Novel wine-mediated FLO11 flocculation phenotype of commercial Saccharomyces cerevisiae wine yeast strains with modified FLO gene expression.

Depending on the genetic background of Saccharomyces strains, a wide range of phenotypic adhesion identities can be directly attributed to the FLO11-encoded glycoprotein, which includes asexual flocculation, invasive growth and pseudohyphal formation, flor formation and adhesion to biotic and abiotic surfaces. In a previous study, we reported that HSP30-mediated stationary-phase expression of the native chromosomal FLO11 ORF in two nonflocculent commercial Saccharomyces cerevisiae wine yeast strains, BM45 or VIN13 did not generate a flocculent phenotype under either standard laboratory media or synthetic MS300 must fermentation conditions. In the present study, the BM45- and VIN13-derived HSP30p-FLO11 wine yeast transformants were observed to be exclusively and strongly flocculent under authentic red wine-making conditions, thus suggesting that this specific fermentation environment specifically contributes to the development of a flocculent phenotype, which is insensitive to either glucose or mannose. Furthermore, irrespective of the strain involved this phenotype displayed both Ca(2+)-dependent and Ca(2+)-independent flocculation characteristics. A distinct advantage of this unique FLO11-based phenotype was highlighted in its ability to dramatically promote faster lees settling rates. Moreover, wines produced by BM45-F11H and VIN13-F11H transformants were significantly less turbid than those produced by their wild-type parental strains.

Carnitine and carnitine acetyltransferases in the yeast Saccharomyces cerevisiae: a role for carnitine in stress protection.

To date, the only reported metabolic and physiological roles for carnitine in Saccharomyces cerevisiae are related to the activity of the carnitine shuttle. In yeast, the shuttle transfers peroxisomal activated acetyl-residues to the mitochondria. However, acetyl-CoA can also be metabolised by the glyoxylate cycle to form succinate. The two pathways, therefore, provide a metabolic bypass for each other, and carnitine-dependent phenotypes have only been described in strains with non-functional peroxisomal citrate synthase, Cit2p. Here, we present evidence for a role of carnitine in stress protection that is independent of CIT2 and of the carnitine shuttle. Data show that carnitine improves growth during oxidative stress and in the presence of weak organic acids in wt and in CAT deletion strains. Our data also show that strains with single, double and triple deletions of the three CAT genes generally present identical phenotypes, but that the deletion of CAT2 decreases survival during oxidative stress in a carnitine-independent manner. Overexpression of single CAT genes does not lead to cross-complementation, suggesting a highly specific metabolic role for each enzyme. The data suggest that carnitine protects cells from oxidative and organic acid stress, while CAT2 contributes to the response to oxidative stress.