Impact of Saccharomyces cerevisiae yeast inoculation mode on wine composition

Inoculation modes are known to affect yeast behavior. Here, we characterized the impact of ADY and pre-culturing on the composition of the resulting wine, fermented by four commercial strains of Saccharomyces cerevisiae. Classical oenological parameters were not affected by the yeast inoculation mode. Using an untargeted metabolomic approach, a significant distinction in wine composition was noted regardless of the strain between the two inoculation modes, each associated with a specific metabolomic signature. 218 and 895 biomarkers were annotated, respectively, for ADYs associated with the preservation of wine polyphenols, and for pre-cultures related to the modulation of yeast nitrogen metabolism. Volatilome analysis revealed that the ester family was that most impacted by the inoculation mode whatever the strain. Ester production was enhanced in ADY condition. For the first time, the complete reprogramming of the yeast metabolism was revealed as a function of yeast preparation, which significantly impacts its volatilome and exometabolome.

Basal catalase activity and high glutathione levels influence the performance of non-Saccharomyces active dry wine yeasts

Non-Saccharomyces wine yeasts are useful tools for producing wines with complex aromas or low ethanol content. Their use in wine would benefit from their production as active dry yeast (ADY) starters to be used as co-inocula alongside S. cerevisiae. Oxidative stress during biomass propagation and dehydration is a key factor in determining ADY performance, as it affects yeast vitality and viability. Several studies have analysed the response of S. cerevisiae to oxidative stress under dehydration conditions, but not so many deal with non-conventional yeasts. In this work, we analysed eight non-Saccharomyces wine yeasts under biomass production conditions and studied oxidative stress parameters and lipid composition. The results revealed wide variability among species in their technological performance during ADY production. Also, for Metschnikowia pulcherrima and Starmerella bacillaris, better performance correlates with high catalase activity and glutathione levels. Our data suggest that non-Saccharomyces wine yeasts with an enhanced oxidative stress response are better suited to grow under ADY production conditions.

Proteomic Analysis of Saccharomyces cerevisiae Response to Oxidative Stress Mediated by Cocoa Polyphenols Extract

The present study addressed the protective effects against oxidative stress (OS) of a cocoa powder extract (CPEX) on the protein expression profile of S. cerevisiae. A proteomic analysis was performed after culture preincubation with CPEX either without stress (−OS) or under stress conditions (+OS) (5 mM of H₂O₂). LC-MS/MS identified 33 differentially expressed proteins (–OS: 14, +OS: 19) that were included By Gene Ontology analysis in biological processes: biosynthesis of amino acids, carbohydrate metabolism and reactive oxygen species metabolic process. In a gene-knockout strains study, eight proteins were identified as putative candidates for being involved in the protective mechanism of cocoa polyphenols against OS induced by H₂O₂. CPEX was able to exert its antioxidant activity in yeast mainly through the regulation of: (a) amino acids metabolism proteins by modulating the production of molecules with known antioxidant roles; (b) stress-responsive protein Yhb1, but we were unable to fully understand its down-regulation; (c) protein Prb1, which can act by clipping Histone H3 N-terminal tails that are related to cellular resistance to DNA damaging agents.

Apple bagasse as a substrate for the propagation of Patagonian wine yeast biomass

AIMS

A culture medium based on apple bagasse was designed and tested as a substrate for biomass production of conventional and unconventional native wine yeasts.

METHODS AND RESULTS

The physicochemical characterization of the apple bagasse was carried out and its potential utility as a constituent of a complete culture medium for the production of yeast biomass was analysed using the experimental statistical designs. Growth parameters of conventional and nonconventional Patagonian wine yeasts were analysed with Placket-Burman designs and response surface methodology, comparing in each assay the apple bagasse substrate with the commonly used substrate for biomass development, cane molasses. Culture media composition was optimized and models were validated.

CONCLUSIONS

This study demonstrates that, both from a nutritional and from an economic point of view, apple bagasse constitutes a more advantageous substrate than cane molasses for the propagation of native yeasts from Patagonia.

SIGNIFICANCE AND IMPACT OF THE STUDY

We used an alternate carbon-rich material, generously available in our region, originally generated as fruit industrial waste, to transform it into a source of sustainable, economically profitable and environmentally friendly energy resource.

Transcriptomic analysis of Saccharomyces cerevisiae x Saccharomyceskudriavzevii hybrids during low temperature winemaking

BACKGROUND

Although Saccharomyces cerevisiae is the most frequently isolated species in wine fermentation, and the most studied species, other species and interspecific hybrids have greatly attracted the interest of researchers in this field in the last few years, given their potential to solve new winemaking industry challenges. S. cerevisiae x S. kudriavzevii hybrids exhibit good fermentative capabilities at low temperatures, and produce wines with smaller alcohol quantities and larger glycerol quantities, which can be very useful to solve challenges in the winemaking industry such as the necessity to enhance the aroma profile.

METHODS

In this study, we performed a transcriptomic study of S. cerevisiae x S. kudriavzevii hybrids in low temperature winemaking conditions.

RESULTS

The results revealed that the hybrids have acquired both fermentative abilities and cold adaptation abilities, attributed to S. cerevisiae and S. kudriavzevii parental species, respectively, showcasing their industrially relevant characteristics. For several key genes, we also studied the contribution to gene expression of each of the alleles of S. cerevisiae and S. kudriavzevii in the S. cerevisiae x S. kudriavzevii hybrids. From the results, it is not clear how important the differential expression of the specific parental alleles is to the phenotype of the hybrids.

CONCLUSIONS

This study shows that the fermentative abilities of S. cerevisiae x S. kudriavzevii hybrids at low temperatures do not seem to result from differential expression of specific parental alleles of the key genes involved in this phenotype.

α,β-Dicarbonyl reduction is mediated by the Saccharomyces Old Yellow Enzyme

The undesirable flavor compounds diacetyl and 2,3-pentanedione are vicinal diketones (VDKs) formed by extracellular oxidative decarboxylation of intermediate metabolites of the isoleucine, leucine and valine (ILV) biosynthetic pathway. These VDKs are taken up by Saccharomyces and enzymatically converted to acetoin and 3-hydroxy-2-pentanone, respectively. Purification of a highly enriched diacetyl reductase fraction from Saccharomyces cerevisiae in conjunction with mass spectrometry identified Old Yellow Enzyme (Oye) as an enzyme capable of catalyzing VDK reduction. Kinetic analysis of recombinant Oye1p, Oye2p and Oye3p isoforms confirmed that all three isoforms reduced diacetyl and 2,3-pentanedione in an NADPH-dependent reaction. Transcriptomic analysis of S. cerevisiae (ale) and S. pastorianus (lager) yeast during industrial fermentations showed that the transcripts for OYE1, OYE2, arabinose dehydrogenase (ARA1), α-acetolactate synthase (ILV2) and α-acetohydroxyacid reductoisomerase (ILV5) were differentially regulated in a manner that correlated with changes in extracellular levels of VDKs. These studies provide insights into the mechanism for reducing VDKs and decreasing maturation times of beer which are of commercial importance.

Understanding the Mechanism of Thermotolerance Distinct From Heat Shock Response Through Proteomic Analysis of Industrial Strains of Saccharomyces cerevisiae

Saccharomyces cerevisiae has been intensively studied in responses to different environmental stresses such as heat shock through global omic analysis. However, the S. cerevisiae industrial strains with superior thermotolerance have not been explored in any proteomic studies for elucidating the tolerance mechanism. Recently a new diploid strain was obtained through evolutionary engineering of a parental industrial strain, and it exhibited even higher resistance to prolonged thermal stress. Herein, we performed iTRAQ-based quantitative proteomic analysis on both the parental and evolved industrial strains to further understand the mechanism of thermotolerant adaptation. Out of ∼ 2600 quantifiable proteins from biological quadruplicates, 193 and 204 proteins were differentially regulated in the parental and evolved strains respectively during heat-stressed growth. The proteomic response of the industrial strains cultivated under prolonged thermal stress turned out to be substantially different from that of the laboratory strain exposed to sudden heat shock. Further analysis of transcription factors underlying the proteomic perturbation also indicated the distinct regulatory mechanism of thermotolerance. Finally, a cochaperone Mdj1 and a metabolic enzyme Adh1 were selected to investigate their roles in mediating heat-stressed growth and ethanol production of yeasts. Our proteomic characterization of the industrial strain led to comprehensive understanding of the molecular basis of thermotolerance, which would facilitate future improvement in the industrially important trait of S. cerevisiae by rational engineering.

Enhanced fermentative capacity of yeasts engineered in storage carbohydrate metabolism

During yeast biomass production, cells are grown through several batch and fed-batch cultures on molasses. This industrial process produces several types of stresses along the process, including thermic, osmotic, starvation, and oxidative stress. It has been shown that Saccharomyces cerevisiae strains with enhanced stress resistance present enhanced fermentative capacity of yeast biomass produced. On the other hand, storage carbohydrates have been related to several types of stress resistance in S. cerevisiae. Here we have engineered industrial strains in storage carbohydrate metabolism by overexpressing the GSY2 gene, that encodes the glycogen synthase enzyme, and deleting NTH1 gene, that encodes the neutral trehalase enzyme. Industrial biomass production process simulations were performed with control and modified strains to measure cellular carbohydrates and fermentation capacity of the produced biomass. These modifications increased glycogen and trehalose levels respectively during bench-top trials of industrial biomass propagation. We finally show that these strains display an improved fermentative capacity than its parental strain after biomass production. Modification of storage carbohydrate content increases fermentation or metabolic capacity of yeast which can be an interesting application for the food industry.

Trx2p-dependent regulation of Saccharomyces cerevisiae oxidative stress response by the Skn7p transcription factor under respiring conditions

The whole genome analysis has demonstrated that wine yeasts undergo changes in promoter regions and variations in gene copy number, which make them different to lab strains and help them better adapt to stressful conditions during winemaking, where oxidative stress plays a critical role. Since cytoplasmic thioredoxin II, a small protein with thiol-disulphide oxidoreductase activity, has been seen to perform important functions under biomass propagation conditions of wine yeasts, we studied the involvement of Trx2p in the molecular regulation of the oxidative stress transcriptional response on these strains. In this study, we analyzed the expression levels of several oxidative stress-related genes regulated by either Yap1p or the co-operation between Yap1p and Skn7p. The results revealed a lowered expression for all the tested Skn7p dependent genes in a Trx2p-deficient strain and that Trx2p is essential for the oxidative stress response during respiratory metabolism in wine yeast. Additionally, activity of Yap1p and Skn7p dependent promoters by β-galactosidase assays clearly demonstrated that Skn7p-dependent promoter activation is affected by TRX2 gene deficiency. Finally we showed that deleting the TRX2 gene causes Skn7p hyperphosphorylation under oxidative stress conditions. We propose Trx2p to be a new positive efector in the regulation of the Skn7p transcription factor that controls phosphorylation events and, therefore, modulates the oxidative stress response in yeast.

Engineered Trx2p industrial yeast strain protects glycolysis and fermentation proteins from oxidative carbonylation during biomass propagation

BACKGROUND

In the yeast biomass production process, protein carbonylation has severe adverse effects since it diminishes biomass yield and profitability of industrial production plants. However, this significant detriment of yeast performance can be alleviated by increasing thioredoxins levels. Thioredoxins are important antioxidant defenses implicated in many functions in cells, and their primordial functions include scavenging of reactive oxygen species that produce dramatic and irreversible alterations such as protein carbonylation.

RESULTS

In this work we have found several proteins specifically protected by yeast Thioredoxin 2 (Trx2p). Bidimensional electrophoresis and carbonylated protein identification from TRX-deficient and TRX-overexpressing cells revealed that glycolysis and fermentation-related proteins are specific targets of Trx2p protection. Indeed, the TRX2 overexpressing strain presented increased activity of the central carbon metabolism enzymes. Interestingly, Trx2p specifically preserved alcohol dehydrogenase I (Adh1p) from carbonylation, decreased oligomer aggregates and increased its enzymatic activity.

CONCLUSIONS

The identified proteins suggest that the fermentative capacity detriment observed under industrial conditions in T73 wine commercial strain results from the oxidative carbonylation of specific glycolytic and fermentation enzymes. Indeed, increased thioredoxin levels enhance the performance of key fermentation enzymes such as Adh1p, which consequently increases fermentative capacity.

Modification of the TRX2 gene dose in Saccharomyces cerevisiae affects hexokinase 2 gene regulation during wine yeast biomass production

In the industrial yeast biomass production process, cells undergo an oxidative and other stresses which worsen the quality of the produced biomass. The overexpression of the thioredoxin codifying gene TRX2 in a wine Saccharomyces cerevisiae strain increases resistance to oxidative stress and industrial biomass production yield. We observed that variations in the TRX2 gene dose in wine yeast strains are relevant to determine the fermentative capacity throughout the industrial biomass production process. So, we studied the molecular changes using a transcriptomic approach under these conditions. The results provide an overview of the different metabolic pathways affected during industrial biomass production by TRX2 gene manipulation. The oxidative stress-related genes, like those related with the glutathione metabolism, presented outstanding variations. The data also allowed us to propose new thioredoxin targets in S. cerevisiae, such as hexokinase 2, with relevance for industrial fermentation performance.