Transcriptional Response ofSaccharomyces cerevisiaeto Different Nitrogen Concentrations during Alcoholic Fermentation

Abstract

Gene expression profiles of a wine strain of Saccharomyces cerevisiae PYCC4072 were monitored during alcoholic fermentations with three different nitrogen supplies: (i) control fermentation (with enough nitrogen to complete sugar fermentation), (ii) nitrogen-limiting fermentation, and (iii) the addition of nitrogen to the nitrogen-limiting fermentation (refed fermentation). Approximately 70% of the yeast transcriptome was altered in at least one of the fermentation stages studied, revealing the continuous adjustment of yeast cells to stressful conditions. Nitrogen concentration had a decisive effect on gene expression during fermentation. The largest changes in transcription profiles were observed when the early time points of the N-limiting and control fermentations were compared. Despite the high levels of glucose present in the media, the early responses of yeast cells to low nitrogen were characterized by the induction of genes involved in oxidative glucose metabolism, including a significant number of mitochondrial associated genes resembling the yeast cell response to glucose starvation. As the N-limiting fermentation progressed, a general downregulation of genes associated with catabolism was observed. Surprisingly, genes encoding ribosomal proteins and involved in ribosome biogenesis showed a slight increase during N starvation; besides, genes that comprise the RiBi regulon behaved distinctively under the different experimental conditions. Here, for the first time, the global response of nitrogen-depleted cells to nitrogen addition under enological conditions is described. An important gene expression reprogramming occurred after nitrogen addition; this reprogramming affected genes involved in glycolysis, thiamine metabolism, and energy pathways, which enabled the yeast strain to overcome the previous nitrogen starvation stress and restart alcoholic fermentation.

Reconciling Competing Models: A Case Study of Wine Fermentation Kinetics

“…In our study we considered experimental data of three papers: [22], [15] and [16]. The experimental measures of the Pizarro team correspond to a wide range of data.…”

“…In particular the Pizarro sample for HMM (high temperature, moderate initial sugar level and moderate initial nitrogen level) and HMH configurations give us standard deviations for variable profiles. Mendes-Ferreira ( [16]) samples for MHM (moderate temperature, high initial sugar level and moderate initial nitrogen level) and MHH supply means and standard deviations of measures too.…”

“…In Table 4 we summarize our criteria, and according to initial conditions and variable to consider (between Biomass, Ethanol and Sugar) we say which approach to use. We used the criteria to build a combined model where we separate the different effects in polynomial way to obtain a combined model (equations [16][17][18] Table 5: Statistical analysis of models. For each configuration of factors and fermentation variable, we show the average p-value for the local criterion (C.1), and correlation for global criterion (C.2).…”

“…By direct communication with [15], we obtained data of biomass profiles in two particular conditions: moderate temperature (24 • C), high level of sugar (280 g/l) and moderate/high levels of nitrogen (approximately 220 mg/l and 551 mg/l respectively). The data set available in Mendes-Ferreira studie ( [16]) used the strain Saccharomyces cerevisiae PYCC4072 that was supplied by the Portuguese Yeast Culture Collection. The paper describes experimental biomass, ethanol and sugar (and other indexes) results for two experimental conditions, fermentation maintained at 20 • C with moderate initial sugar concentration (200 g/l) and initial nitrogen concentration high (267 mg/l) or low (66 mg/l).…”

Wine Science in the Omics Era: The Impact of Systems Biology on the Future of Wine Research

“…Several transcriptomic studies have also been published for research conducted with wine yeast strains (Erasmus et al, 2003;Rossignol et al, 2003;Varela et al, 2005;Mendes-Ferreira et al, 2007;Marks et al, 2008;Pizarro et al, 2008;Rossouw & Bauer, 2008). These studies have illuminated the intrinsic genetic and regulatory mechanisms involved in fermentation, and have greatly increased our understanding of this important process.…”