Title: Exploring natural and artificial diversity of Saccharomyces cerevisiae for industrial fermentation processes
Other Titles: Exploratie van de natuurlijke en artificiële diversiteit van Saccharomyces cerevisiae voor industriële fermentatieprocessen
Authors: Steensels, Jan
Issue Date: 17-Dec-2014
Abstract: Yeast is the main driving force behind many food fermentation processes, including the production of beer, wine, sake and bread. Historically, these processes originate from uncontrolled, spontaneous fermentation reactions that rely on a complex mixture of microbes present in the environment. Because such spontaneous processes are inherently inconsistent, inefficient and the presence of undesired spoilage microbes regularly leads to the formation of off-flavors, most of today’s industrial production utilizes defined starter cultures, often consisting of a specific domesticated strain of S. cerevisiae, S. bayanus, or S. pastorianus. Although this practice greatly improved process consistency, efficiency, and overall quality, the choice for a particular yeast strain for a specific industrial application is often based on historical, rather than scientific grounds, often resulting in the commercial application of a suboptimal strain. Moreover, new biotechnological yeast applications, such as the production of second-generation biofuels and other biochemicals, or the controlled fermentation of cocoa for the production of chocolate, confront yeast with completely new environments and challenges. Therefore, this study aims to identify or develop novel, superior yeast variants for both new and traditional fermentation processes.In the first chapter, we give a detailed, comprehensive literature overview of the natural biodiversity of Saccharomyces yeasts, describe the history of single-strain yeast starter cultures and discuss several methods to developed artificial yeast variants with altered characteristics. In Chapter 2, we describe the large-scale phenotypic investigation (mainly focusing on stress tolerance, aroma production and fermentation characteristics) of a broad collection of genetically diverse Saccharomyces yeasts originating from various niches. This way, we were able to identify some interesting patterns and correlations, and revealed some systematic differences between natural strains (so-called non-domesticated or wild strains) and strains from synthetic (man-made) fermentation environments (domesticated strains). For example, we were able to show that the production of fruity acetate esters is significantly higher in domesticated compared to natural strains, hinting towards positive selection for this trait during domestication. Moreover, the resulting dataset allowed selection of phenotypically interesting yeast strains directly employable in specific industrial settings, such as the selection of highly osmo- and ethanol-tolerant wine and wild strains for the production of second generation bioethanol. In Chapter 3 and 4, we further use this dataset as a platform to select parental strains for further phenotypic improvement through large-scale breeding programs. In these experiments, we mainly target the yeast’s ability to produce high concentrations of isoamyl acetate (IA), the main responsible for the fruity flavors in fermented foods and beverages. This way, novel hybrid strains were developed for the production of highly aromatic ale beers (Chapter 3). Interestingly, many of these newly developed beer yeasts showed a strong heterosis effect for IA production, while retaining their overall fermentation performance. Additionally, novel hybrid yeasts for the production of specialty chocolate were produced (Chapter 4). These new variants combine beneficial traits from both parental strains: robustness in a cocoa environment and a high production of fruity aroma compounds. In a final chapter, we used Quantitative Trait Locus (QTL) mapping to identify genetic factors underlying the immense differences in IA production observed in S. cerevisiae strains. The genetic mechanisms underlying this complex (but industrially highly relevant) trait are currently insufficiently studied and identification of superior alleles might enable more targeted approaches of strain improvement, such as genetic engineering or marker-assisted breeding.In conclusion, this work provides a global overview of the Saccharomyces phenome (with the main focus on industrially relevant traits) and the exploitation of the resulting dataset for the development of superior yeast variants and the investigation of the genetic factors underlying natural diversity of aroma production.
Publication status: published
KU Leuven publication type: TH
Appears in Collections:Centre of Microbial and Plant Genetics

Files in This Item:
File Status SizeFormat
JanS - PhD thesis (public defense).pdf Published 9402KbAdobe PDFView/Open Request a copy

These files are only available to some KU Leuven Association staff members


All items in Lirias are protected by copyright, with all rights reserved.