Assessing the Mechanisms Responsible for Differences between Nitrogen Requirements of Saccharomyces cerevisiae Wine Yeasts in Alcoholic Fermentation

Abstract

Nitrogen is an essential nutrient for Saccharomyces cerevisiae wine yeasts during alcoholic fermentation, and its abundance determines the fermentation rate and duration. The capacity to ferment under conditions of nitrogen deficiency differs between yeasts. A characterization of the nitrogen requirements of a set of 23 strains revealed large differences in their fermentative performances under nitrogen deficiency, and these differences reflect the nitrogen requirements of the strains. We selected and compared two groups of strains, one with low nitrogen requirements (LNRs) and the other with high nitrogen requirements (HNRs). A comparison of various physiological traits indicated that the differences are not related to the ability to store nitrogen or the protein content. No differences in protein synthesis activity were detected between strains with different nitrogen requirements. Transcriptomic analysis revealed expression patterns specific to each of the two groups of strains, with an overexpression of stress genes in HNR strains and a stronger expression of biosynthetic genes in LNR strains. Our data suggest that differences in glycolytic flux may originate from variations in nitrogen sensing and signaling under conditions of starvation.

Responses of Saccharomyces cerevisiae to nitrogen starvation in wine alcoholic fermentation

“…The rate of protein synthesis is much lower in the stationary phase than during exponential growth, although it still remains moderately active during this phase. Indeed, the inhibition of protein synthesis by cycloheximide is associated with a large decrease of fermentation rate consistent with the requirement of protein synthesis to sustain fermentation flux (Brice et al 2014a;Salmon 1989). The total amount of protein exhibits only minor changes upon starvation through substantial remodeling of the proteome (Breker et al 2013;Rossignol et al 2009).…”

“…A specific method, based on the measurement of the nitrogen supply required to keep the fermentation rate constant in the stationary phase (constant rate fermentation method), has been proposed to quantify the nitrogen needs of yeast strains (Julien et al 2000;Manginot et al 1997;Manginot et al 1998). The molecular characterization of strains with different nitrogen requirements has revealed differences in gene expression between strains; those with high nitrogen requirements overexpress stress genes, whereas strains with low nitrogen needs overexpress biosynthetic genes (Brice et al 2014a). Through a QTL approach, Brice et al (2014b) identified allelic variations in several genes that affect nitrogen requirement.…”

“…Proteins account for around 40 to 50 % of yeast biomass in alcoholic fermentation (Brice et al 2014a;Varela et al 2004). The rate of protein synthesis is much lower in the stationary phase than during exponential growth, although it still remains moderately active during this phase.…”

“…Yeasts mainly use nitrogen during the growth phase in the first 24-48 h of fermentation (Brice et al 2014a;Novo et al 2005) and are rapidly starved of nitrogen, the depletion of which triggers entry into the stationary phase. Consequently, most sugar fermentation takes place in conditions of nitrogen starvation.…”

“…Fermentation kinetics in nitrogen-limited conditions (100 mg/LYAN) of a different wine yeast strains and of b one yeast strain with a high (HNR; MTF1782) and one strain with a low (LNR; MTF2029) nitrogen requirement (fromBrice et al 2014a) …”