The effect of thiamine, biotin, and pyridoxine on the interaction dynamics of wine yeast consortia
Date
2024-12
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Stellenbosch : Stellenbosch University
Abstract
Yeasts are the main driving force behind wine fermentation, and many species are at play in this ecosystem. Non-Saccharomyces yeasts are more abundant in the beginning of the fermentation process, but as fermentations continue, Saccharomyces cerevisiae dominates. S. cerevisiae is well adapted to the harsh fermentation environment and. Adaptations include resistance to general abiotic and biotic fermentation stresses. During fermentation, many microbial species co-exist, and ecological interactions occur. Despite the fact that interactions between yeast-yeast interactions are central to determining wine fermentation outcomes, the mechanisms that mediate these interactions are currently not well understood. Previous studies focused on the transcriptomic responses of S. cerevisiae and non-Saccharomyces species in mixed-species fermentations and have highlighted impacts on biotin-linked carbohydrate metabolic processes and the thiamine biosynthesis pathway, with pyridoxine known to play a role in thiamine synthesis. Vitamins fulfil various functions in yeast metabolism. Thiamine acts as a co-factor in various metabolic pathways, such as the tricarboxylic acid cycle, biotin plays a role in carbohydrate degradation, and pyridoxine acts as a cofactor for enzymes in amino acid metabolism. Past research has focussed on the yeast vitaminic requirements but not much is known about their role in yeast interactions. The aim of this project was, therefore, to determine the role that biotin, pyridoxine, and thiamine play in the interactions between three keystone wine yeast species, S. cerevisiae, Lachancea thermotolerans, and Torulaspora delbrueckii. We evaluated the effects of varied extracellular vitamin concentrations on the growth and fermentation dynamics of synthetic wine-associated yeast consortia in monoculture, in species pairs, and in three-species consortia. Yeast species were co-cultured in Synthetic Grape Must (SGM) in both 6-well plates and 1-L Erlenmeyer flasks, with varying vitamin concentrations to assess the impact on species interactions and growth, monitored through flow cytometry. The results showed that in the absence of exogenous thiamine, T. delbrueckii competed more closely with S. cerevisiae. Both non-Saccharomyces species exhibited significantly reduced growth without exogenous biotin, though this inhibition was mitigated in the presence of S. cerevisiae. Both of these observations were consistent across the small- and large-scale fermentations. S. cerevisiae grew significantly less in monoculture without exogenous pyridoxine, which was not observed in co-culture, in the small-scale fermentations. However, in the large-scale fermentations S. cerevisiae was unaffected by pyridoxine concentration in monoculture, but the absence of pyridoxine greatly stunted its growth in co-culture. This observation likely highlights the impact different oxygen levels and nutrient availability. The findings show that extracellular vitamin concentrations significantly influence yeast growth, but that the impact is dependent on the combination of species, revealing potential mechanisms of indirect interaction in these yeasts.
Description
Thesis (MScAgric)--Stellenbosch University, 2024.