Genome Features of a New Double-Stranded RNA Helper Virus (LBCbarr) from Wine Torulaspora delbrueckii Killer Strains

The killer phenotype of Torulaspora delbrueckii (Td) and Saccharomyces cerevisiae (Sc) is encoded in the genome of medium-size dsRNA viruses (V-M). Killer strains also contain a helper large size (4.6 kb) dsRNA virus (V-LA) which is required for maintenance and replication of V-M. Another large-size (4.6 kb) dsRNA virus (V-LBC), without known helper activity to date, may join V-LA and V-M in the same yeast. T. delbrueckii Kbarr1 killer strain contains the killer virus Mbarr1 in addition to two L viruses, TdV-LAbarr1 and TdV-LBCbarr1. In contrast, the T. delbrueckii Kbarr2 killer strain contains two M killer viruses (Mbarr1 and M1) and a LBC virus (TdV-LBCbarr2), which has helper capability to maintain both M viruses. The genomes of TdV-LBCbarr1 and TdV-LBCbarr2 were characterized by high-throughput sequencing (HTS). Both RNA genomes share sequence identity and similar organization with their ScV-LBC counterparts. They contain all conserved motifs required for translation, packaging, and replication of viral RNA. Their Gag-Pol amino-acid sequences also contain the features required for cap-snatching and RNA polymerase activity. However, some of these motifs and features are similar to those of LA viruses, which may explain that at least TdV-LBCbarr2 has a helper ability to maintain M killer viruses. Newly sequenced ScV-LBC genomes contained the same motifs and features previously found in LBC viruses, with the same genome location and secondary structure. Sequence comparison showed that LBC viruses belong to two clusters related to each species of yeast. No evidence for associated co-evolution of specific LBC with specific M virus was found. The presence of the same M1 virus in S. cerevisiae and T. delbrueckii raises the possibility of cross-species transmission of M viruses.

Analyzing the minor volatilome of Torulaspora delbrueckii in an alcoholic fermentation

Torulaspora delbrueckii is an emerging yeast species in the beverage and food industry that is suitable for alcoholic fermentation and to improve the organoleptic quality of wine, beer, mead, and other beverages. Modern consumer preference toward new flavors and products drives the application of T. delbrueckii to ferment less traditional fruits and vegetables. Thus, it has become increasingly relevant to define those metabolites produced in minute quantities by T. delbrueckii, because they may have an impact when producing these new alcoholic beverages. In this study, we have identified metabolites of T. delbrueckii and have compared them with those of Saccharomyces cerevisiae in a controlled setting with a synthetic, high glucose medium using gas chromatography coupled to flame ionization detector (GC–FID) and stir bar sorptive extraction (SBSE) with GC coupled to mass spectrometry (MS). Results showed that T. delbrueckii produced metabolites with higher changes in odor activity complexes than S. cerevisiae: ethyl propanoate, 1,1-diethoxyethane, ethyl isobutyrate, ethyl butyrate, isoamyl acetate, ethyl heptanoate, nonanal, and decanal. We also report seven metabolites detected for the first time in T. delbrueckii. This datum serves to expand the knowledge of T. delbrueckii performance and shows that application of this yeast species is more suitable to a wide array of beverage producers.

The Influence of Fermenting Yeast on the Sensory Properties of Graševina Wine

Recent research has showed a breakthrough in investigating the effect of non-Saccharomyces yeast on wine quality and sensory properties. The aim of this study was to compare the influence of conventional yeast, Saccharomyces cerevisiae, vs. that of the non-Saccharomyces Torulaspora delbrueckii on the sensory profile of the white wine Graševina, and to establish if there are any differences in physical–chemical properties in regards to the applied yeast. Sample One was inoculated with both yeasts, while Sample Two was inoculated only with S. cerevisiae. The results indicated that a combination of T. delbrueckii and S. cerevisiae resulted in somewhat higher ethanol content in the finished wine. Sensory evaluation showed no significant discrepancies for any of the wines. Aspect and flavor were graded similarly, but the quality and intensity of the bouquet of Sample One was graded somewhat higher (14 and 6.6) than Sample Two (13.6 and 6.4). These findings open a very wide gate for future research in white wines.

A glimpse at an early stage of microbe domestication revealed in the variable genome of Torulaspora delbrueckii, an emergent industrial yeast

The yeast Torulaspora delbrueckii is gaining importance for biotechnology due to its ability to increase wine sensorial complexity and for enhancing pre-frozen bread dough leavening. However, little is known about its population structure, variation in gene content, or possible domestication routes. Here, we address these issues and update the delimitation of T. delbrueckii along five major clades. Among the three European clades, a basal lineage is associated with the wild arboreal niche, while the two other lineages are linked with anthropic environments, one to wine fermentations and the other to diverse sources including dairy products and bread dough (Mix- Anthropic clade). Using 62 genomes we identified 5629 genes in the pangenome of T. delbrueckii and 270 genes in the cloud genome. A pangenome tree analysis showed that wine strains have a genome composition more similar to European wild arboreal strains than to those of the Mix Anthropic clade, in contradiction with the phylogenetic analysis. An association of gene content and ecology gave further support to the hypothesis that the Mix - Anthropic clade has the most specialized genome content and indicated that some of the exclusive genes were implicated in galactose and maltose utilization. More detailed analyses traced the acquisition of a cluster of GAL genes in strains associated with dairy products and the expansion and functional diversification of MAL genes in strains isolated from bread dough. Contrary to S. cerevisiae, domestication in T. delbrueckii is not primed by alcoholic fermentation and appears to be a recent event.

Biotechnological Importance of Torulaspora delbrueckii: From the Obscurity to the Spotlight

Torulaspora delbrueckii has attracted interest in recent years, especially due to its biotechnological potential, arising from its flavor- and aroma-enhancing properties when used in wine, beer or bread dough fermentation, as well as from its remarkable resistance to osmotic and freezing stresses. In the present review, genomic, biochemical, and phenotypic features of T. delbrueckii are described, comparing them with other species, particularly with the biotechnologically well-established yeast, Saccharomyces cerevisiae. We conclude about the aspects that make this yeast a promising biotechnological model to be exploited in a wide range of industries, particularly in wine and bakery. A phylogenetic analysis was also performed, using the core proteome of T. delbrueckii, to compare the number of homologous proteins relative to the most closely related species, understanding the phylogenetic placement of this species with robust support. Lastly, the genetic tools available for T. delbrueckii improvement are discussed, focusing on adaptive laboratorial evolution and its potential.

Commercially Available Non-Saccharomyces Yeasts for Winemaking: Current Market, Advantages over Saccharomyces, Biocompatibility, and Safety

About 42 commercial products based on non-Saccharomyces yeasts are estimated as available on the market, being mostly pure cultures (79%), with a predominance of Torulaspora delbrueckii, Lachancea thermotolerans, and Metschnikowia pulcherrima. The others are multi-starter consortia that include non-Saccharomyces/Saccharomyces mixtures or only non-Saccharomyces species. Several commercial yeasts have shown adequate biocompatibility with S. cerevisiae in mixed fermentations, allowing an increased contribution of metabolites of oenological interest, such as glycerol, esters, higher alcohols, acids, thiols, and terpenes, among others, in addition to a lower production of acetic acid, volatile phenols, biogenic amines, or urea. Multi-starter inoculations are also reviewed here, which show adequate biocompatibility and synergy between species. In certain cases, the aromatic profile of wines based on grape varieties considered neutral is improved. In addition, several yeasts show the capacity as biocontrollers against contaminating microorganisms. The studies conducted to date demonstrate the potential of these yeasts to improve the properties of wine as an alternative and complement to the traditional S. cerevisiae.

Selection Process of a Mixed Inoculum of Non-Saccharomyces Yeasts Isolated in the D.O.Ca. Rioja

The use of non-Saccharomyces yeasts in sequential fermentations with S. cerevisiae has been proposed to improve the organoleptic characteristics involved in the quality of wine. The present study set out to select a non-Saccharomyces inoculum from the D.O.Ca. Rioja for use in winemaking. Strains included in the study belonged to Torulaspora delbrueckii, Lachancea thermotolerans, Metschnikowia pulcherrima, Zygosaccharomyces bailii, Williopsis pratensis, Debaryomyces hansenii, Pichia kluyveri, Sporidiobolus salmonicolor, Candida spp., Cryptococcus spp. and two mixed inocula of Lachancea thermotolerans-Torulaspora delbrueckii in a 30/70 ratio. In the first stage of the process, SO2 resistance and presence of enzymatic activities related to wine aroma and wine color and fining (esterase, esterase-lipase, lipase, leucine arylamidase, valine arylamidase, cystine arylamidase, β-glucosidase, pectinase, cellulose, xylanase and glucanase) were studied. In the later stages, selection criteria such as fermentative behavior, aroma compound production or influence on phenolic compounds were studied in laboratory scale vinifications. Taking into account the results obtained in the different stages of the process, a mixed inoculum of Lachancea thermotolerans-Torulaspora delbrueckii in a 30/70 ratio was finally selected. This inoculum stood out for its high implantation capacity, the production of compounds of interest such as glycerol and lactic acid and the consequent modulation of wine acidity. Given these characteristics, the selected inoculum is suitable for the production of quality wines.