Btn2p is involved in ethanol tolerance and biofilm formation in flor yeast

Flor yeasts are a particular kind of Saccharomyces cerevisiae strains involved in Sherry wine biological ageing. During this process, yeasts form a film on the wine surface and use ethanol as a carbon source, producing acetaldehyde as a by-product. Acetaldehyde induces BTN2 transcription in laboratory strains. Btn2p is involved in the control of the subcellular localization of different proteins. The BTN2 gene shows a complex expression pattern in wine yeast, increasing its expression by acetaldehyde, but repressing it by ethanol. A flor yeast strain transcribes more BTN2 than a first fermentation yeast during growth, but less under different stress conditions. BTN2 deletion decreases flor yeast resistance to high ethanol concentrations. Surprisingly, this effect is suppressed by the addition of high amounts of amino acids to the growth medium, indicating that the role of Btn2p protein in amino acid transport is important for ethanol resistance. Btn2p deletion increases the fermentative capacity of flor yeast and its overexpression prevents its growth on nonfermentable carbon sources. BTN2 deletion also affects the biofilm formation ability of flor yeast, and it increases its sliding motility, resulting in increased mat formation. This correlates with an increased transcription of the FLO11 gene, a gene essential for biofilm formation.