FLO gene-dependent phenotypes in industrial wine yeast strains

Abstract

Most commercial yeast strains are nonflocculent. However, controlled flocculation phenotypes could provide significant benefits to many fermentation-based industries. In nonflocculent laboratory strains, it has been demonstrated that it is possible to adjust flocculation and adhesion phenotypes to desired specifications by altering expression of the otherwise silent but dominant flocculation (FLO) genes. However, FLO genes are characterized by high allele heterogeneity and are subjected to epigenetic regulation. Extrapolation of data obtained in laboratory strains to industrial strains may therefore not always be applicable. Here, we assess the adhesion phenotypes that are associated with the expression of a chromosomal copy of the FLO1, FLO5, or FLO11 open reading frame in two nonflocculent commercial wine yeast strains, BM45 and VIN13. The chromosomal promoters of these genes were replaced with stationary phase-inducible promoters of the HSP30 and ADH2 genes. Under standard laboratory and wine making conditions, the strategy resulted in expected and stable expression patterns of these genes in both strains. However, the specific impact of the expression of individual FLO genes showed significant differences between the two wine strains and with corresponding phenotypes in laboratory strains. The data suggest that optimization of the flocculation pattern of individual commercial strains will have to be based on a strain-by-strain approach.

Flocculation in ale brewing strains of Saccharomyces cerevisiae: re-evaluation of the role of cell surface charge and hydrophobicity

“…However, the aggregates are calcium independent and are not inhibited by the presence of sugars (glucose, mannose, maltose or sucrose); these facts suggest a cell-cell interaction mechanism different than those observed in the brewing yeast cells. On the other hand, Bayly et al (2005) reported Ca dependence and mannose inhibition of Flo11p-dependent flocculation, while other authors did not observe a flocculent phenotype in strains overexpressing FLO11 gene (Verstrepen and Klis 2006;Govender et al 2008;Mulders et al 2009;Govender et al 2010). These data are consistent with our possibility: although the presence of Flop on yeast cell wall seems to be important on the determination of the percentage of cell hydrophobicity, the degree of yeast flocculation is not related with the level of hydrophobicity.…”

“…In the present work, it was shown that brewing and constitutively flocculent strains displayed a similar flocculation degree (>97%) and a different percentage of hydrophobicity; the brewing strains were ∼2.5-3 times more hydrophobic than the strain S646-1B. On the other hand, CSH alone seems not to be sufficient to provide calcium-dependent and sugar-sensitive flocculation because strains expressing FLO11 presented a high CSH but did not yield a flocculent phenotype (Mulders et al 2009;Govender et al 2010).…”

“…An increase of yeast surface hydrophobicity when the glycoproteins Flo1p, Flo5p, Flo9p and Flo10p are present in yeast cell walls (Verstrepen et al 2001;Govender et al 2008;Mulders et al 2009;Govender et al 2010) was described. Similarly, the expression of FLO11 also confers hydrophobicity to yeast cells (Guo et al 2000;Reynolds and Fink 2001;Fidalgo et al 2006;Mortensen et al 2007;Govender et al 2008;Mulders et al 2009).…”

Lager Yeast Comes of Age

“…Changes in FLO11, namely, a deletion in the promoter region which enhances the expression of FLO11 and an increase in the number of tandem repeat sequences in the central domain, caused these "flor yeast" cells to float and form buoyant biofilms, particularly in sherry wines (85,86). Regulation of FLO gene expression is remarkably complex and generates the basis for strain-to-strain differences that can cause problems on the industrial scale (87). Several FLO genes, FLO1, FLO5, FLO9, and FLO10, are located at telomeres.…”

“…Inactivation of FLO8 in laboratory strains of S288c (due to a premature stop codon) results in lack of FLO11 expression and flocculation (91). To ensure timely flocculation at the end of fermentation in wine yeast strains, FLO genes were placed under the control of stationary-phase-induced promoters derived from ADH2 or HSP30 (87). Taken together, flocculation is a highly evolvable trait in which specific flocculation properties can be selected via conventional yeast breeding.…”