nDNA-nDNA reassociation data (Vaughan-Martini and Martini, 1987), the strains CBS 1486, CBS 1503, CBS 1513 and CBS 1538 contain more complete S. bayanus genome and different fractions of the S. cerevisiae genome.…”

“…The evidence for introgression between the biological species S. cerevisiae and S. bayanus was obtained for several S. bayanus strains, which harboured some subtelomeric SUC and Y sequences of S. cerevisiae (Naumov et al, 1992;Nguyen et al, 2000;Casaregola et al, 2001). In order to determine how common this phenomenon is among S. bayanus yeasts, we compare here the distribution of some S. cerevisiae sequences in various S. bayanus var.…”

“…The other studies suggest that the non-S. cerevisiae genome of lager brewing yeast is closely related to that of the type culture of S. bayanus CBS 380 (Vaughan-Martini and Kurtzman, 1985;Fujii et al, 1996;Tamai et al, 1998;Yamagishi and Ogata, 1999;Casaregola et al, 2001). VaughanMartini and Kurtzman (1985) confirmed the hybrid composition of the yeast S. carlsbergensis.…”

“…Judging from the nDNA-nDNA reassociation data (Vaughan-Martini and Martini, 1987), the strains CBS 1486, CBS 1503, CBS 1513 and CBS 1538 contain more complete S. bayanus genome and different fractions of the S. cerevisiae genome. Unlike the S. pastorianus strains isolated from brewing fermentations a century ago, modern lager brewing yeasts contain a complete or almost complete S. cerevisiae genome in addition to the non-S. cerevisiae one (Andersen et al, 1999;Azumi and Goto-Yamamoto, 2001;Casaregola et al, 2001;de Barros Lopes et al, 2002). Proteomic analysis with two-dimensional gel electrophoresis also suggested that the whole S. cerevisiae genome contributes to the genetic constitution of lager brewing yeasts (Joubert et al, 2001).…”

“…bayanus CBS 380, but different in S. bayanus var. uvarum CBS 395 (Casaregola et al, 2001). According to the AFLP analysis (de Barros Lopes et al, 2002), the S. pastorianus produced fingerprints considerably more similar to S. bayanus var.…”