Identification and Molecular Characterization of Novel Mycoviruses in Saccharomyces and Non-Saccharomyces Yeasts of Oenological Interest

Wine yeasts can be natural hosts for dsRNA, ssRNA viruses and retrotransposon elements. In this study, high-throughput RNA sequencing combined with bioinformatic analyses unveiled the virome associated to 16 Saccharomyces cerevisiae and 8 non-Saccharomyces strains of oenological interest. Results showed the presence of six viruses and two satellite dsRNAs from four different families, two of which—Partitiviridae and Mitoviridae—were not reported before in yeasts, as well as two ORFan contigs of viral origin. According to phylogenetic analysis, four new putative mycoviruses distributed in Totivirus, Cryspovirus, and Mitovirus genera were identified. The majority of commercial S. cerevisiae strains were confirmed to be the host for helper L-A type totiviruses and satellite M dsRNAs associated with the killer phenotype, both in single and mixed infections with L-BC totiviruses, and two viral sequences belonging to a new cryspovirus putative species discovered here for the first time. Moreover, single infection by a narnavirus 20S-related sequence was also found in one S. cerevisiae strain. Considering the non-Saccharomyces yeasts, Starmerella bacillaris hosted four RNAs of viral origin—two clustering in Totivirus and Mitovirus genera, and two ORFans with putative satellite behavior. This study confirmed the infection of wine yeasts by viruses associated with useful technological characteristics and demonstrated the presence of complex mixed infections with unpredictable biological effects.

Screening and Identification of Yeasts from Fruits and Their Coculture for Cider Production

Coculturing non-Saccharomyces yeasts with Saccharomyces cerevisiae could enrich the aromatic complexity of alcoholic beverages during cider brewing. Therefore, the present study performed rapid strain screening via selective culture medium and aroma analysis and adopted a response surface methodology to optimize fermentation conditions to produce 2-phenylethyl acetate (PEA), which presents a rose and honey scent. The effects of coculturing yeasts on cider quality were evaluated through hedonic sensory analysis and the check-all-that-apply (CATA) method. Hanseniaspora vineae P5 and S. cerevisiae P1 produced ciders with high levels of PEA and 2-phenylethanol, respectively. The optimal fermentation process consisted of sequential inoculation with a 31 h delay between inoculations, followed by fermentation for 14.5 d at 18.7 °C, yielding 17.41 ± 0.51 mg/L of PEA, which was 4.6-fold higher than that obtained through the unoptimized fermentation process. Additionally, the CATA results revealed that the cider produced through coculturing was associated with descriptors such as “smooth taste”, “honey”, “pineapple”, and “fruity”, which can be attributed to the high ethyl acetate and PEA levels in the cider.

Wine Saccharomyces Yeasts for Beer Fermentation

Multiple studies in recent years have shown the potential of Saccharomyces wild yeasts to produce craft beers with new flavour profiles and other desirable properties. Yeasts isolated from food (wine, bread, kombucha…) have shown potential promise for application in brewing. The aim of this study is to evaluate the ability of 141 Saccharomyces yeast strains isolated from the Madrilenian agriculture (from grapes, must, wine, vineyard, and cellars) to produce a novel ale beer. Fermentation activity of the strains was compared against the commercial strain Saccharomyces cerevisiae Safale S-04. In addition to the other aspects such as melatonin production, thirty-three volatile compounds belonging to higher alcohols, esters, aldehydes/cetones, acids, lactones and phenolic groups, were analysed by GC for selection of the strains. Ten strains were finally chosen, among which the most relevant was the strain G 520 showing a higher production of esters, higher alcohols and acids compared with S-04. The apparent attenuation for this strain was lower than commercial strain, which translates into more residual sugars. Furthermore, G 520 was more capable of producing significantly higher amounts of melatonin studied by HPLC, as well as showing a higher antioxidant capacity. Consumer study showed that G 520 strain could be used to produce a potential beer that has a place in the current market.

Impact of Starmerella bacillaris and Zygosaccharomyces bailii on ethanol reduction and Saccharomyces cerevisiae metabolism during mixed wine fermentations

The bulk of grape juice fermentation is carried out by the yeast Saccharomyces cerevisiae, but non-Saccharomyces yeasts can modulate many sensorial aspects of the final products in ways not well understood. In this study, some of such non-conventional yeasts were screened as mixed starter cultures in a fermentation defined medium in both simultaneous and sequential inoculations. One strain of Starmerella bacillaris and another of Zygosaccharomyces bailii were chosen by their distinct phenotypic footprint and their ability to reduce ethanol levels at the end of fermentation, particularly during simultaneous vinification. S. bacillaris losses viability strongly at the end of mixed fermentation, while Z. bailii remains viable until the end of vinification. Interestingly, for most non-Saccharomyces yeasts, simultaneous inoculation helps for survival at the end of fermentation compared to sequential inoculation. S. cerevisiae viability was unchanged by the presence of the either yeast. Characterization of both strains indicates that S. bacillaris behavior is overall more different from S. cerevisiae than Z. bailii. S. bacillaris has a less strict glucose repression mechanism and molecular markers like catabolite repression kinase Snf1 is quite different in size. Besides, S. cerevisiae transcriptome changes to a bigger degree in the presence of S. bacillaris than when inoculated with Z. bailii. S. bacillaris induces the translation machinery and repress vesicular transport. Both non-Saccharomyces yeast induce S. cerevisiae glycolytic genes, and that may be related to ethanol lowering, but there are specific aspects of carbon-related mechanisms between strains: Z. bailii presence increases the stress-related polysaccharides trehalose and glycogen while S. bacillaris induces gluconeogenesis genes.