Sulfate transport mutants affect hydrogen sulfide and sulfite production during alcoholic fermentation

Sulphate Uptake Plays a Major Role in the Production of Sulphur Dioxide by Yeast Cells during Oenological Fermentations

Sulphur dioxide (SO2) is mostly used as an antioxidant additive in winemaking, but excessive levels may be harmful to both wine quality and consumers health. During fermentation, yeast Saccharomyces cerevisiae contributes significantly to final SO2 levels, and low-producing strains become especially interesting for the wine industry. Recent evidence implicating the impairment of sulphate transport in the SO2 decrease prompted us to further investigate the sulphate/sulphite metabolic connection in multiple winery yeast strains. Here, we inactivated by CRISPR/Cas9 the high-affinity sulphate permeases (Sul1p and Sul2p) in four strains normally used in winemaking, selected by their different abilities to produce SO2. Mutant strains were then used to perform fermentation assays in different types of natural must, and the final levels of SO2 and other secondary metabolites, crucial for wine organoleptic properties, were further determined for all fermentation products. Overall, data demonstrated the double ΔSUL1/ΔSUL2 inactivation in winery strains significantly decreases the levels of SO2 produced by mutant cells, without however altering both yeast fermentative properties and the ability to release relevant metabolites. Since similar effects were observed in diverse must types for strains with different features, the data strongly support that sulphate assimilation is the determining factor in SO2 production during oenological fermentations.

Advances in pathogenesis and therapeutic strategies for osteoporosis

Osteoporosis, is the most common bone disorder worldwide characterized by low bone mineral density, leaving affected bones vulnerable to fracture. Bone homeostasis depends on the precise balance between bone resorption by osteoclasts and bone matrix formation by mesenchymal lineage osteoblasts, and involves a series of complex and highly regulated steps. Bone homeostasis will be disrupted when the speed of bone resorption is faster than bone formation. Based on various regulatory mechanisms of bone homeostasis, a series of drugs targeting osteoporosis have emerged in clinical practice, including bisphosphonates, selective estrogen receptor modulators, calcitonin, molecular-targeted drugs and so on. However, many drugs have major adverse effects or are unsuitable for long-term use. Therefore, it is very urgent to find more effective therapeutic drugs based on the new pathogenesis of osteoporosis. In this review, we summarize novel mechanisms involved in the pathological process of osteoporosis, including the roles of gut microbiome, autophagy, iron balance and cellular senescence. Based on the above pathological mechanism, we found promising drugs for osteoporosis treatment, such as: probiotics, alpha-ketoglutarate, senolytics and hydrogen sulfide. This new finding may provide an important basis for elucidating the complex pathological mechanisms of osteoporosis and provide promising drugs for clinical osteoporosis treatment.

Disruption of ECM33 in diploid wine yeast EC1118: cell morphology and aggregation and their influence on fermentation performance

When investigating yeast gene function in relation to fermentation, many screens rely on haploid yeast derivatives. This, however, is not representative of industrial strains, which are typically diploid. One such example is the disruption of ECM33, which was associated with improved fermentation in the haploid wine yeast C911D, but remains uncharacterised in a diploid industrial strain background. We report on the homozygous disruption of ECM33 in Lalvin EC1118 using CRISPR/Cas9. EC1118 ecm33 resulted in a reduction of fermentation duration in a defined medium with limiting and sufficient nitrogen (-20% and -13%, respectively) when shaken. Increased cell size and aggregation, a phenotype previously unidentified in ecm33∆ as haploid yeast tend to aggregate, was also observed. This phenotype led to premature settling thereby the yeast behaving similarly to EC1118 in wine-like semi-static fermentations in a chemically defined medium. Further assessment in semi-static Riesling and Chardonnay fermentations inoculated based on cell number or biomass resulted in no significant difference or significantly slower fermentation duration in comparison the EC1118, nullifying the benefits of this mutation unless agitation is applied. This study draws attention to phenotypes being condition-dependent, highlighting the need to characterise and verify fermentation efficiency mutations in industrial yeast.

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.