BioProject

The yeast Dekkera bruxellensis is as ethanol tolerant as Saccharomyces cerevisiae and may be found in bottled wine. More...

The yeast Dekkera bruxellensis is as ethanol tolerant as Saccharomyces cerevisiae and may be found in bottled wine. It causes the spoilage of wine, beer, cider and soft drinks. In wines, the metabolic products responsible for spoilage by Dekkera bruxellensis are mainly volatile phenols. These chemical compounds are responsible for the taints described as ‘‘medicinal’’ in white wines (due to vinyl phenols) and as ‘‘leather’’, ‘‘horse sweat’’ and ‘‘stable’’ in red wines (due to ethyl phenols mainly 4-ethylphenol). Apart from the negative aroma nuances imparted by these yeasts, positive aromas such as ‘smoky’, ‘spicy’ and ‘toffee’ are also cited. Our goal was to identify the impact that the wine spoilage yeast Dekkera bruxellensis has on fermenting S. cerevisiae cells, especially on its gene expression level. To this end we co-inoculated both yeast species at the start of fermentation in a synthetic wine must, using S. cerevisiae-only fermentations without Dekkera bruxellensis as a control. All fermentations were employed in special membrane reactors (1.2 um pore size cut-off) physically separating Dekkera bruxellensis from wine yeast S. cerevisiae. Biomass separation with this membrane was done to abolish the possibility of hybridizing also D. bruxellensis probes on Agilent V2 (8x15K format) G4813 DNA microarrays designed just for S. cerevisiae ORF targets. The 1.2 um pore membrane separating both yeasts allowed the exchange of ethanol, metabolites and sugars during the fermentation. Overall design: Fermentations were carried out in synthetic wine must in duplicate for both the control S. cerevisiae (strain Lalvin EC1118) and mixed fermentation. Sampling of yeast S. cerevisiae for RNA extractions were performed at 22 h of fermentation, during the exponential growth phase of S. cerevisiae, at 92 h and 144 h of fermentation, during its early and late stationary growth phase and at 187 h of fermentation, during its phase of growth decline. Less...