Browsing by Author "Bester, M. C."
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- ItemControlled expression of the dominant flocculation genes FLO1, FLO5, and FLO11 in Saccharomyces cerevisiae(2008) Govender, P.; Domingo, J. L.; Bester, M. C.; Pretorius, I. S.; Bauer, FlorianIn many industrial fermentation processes, the Saccharomyces cerevisiae yeast should ideally meet two partially conflicting demands. During fermentation, a high suspended yeast count is required to maintain a satisfactory rate of fermentation, while at completion, efficient settling is desired to enhance product clarification and recovery. In most fermentation industries, currently used starter cultures do not satisfy this ideal, probably because nonflocculent yeast strains were selected to avoid fermentation problems. In this paper, we assess molecular strategies to optimize the flocculation behavior of S. cerevisiae. For this purpose, the chromosomal copies of three dominant flocculation genes, FLO1, FLO5, and FLO11, of the haploid nonflocculent, noninvasive, and non-flor-forming S. cerevisiae FY23 strain were placed under the transcriptional control of the promoters of the ADH2 and HSP30 genes. All six promoter-gene combinations resulted in specific flocculation behaviors in terms of timing and intensity. The strategy resulted in stable expression patterns providing a platform for the direct comparison and assessment of the specific impact of the expression of individual dominant FLO genes with regard to cell wall characteristics, such as hydrophobicity, biofilm formation, and substrate adhesion properties. The data also clearly demonstrate that the flocculation behavior of yeast strains can be tightly controlled and fine-tuned to satisfy specific industrial requirements. Copyright © 2008, American Society for Microbiology. All Rights Reserved.
- ItemMany Saccharomyces cerevisiae cell wall protein encoding genes are coregulated by Mss11, but cellular adhesion phenotypes appear only Flo protein dependent.(2012) Bester, M. C.; Jacobson, D.; Bauer, Florian
- ItemThe functional dissection of Mss11p, a transcription factor regulating pseudohyphal differentiation, invasive growth and starch metabolism in Saccharomyces cerevisiae.(BLACKWELL PUBLISHING LTD, 9600 GARSINGTON RD, OXFORD, ENGLAND, OXON, OX4 2DG, 2003) Gagiano, M.; Bauer, Florian; Franken, C. J.; Bester, M. C.; Van Dyk, D.; Pretorius, I. S.
- ItemThe regulation of Saccharomyces cerevisiae FLO gene expression and Ca2+-dependent flocculation by Flo8p and Mss11p(2006) Bester, M. C.; Pretorius, I. S.; Bauer, FlorianThe ability of many microorganisms to modify adhesion-related properties of their cell surface is of importance for many processes, including substrate adhesion, cell-cell adhesion, invasive growth, pathogenic behaviour and biofilm formation. In the yeast Saccharomyces cerevisiae, a group of structurally related, cell-wall associated proteins encoded by the FLO gene family are directly responsible for many of the cellular adhesion phenotypes displayed by this organism. Previous research has suggested that the differential transcription of FLO genes determines specific adhesion phenotypes. However, the transcriptional regulation of most FLO genes remains poorly understood. Here we show that the transcriptional activator Mss11p, which has previously been shown to be involved in the regulation of starch degradation, the formation of pseudohyphae and haploid invasive growth, also acts as a strong inducer of flocculation. The data indicate that Mss11p induces flocculation together with Flo8p, and that FLO1 is the dominant target gene of the two factors in this process. The deletion of MSS11 leads to a non-flocculent phenotype, and specific domains of Mss11p that are critical for the induction of flocculation are identified. The data clearly show that several essential transcription factors are shared by at least two flocculation genes that control different adhesion phenotypes. © Springer-Verlag 2006.
- ItemYeast flocculation and its biotechnological relevance(2010) Bauer, Florian; Govender, P.; Bester, M. C.Adhesion properties of microorganisms are crucial for many essential biological processes such as sexual reproduction, tissue or substrate invasion, biofilm formation and others. Most, if not all microbial adhesion phenotypes are controlled by factors such as nutrient availability or the presence of pheromones. One particular form of controlled cellular adhesion that occurs in liquid environments is a process of asexual aggregation of cells which is also referred to as flocculation. This process has been the subject of significant scientific and biotechnological interest because of its relevance for many industrial fermentation processes. Specifically adjusted flocculation properties of industrial microorganisms could indeed lead to significant improvements in the processing of biotechnological fermentation products such as foods, biofuels and industrially produced peptides. This review briefly summarises our current scientific knowledge on the regulation of flocculation-related phenotypes, their importance for different biotechnological industries, and possible future applications for microorganisms with improved flocculation properties. © 2010 Springer-Verlag.