Masters Degrees (Viticulture and Oenology)

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Browsing Masters Degrees (Viticulture and Oenology) by Author "Brown, Mariska"

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    Examining FLO gene expression of Saccharomyces cerevisiae in the presence of selected non-Saccharomyces strains
    (Stellenbosch : Stellenbosch University, 2022-03) Brown, Mariska; Bauer, Florian; Rossouw, Debra; Stellenbosch University. Faculty of Agrisciences. Dept. of Viticulture and Oenology.
    ENGLISH ABSTRACT: The yeast cell wall hosts several protein families, including a group of structurally similar proteins termed Flo (flocculation) proteins. These proteins are responsible for different forms of cell adhesion, including biofilm formation, pseudohyphae formation and flocculation. The FLO genes are genetically very similar, and appear to differ only in their affinity for sugar types and in the amount of adhesion their expression confers. It is still unclear why a group of genetically similar genes, all appearing to contribute to the same phenotype, have been evolutionarily conserved. Recently, it was reported that overexpression of some of these genes in Saccharomyces cerevisiae vastly influences multispecies population dynamics in fermentation conditions. S. cerevisiae appears to dominate the fermentation when certain FLO genes are overexpressed, while overexpression of others can negatively impact the persistence of this species. Additionally, it was found that this species can selectively aggregate with others, depending on the dominant FLO gene expressed. It was thus hypothesised that these genes could play a role in interspecies interaction. And if FLO gene expression influences interspecies interaction, it raised the question whether interspecies interactions have an effect on FLO gene expression. This study sought to determine whether specific FLO genes in S. cerevisiae are expressed at different levels when this yeast is in the presence of different species, specifically Hanseniaspora opuntiae, Lachancea thermotolerans and Wickerhamomyces thermotolerans. RT-qPCR was utilised to measure expression levels during fermentations in synthetic grape must. FLO genes generally experienced an increase in expression in mixed cultures. However, these increased expression levels varied widely between the different co-cultures, as well as over time. These results confirm that FLO genes play an important role in interspecies interaction. Preliminary microscopy results furthermore show that S. cerevisiae indeed demonstrates differential aggregation behaviour based on pure culture or mixed culture with these three species. The study provides a novel approach to FLO gene research, since abiotic rather than biotic factors have mainly been examined in FLO gene expression assays. The data also support the hypotheses that S. cerevisiae has adapted to multispecies systems and that physical contact may have played an important role in interspecies interactions and evolution in complex natural or domesticated ecosystems.