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Background: Connecting the composition and function of industrial microbiomes is a major aspiration in microbial biotechnology. Here, we address this question in wine fermentation, a model system where the diversity and functioning of fermenting yeast species are determinant of the flavor and quality of the resulting wines. Results: First, we surveyed yeast communities associated with grape musts collected across wine appellations, revealing the importance of environmental (i.e., biogeography) and anthropic factors (i.e., farming system) in shaping community composition and structure. Then, we assayed the fermenting yeast communities in synthetic grape must under common winemaking conditions. The dominating yeast species defines the fermentation performance and metabolite profile of the resulting wines, and it is determined by the initial fungal community composition rather than the imposed fermentation conditions. Yeast dominance also had a more pronounced impact on wine meta-transcriptome than fermentation conditions. We unveiled yeast-specific transcriptomic profiles, leveraging different molecular functioning strategies in wine fermentation environments. We further studied the orthologs responsible for metabolite production, revealing modules associated with the dominance of specific yeast species. This emphasizes the unique contributions of yeast species to wine flavor, here summarized in an array of orthologs that defines the individual contribution of yeast species to wine ecosystem functioning. Conclusions: Our study bridges the gap between yeast community composition and wine metabolite production, providing insights to harness diverse yeast functionalities with the final aim to producing tailored high-quality wines. 74dL8hDE5Rym1TqBfqxSSD Video Abstract [ABSTRACT FROM AUTHOR]

Malolactic fermentation (MLF) in wine is driven by the lactic acid bacterium Oenococcus oeni in most cases. Although this bacterium is resistant to wine stress conditions, it often faces difficulties completing MLF. Previous studies indicate that yeast mannoproteins may improve O. oeni growth and survival in wine. However, very little is known about this topic. This study evaluated the effect of the addition of mannoprotein extracts to culture media on O. oeni growth and its survival to stress conditions and MLF performance. Three commercial mannoprotein extracts were characterized in terms of polysaccharide and protein richness and were used for O. oeni culture media supplementation. The addition of mannoprotein extracts improved the survival of the two evaluated O. oeni strains, PSU-1 and VP41, after acid shock (pH 3.2) in comparison to that of the control. The transcriptional response of four genes involved in mannose metabolism was different depending on the strain, indicating the complexity of sugar metabolism in O. oeni. PSU-1 cells grown with two of the mannoprotein extracts performed faster MLF compared with the control condition, indicating that mannoprotein addition may improve the performance of O. oeni starter cultures, although this effect depends on the strain. [ABSTRACT FROM AUTHOR]

Sulfur dioxide is the most used additive today for preventing browning in grape musts and wines. However, since wine consumers are increasingly interested in healthier wines, the wine industry is keen to reduce its use. Some promising alternatives to sulfur dioxide have been proposed in recent years, including glutathione, both pure and in the form of inactivated yeasts, and Metschnikowia pulcherrima used as a bioprotective agent. Some information exists about the protective effect against oxidation of glutathione but there is very few about the use of bioprotection for that purpose. Supplementation with glutathione, regardless of the commercial form, reduced oxygen consumption and browning intensity when laccase was not present in the grape juice. Metschnikowia pulcherrima also reduced browning intensity in the absence of laccase but increased the total oxygen consumption. However, in the presence of laccase, glutathione and Metschnikowia pulcherrima were not effective enough to adequately prevent the grape juice from browning. Glutathione, both pure and in the form of inactivated yeasts, and Metschnikowia pulcherrima are interesting tools for protecting grape must against browning, and thus reducing the use of sulfur dioxide. [ABSTRACT FROM AUTHOR]

Saccharomyces cerevisiae is a highly fermentative species able to complete the wine fermentation. However, the interaction with other non- Saccharomyces yeasts can determine the fermentation performance of S. cerevisiae. We have characterised three rare non- Saccharomyces yeasts (Cyberlindnera fabianii , Kazachstania unispora and Naganishia globosa), studying their impact on S. cerevisiae fitness and wine fermentation performance. Using a wide meta-taxonomic dataset of wine samples, analysed through ITS amplicon sequencing, we show that about a 65.07% of wine samples contains Naganishia spp., a 27.21% contains Kazachstania spp., and only a 4.41% contains Cyberlindnera spp; in all cases with average relative abundances lower than 1% of total fungal populations. Although the studied N. globosa strain showed a limited growth capacity in wine, both K. unispora and C. fabianii showed a similar growth phenotype to that of S. cerevisiae in different fermentation conditions, highlighting the outstanding growth rate values of K. unispora. In mixed fermentations with S. cerevisiae , the three yeast species affected co-culture growth parameters and wine chemical profile (volatile compounds, polysaccharides and proteins). K. unispora DN201 strain presents an outstanding capacity to compete with S. cerevisiae strains during the first stage of wine fermentation, causing stuck fermentations in both synthetic and natural grape musts. • The prevalence of Cyberlindnera spp. in wine populations is about 4% of samples. • The prevalence of Kazachstania spp. in wine populations is about 27% of samples. • The prevalence of Naganishia spp. in wine populations is about 65% of samples. • Kazachstania unispora DN201 caused stuck fermentations. • K.unispora DN201 has high nitrogen consumption rate and production of acetic acid. [ABSTRACT FROM AUTHOR]