Effect of nutrient depletion on parietal adsorption activity of Saccharomyces cerevisiae selected for winemaking (intervento orale)

The aim of this work was to investigate the effect of carbon and nitrogen availability on colour adsorption activity of selected wine yeasts, testing them in poor and rich media in the presence of coloured phenolic compounds from grape skins. Eleven autochthonous Calabrian yeast strains of the species Saccharomyces cerevisiae - previously selected as wine starter based on their different aptitude to adsorb grape pigments on their cell-wall - and 2 control strains of S. cerevisiae BY4742 and Σ1278b were grown on (a) grape skin agar (1), containing black grape skin powder 4% and dextrose 5%, 2% or 0.1%, (b) synthetic low ammonium dextrose agar (2) supplemented with black grape skin powder 4% and containing dextrose 2% or 0.1%, and (c) yeast peptone dextrose agar as control medium. After incubation at 28°C for 10 days, strains were processed for Red-Green-Blue analysis by Photoshop CS, that gives low or high values for yeast able (dark biomass) or unable (light biomass) to adsorb coloured compounds, respectively. The effect of nutrient availability is not univocal for the 13 yeast strains that exhibit significant differences for the colour parameters. Interestingly, depletion in (a) nitrogen or (b) carbon and nitrogen determines a decrease in the yeast adsorption activity, possibly due to yeast overcoming nutrient stress by phenolic compounds that seem to have a role as nutrient supplements. There is ample evidence for the effects of nutrient depletion on transcriptional activation or repression of specific genes in Saccharomyces cerevisiae, as those connected to pseudohyphal growth and flocculation. The relevant literature and the present results have been discussed considering, above all, the oenological consequences for wine starter selection.(1) Caridi A., Sidari R., Solieri L., Cufari A., Giudici P. (2007).Wine colour adsorption phenotype: an inheritable quantitative trait loci of yeasts. Journal of Applied Microbiology 103, 735-742.(2) Zaragoza O., Gancedo J.M. (2000). Pseudohyphal growth is induced in Saccharomyces cerevisiae by a combination of stress and cAMP signalling. Antonie van Leeuwenhoek 78, 187-194.