Browsing by Author "Setati, Mathabatha Evodia"
Now showing 1 - 5 of 5
Results Per Page
- ItemCo-flocculation of yeast species, a new mechanism to govern population dynamics in microbial ecosystems(Public Library of Science, 2015) Rossouw, D.; Bagheri, Bahareh; Setati, Mathabatha Evodia; Bauer, FlorianFlocculation has primarily been studied as an important technological property of Saccharomyces cerevisiae yeast strains in fermentation processes such as brewing and winemaking. These studies have led to the identification of a group of closely related genes, referred to as the FLO gene family, which controls the flocculation phenotype. All naturally occurring S. cerevisiae strains assessed thus far possess at least four independent copies of structurally similar FLO genes, namely FLO1, FLO5, FLO9 and FLO10. The genes appear to differ primarily by the degree of flocculation induced by their expression. However, the reason for the existence of a large family of very similar genes, all involved in the same phenotype, has remained unclear. In natural ecosystems, and in wine production, S. cerevisiae growth together and competes with a large number of other Saccharomyces and many more non-Saccharomyces yeast species. Our data show that many strains of such wine-related non-Saccharomyces species, some of which have recently attracted significant biotechnological interest as they contribute positively to fermentation and wine character, were able to flocculate efficiently. The data also show that both flocculent and non-flocculent S. cerevisiae strains formed mixed species flocs (a process hereafter referred to as co-flocculation) with some of these non-Saccharomyces yeasts. This ability of yeast strains to impact flocculation behaviour of other species in mixed inocula has not been described previously. Further investigation into the genetic regulation of co-flocculation revealed that different FLO genes impact differently on such adhesion phenotypes, favouring adhesion with some species while excluding other species from such mixed flocs. The data therefore strongly suggest that FLO genes govern the selective association of S. cerevisiae with specific species of non-Saccharomyces yeasts, and may therefore be drivers of ecosystem organisational patterns. Our data provide, for the first time, insights into the role of the FLO gene family beyond intraspecies cellular association, and suggest a wider evolutionary role for the FLO genes. Such a role would explain the evolutionary persistence of a large multigene family of genes with apparently similar function.
- ItemEcological interactions are a primary driver of population dynamics in wine yeast microbiota during fermentation(Nature Research (part of Springer Nature), 2020) Bagheri, Bahareh; Bauer, Florian; Cardinali, Gianluigi; Setati, Mathabatha EvodiaSpontaneous wine fermentation is characterized by yeast population evolution, modulated by complex physical and metabolic interactions amongst various species. The contribution of any given species to the final wine character and aroma will depend on its numerical persistence during the fermentation process. Studies have primarily evaluated the effect of physical and chemical factors such as osmotic pressure, pH, temperature and nutrient availability on mono- or mixed-cultures comprising 2–3 species, but information about how interspecies ecological interactions in the wine fermentation ecosystem contribute to population dynamics remains scant. Therefore, in the current study, the effect of temperature and sulphur dioxide (SO2) on the dynamics of a multi-species yeast consortium was evaluated in three different matrices including synthetic grape juice, Chenin blanc and Grechetto bianco. The population dynamics were affected by temperature and SO2, reflecting differences in stress resistance and habitat preferences of the different species and influencing the production of most volatile aroma compounds. Evidently at 15 °C and in the absence of SO2 non-Saccharomyces species were dominant, whereas at 25 °C and when 30 mg/L SO2 was added S. cerevisiae dominated. Population growth followed similar patterns in the three matrices independently of the conditions. The data show that fermentation stresses lead to an individual response of each species, but that this response is strongly influenced by the interactions between species within the ecosystem. Thus, our data suggest that ecological interactions, and not only physico-chemical conditions, are a dominant factor in determining the contribution of individual species to the outcome of the fermentation.
- ItemHeterologous production of family 5 fungal endo-1,4-B-mannanases in Saccharomyces cerevisiae(Stellenbosch : Stellenbosch University, 2002-12) Setati, Mathabatha Evodia; Van Zyl, Willem Heber; Stalbrand, H.; Stellenbosch University. Faculty of Science. Dept. of Microbiology.ENGLISH ABSTRACT: Mannan polysaccharides occur in the hemicellulose fraction of plant cell walls, either as structural polymers or as reserve carbohydrates. They are found predominantly in the seeds of leguminous plants in the form of galactomannan, and in softwoods as galactoglucomannan. Endo-I,4-I3-mannanases hydrolyze mannan polysaccharides to oligosaccharides of various lengths. These enzymes are secreted as single catalytic modules or as part of multi-modular proteins by fungi, bacteria, plants and animals. For example, the l3-mannanase of Aspergillus aculeatus, designated Aa-Man5A, is secreted as a single catalytic module, whereas that of Trichoderma reesei, designated Tr-Man5A, contains a l3-mannanase catalytic module linked to a cellulose-binding module by a Pro- Ser-Thr-rich linker. Heterologous gene expression in yeast provides the opportunity to produce individual hydrolytic enzymes in a host expression system devoid of related activities. Saccharomyces cerevisiae has a well-developed expression system and has frequently been used as a model organism for heterologous gene expression. A number of autoselection systems have been devised so that recombinant S. cerevisiae strains can be cultivated in any medium of choice without exerting selective pressure. An autoselection system based on defective chromosomal ura3 andfurl genes involved in the pyrimidine biosynthesis pathway of S. cerevisiae, and complementation of the ura3 gene with a multicopy plasmid-borne URA3 gene, were used in this study. The man1 of A. aculeatus gene encoding Aa-Man5A was cloned and expressed in autoselective S. cerevisiae under the regulation of the alcohol dehydrogenase (ADH2PT) and the phosphoglycerate kinase (PGK1PT) promoter and terminator sequences. Expression of man1 under both promoters resulted in high production levels of Aa- Man5A. The production levels were significantly higher than the levels of endo-l,4-13- mannanases produced by heterologous expression in Escherichia coli, and were comparable to the production levels of enzymes produced in Pichia pastoris, which presumably has a higher secretion capacity than S. cerevisiae. The recombinant yeast strain expressing man1 under the regulation of the PGK1p promoter displayed stunted biomass formation during the logarithmic phase, which was relieved when the native f3- mannanase secretion signal was replaced with the yeast MFuis secretion signal. The recombinant Aa-Man5A displayed biochemical properties similar to those of the native Aa-Man5A. The recombinant enzyme hydrolyzed unsubstituted mannan to predominantly mannose, mannobiose, and mannotriose. The expression of the man1 and man1 ácbd gene constructs of T reesei in S. cerevisiae fur 1::LEU2 strains under the regulation of the PGK1 PT promoter and terminator resulted in the production and secretion of Tr-Man5A and Tr-Man5A~CBD (lacking the cellulose binding module), respectively. However, the production levels of both proteins were approximately I5-fold lower than the production levels of Aa-Man5A. These levels did not improve after replacement of the native secretion signal with the MFuis secretion signal. Interestingly, reducing the cultivation temperature from 30°C to 20°C led to a five-fold increase in the secreted levels of Tr-Man5A, but a three-fold decrease in the production of Aa-Man5A. A preliminary investigation was performed to evaluate the possibility of using the recombinant Aa-Man5A in the processing of instant coffee. Arabica coffee extracts treated with Aa-Man5A displayed low viscosity in comparison to the untreated extract and showed better retention of volatile/aromatic compounds than the autoclaved extract. The results indicated that Aa-Man5A is capable of hydrolyzing coffee galactomannan and can be used for processing instant coffee.
- ItemInvestigating the effect of selected non-saccharomyces species on wine ecosystem function and major volatiles(Frontiers Media, 2018-11-13) Bagheri, Bahareh; Zambelli, Paolo; Vigentini, Ileana; Bauer, Florian; Setati, Mathabatha Evodia; Cao, MingfengNatural alcoholic fermentation is initiated by a diverse population of several non-Saccharomyces yeast species. However, most of the species progressively die off, leaving only a few strongly fermentative species, mainly Saccharomyces cerevisiae. The relative performance of each yeast species is dependent on its fermentation capacity, initial cell density, ecological interactions as well as tolerance to environmental factors. However, the fundamental rules underlying the working of the wine ecosystem are not fully understood. Here we use variation in cell density as a tool to evaluate the impact of individual non-Saccharomyces wine yeast species on fermentation kinetics and population dynamics of a multi-species yeast consortium in synthetic grape juice fermentation. Furthermore, the impact of individual species on aromatic properties of wine was investigated, using Gas Chromatography-Flame Ionization Detector. Fermentation kinetics was affected by the inoculation treatment. The results show that some non-Saccharomyces species support or inhibit the growth of other non-Saccharomyces species in the multi-species consortium. Overall, the fermentation inoculated with a high cell density of Starmerella bacillaris displayed the fastest fermentation kinetics while fermentation inoculated with Hanseniaspora vineae showed the slowest kinetics. The production of major volatiles was strongly affected by the treatments, and the aromatic signature could in some cases be linked to specific non-Saccharomyces species. In particular, Wickerhamomyces anomalus at high cell density contributed to elevated levels of 2-Phenylethan-1-ol whereas Starm. bacillaris at high cell density resulted in the high production of 2-methylpropanoic acid and 3-Hydroxybutanone. The data revealed possible direct and indirect influences of individual non-Saccharomyces species within a complex consortium, on wine chemical composition.
- ItemThe vineyard yeast microbiome, a mixed model microbial map(PLoS, 2012-12-26) Setati, Mathabatha Evodia; Jacobson, Daniel; Andong, Ursula-Claire; Bauer, FlorianVineyards harbour a wide variety of microorganisms that play a pivotal role in pre- and post-harvest grape quality and will contribute significantly to the final aromatic properties of wine. The aim of the current study was to investigate the spatial distribution of microbial communities within and between individual vineyard management units. For the first time in such a study, we applied the Theory of Sampling (TOS) to sample gapes from adjacent and well established commercial vineyards within the same terroir unit and from several sampling points within each individual vineyard. Cultivation-based and molecular data sets were generated to capture the spatial heterogeneity in microbial populations within and between vineyards and analysed with novel mixed-model networks, which combine sample correlations and microbial community distribution probabilities. The data demonstrate that farming systems have a significant impact on fungal diversity but more importantly that there is significant species heterogeneity between samples in the same vineyard. Cultivation-based methods confirmed that while the same oxidative yeast species dominated in all vineyards, the least treated vineyard displayed significantly higher species richness, including many yeasts with biocontrol potential. The cultivatable yeast population was not fully representative of the more complex populations seen with molecular methods, and only the molecular data allowed discrimination amongst farming practices with multivariate and network analysis methods. Importantly, yeast species distribution is subject to significant intra-vineyard spatial fluctuations and the frequently reported heterogeneity of tank samples of grapes harvested from single vineyards at the same stage of ripeness might therefore, at least in part, be due to the differing microbiota in different sections of the vineyard.