Osmotolerant Zygosaccharomyces Rouxii Research Articles

Vinification without Saccharomyces: Interacting Osmotolerant and "Spoilage" Yeast Communities in Fermenting and Ageing Botrytised High-Sugar Wines (Tokaj Essence).

The conversion of grape juice to wine starts with complex yeast communities consisting of strains that have colonised the harvested grape and/or reside in the winery environment. As the conditions in the fermenting juice gradually become inhibitory for most species, they are rapidly overgrown by the more adaptable Saccharomyces strains, which then complete the fermentation. However, there are environmental factors that even Saccharomyces cannot cope with. We show that when the sugar content is extremely high, osmotolerant yeasts, usually considered as “spoilage yeasts“, ferment the must. The examination of the yeast biota of 22 botrytised Tokaj Essence wines of sugar concentrations ranging from 365 to 752 g∙L−1 identified the osmotolerant Zygosaccharomyces rouxii, Candida (Starmerella) lactis-condensi and Candida zemplinina (Starmerella bacillaris) as the dominating species. Ten additional species, mostly known as osmotolerant spoilage yeasts or biofilm-producing yeasts, were detected as minor components of the populations. The high phenotypical and molecular (karyotype, mtDNA restriction fragment length polymorphism (RFLP) and microsatellite-primed PCR (MSP-PCR)) diversity of the conspecific strains indicated that diverse clones of the species coexisted in the wines. Genetic segregation of certain clones and interactions (antagonism and crossfeeding) of the species also appeared to shape the fermenting yeast biota.

Genomic Insights Into Sugar Adaptation in an Extremophile Yeast Zygosaccharomyces rouxii.

The osmotolerant Zygosaccharomyces rouxii is known for its trait to survive in extreme high sugar environments. This ability determines its role in the fermentation process and leads to yeast spoilage in the food industry. However, our knowledge of the gene expression in response to high sugar stress remains limited. Here, we conducted RNA-sequencing (RNA-seq) under different sugar concentrations of the spoilage yeast, Z. rouxii, which exhibit extremely high tolerance to sugar stress. The obtained differentially expressed genes (DEGs) are significantly different to that of the Saccharomyces cerevisiae, which is sensitive to extreme high sugar stress. Most of the DEGs participated in the “glucan synthesis,” “transmembrane transport,” “ribosome,” etc. In this work, we also demonstrated that the gene ZYRO0B03476g (ZrKAR2) encoding Kar2p can significantly affect the growth of Z. rouxii under high sugar stress. In addition, we combined with a previous study on the genome sequence of Z. rouxii, indicating that several gene families contain significantly more gene copies in the Z. rouxii lineage, which involved in tolerance to sugar stress. Our results provide a gene insight for understanding the high sugar tolerance trait, which may impact food and biotechnological industries and improve the osmotolerance in other organisms.

Development of an indirect enzyme-linked immunosorbent assay for the detection of osmotolerant yeast Zygosaccharomyces rouxii in different food

ABSTRACT A polyclonal antibody-based indirect ELISA for the sensitive and specific detection of osmotolerant Zygosaccharomyces rouxii was established. The reactivity of the polyclonal antibodies (pAbs) with Z. rouxii was confirmed by immunofluorescence. The ELISA detection limit was 5 × 104 CFU/mL. For an evaluation of the specificity of pAbs, reactivity to 10 fungi species and 2 bacteria species commonly found in food environments was analysed by indirect ELISA. ELISA reacts with all tested Z. rouxii, whereas no cross-reactions or weakly reactions with 9 fungi and 2 bacteria were observed. The immunoassay staining confirmed the ELISA. Further on, the assay applicability was tested with concentrated apple juice, wine, and honey. Food samples were inoculated with 100 CFU/mL of Z. rouxii. After enrichment for 24 h, the established ELISA can successfully detect contaminated wine and concentrated apple juice samples, while only 30 h was required for honey samples.

Commercial baker's yeast stability as affected by intracellular content of trehalose, dehydration procedure and the physical properties of external matrices.

The effects of vacuum-drying and freeze-drying on the cell viability of a commercial baker's yeast, Saccharomyces cerevisiae, strain with different endogenous contents of trehalose were analyzed. An osmotolerant Zygosaccharomyces rouxii strain was used for comparative purposes. Higher viability values were observed in cells after vacuum-drying than after freeze-drying. Internal concentrations of trehalose in the range 10-20% protected cells in both dehydration processes. Endogenous trehalose concentrations did not affect the water sorption isotherm nor the Tg values. The effect of external matrices of trehalose and maltodextrin was also studied. The addition of external trehalose improved the survival of S. cerevisiae cells containing 5% internal trehalose during dehydration. Maltodextrin (1.8 kDa) failed to protect vacuum-dried samples at 40 degrees C. The major reduction in the viability during the freeze-drying process of the sensitive yeast cells studied was attributed to the freezing step. The suggested protective mechanisms for each particular system are vitrification and the specific interactions of trehalose with membranes and/or proteins. The failure of maltodextrins to protect cells was attributed to the fact that none of the suggested mechanisms of protection could operate in these systems.