Saccharomyces cerevisiae nutrient signaling pathways show an unexpected early activation pattern during winemaking

Up-regulation of Retrograde Response in yeast increases glycerol and reduces ethanol during wine fermentation

Nutrient signaling pathways play a pivotal role in regulating the balance among metabolism, growth and stress response depending on the available food supply. They are key factors for the biotechnological success of the yeast Saccharomyces cerevisiae during food-producing fermentations. One such pathway is Retrograde Response, which controls the alpha-ketoglutarate supply required for the synthesis of amino acids like glutamate and lysine. Repressor MKS1 is linked with the TORC1 complex and negatively regulates this pathway. Deleting MKS1 from a variety of industrial strains causes glycerol to increase during winemaking, brewing and baking. This increase is accompanied by a reduction in ethanol production during grape juice fermentation in four commercial wine strains. Interestingly, this does not lead volatile acidity to increase because acetic acid levels actually lower. Aeration during winemaking usually increases acetic acid levels, but this effect reduces in the MKS1 mutant. Despite the improvement in the metabolites of oenological interest, it comes at a cost given that the mutant shows slower fermentation kinetics when grown in grape juice, malt and laboratory media and using glucose, sucrose and maltose as carbon sources. The deletion of RTG2, an activator of Retrograde Response that acts as an antagonist of MKS1, also results in a defect in wine fermentation speed. These findings suggest that the deregulation of this pathway causes a fitness defect. Therefore, manipulating repressor MKS1 is a promising approach to modulate yeast metabolism and to produce low-ethanol drinks.

Proxies introduce bias in decoding TORC1 activity

The eukaryotic TORC1 kinase integrates and links nutritional, energy, and hormonal signals to cell growth and homeostasis, and its deregulation is associated with human diseases including neurodegeneration, cancer, and metabolic syndrome. Quantification of TORC1 activities in various genetic settings and defined physiological conditions generally relies on the assessment of the phosphorylation level of residues in TORC1 targets. Here we show that two commonly used TORC1 effectors in yeast, namely Sch9 and Rps6, exhibit distinct phosphorylation patterns in response to rapamycin treatment or changes in nitrogen availability, indicating that the choice of TORC1 proxies introduces a bias in decoding TORC1 activity.

Increased Accumulation of Ginsenosides in Panax ginseng Sprouts Cultivated with Kelp Fermentates

Currently, new agri-tech has been developed and adapted for the cultivation of crops using smart farming technologies, e.g., plant factories and hydroponics. Kelp (Laminaria japonica), which has a high industrial value, was considered as an alternative to chemicals for its eco-friendly and sustainably wide use in crop cultivation. In this study, a fermented kelp (FK) was developed for use in hydroponics. The FK contained various free and protein-bound amino acid compositions produced by fermenting the kelp with Saccharomyces cerevisiae. Supplementing FK as an aeroponic medium when cultivating ginseng sprouts (GSs) elevated the total phenolic and flavonoid contents. Additionally, seven ginsenosides (Rg1, Re, Rb1, Rc, Rg2, Rb2, and Rd) in GSs cultivated with FK in a smart-farm system were identified and quantified by a high-performance liquid chromatography-evaporative light scattering detector/mass spectrometry analysis. Administering FK significantly increased the ginsenosides in the GSs compared to the control group, which was cultivated with tap water. These results indicate the FK administration contributed to the increased accumulation of ginsenosides in the GSs. Overall, this study suggests that FK, which contains abundant nutrients for plant growth, can be used as a novel nutrient solution to enhance the ginsenoside content in GSs during hydroponic cultivation.

Microbe-loaded bioink designed to support therapeutic yeast growth

Live biotherapeutic products (LBPs) are an emerging class of therapeutics comprised of engineered living organisms such as bacteria or yeast. Bioprinting with living materials has now become possible using modern three-dimensional (3D) printing strategies. While there has been significant progress in bioprinting cells, bioprinting LBPs, specifically yeast, remains in its infancy and has not been optimized. Yeasts are a promising platform to develop into protein biofactories because they (1) grow rapidly, (2) are easy to engineer and manufacture, and (3) are inexpensive to produce. Here we developed an optimized method for loading yeast into hydrogel patches using digital light processing (DLP) 3D printing. We assessed the effects of patch geometry, bioink composition, and yeast concentration on yeast viability, patch stability, and protein release, and in doing so developed a patch formulation capable of supporting yeast growth and sustained protein release for at least ten days.

Cat8 Response to Nutritional Changes and Interaction With Ehrlich Pathway Related Factors

Cat8 is an important transcription factor regulating the utilization of non-fermentative carbon sources in Saccharomyces cerevisiae. However, our previous studies found that Cat8 may play a critical role in nitrogen metabolism, but the regulatory mechanism has not been elucidated. In this study, the nuclear localization and analysis of regulatory activity showed that the Cat8 function relies on Snf1 kinase. In the fermentation with glucose or glycerol as carbon sources under phenylalanine (Phe) induction, by comparing the changes of cellular gene expression and Cat8 target gene binding profiles after Cat8 overexpression, enhanced transcription was shown among key genes involved in the Ehrlich pathway (e.g., ARO9, ARO10, and ADH2) and its upstream and downstream related factors (e.g., GAP1, AGP1, GAT1, PDR12, and ESPB6), indicating that Cat8 participated in the regulation of nitrogen metabolism. Moreover, highly active Cat8 interacts with transcriptional activator Aro80 and GATA activator Gat1 coordinately to regulate the transcription of ARO10. Altogether, our results showed that Cat8 may act as a global transcription factor in response to nutritional changes, regulating both carbon and nitrogen utilization. This provides a new insight for us to explore the regulation of cell nutrient metabolism networks in yeast.

Mechanisms of Metabolic Adaptation in Wine Yeasts: Role of Gln3 Transcription Factor

Wine strains of Saccharomyces cerevisiae have to adapt their metabolism to the changing conditions during their biotechnological use, from the aerobic growth in sucrose-rich molasses for biomass propagation to the anaerobic fermentation of monosaccharides of grape juice during winemaking. Yeast have molecular mechanisms that favor the use of preferred carbon and nitrogen sources to achieve such adaptation. By using specific inhibitors, it was determined that commercial strains offer a wide variety of glucose repression profiles. Transcription factor Gln3 has been involved in glucose and nitrogen repression. Deletion of GLN3 in two commercial wine strains produced different mutant phenotypes and only one of them displayed higher glucose repression and was unable to grow using a respiratory carbon source. Therefore, the role of this transcription factor contributes to the variety of phenotypic behaviors seen in wine strains. This variability is also reflected in the impact of GLN3 deletion in fermentation, although the mutants are always more tolerant to inhibition of the nutrient signaling complex TORC1 by rapamycin, both in laboratory medium and in grape juice fermentation. Therefore, most aspects of nitrogen catabolite repression controlled by TORC1 are conserved in winemaking conditions.

Truth in wine yeast

Evolutionary history and early association with anthropogenic environments have made Saccharomyces cerevisiae the quintessential wine yeast. This species typically dominates any spontaneous wine fermentation and, until recently, virtually all commercially available wine starters belonged to this species. The Crabtree effect, and the ability to grow under fully anaerobic conditions, contribute decisively to their dominance in this environment. But not all strains of Saccharomyces cerevisiae are equally suitable as starter cultures. In this article, we review the physiological and genetic characteristics of S. cerevisiae wine strains, as well as the biotic and abiotic factors that have shaped them through evolution. Limited genetic diversity of this group of yeasts could be a constraint to solving the new challenges of oenology. However, research in this field has for many years been providing tools to increase this diversity, from genetic engineering and classical genetic tools to the inclusion of other yeast species in the catalogues of wine yeasts. On occasion, these less conventional species may contribute to the generation of interspecific hybrids with S. cerevisiae. Thus, our knowledge about wine strains of S. cerevisiae and other wine yeasts is constantly expanding. Over the last decades, wine yeast research has been a pillar for the modernisation of oenology, and we can be confident that yeast biotechnology will keep contributing to solving any challenges, such as climate change, that we may face in the future.

Next Generation Winemakers: Genetic Engineering in Saccharomyces cerevisiae for Trendy Challenges

The most famous yeast of all, Saccharomyces cerevisiae, has been used by humankind for at least 8000 years, to produce bread, beer and wine, even without knowing about its existence. Only in the last century we have been fully aware of the amazing power of this yeast not only for ancient uses but also for biotechnology purposes. In the last decades, wine culture has become and more demanding all over the world. By applying as powerful a biotechnological tool as genetic engineering in S. cerevisiae, new horizons appear to develop fresh, improved, or modified wine characteristics, properties, flavors, fragrances or production processes, to fulfill an increasingly sophisticated market that moves around 31.4 billion € per year.