Author:

Abstract:

The main fundamental research topic at the Laboratory of Molecular Cell Biology (KULeuven) and Department of Molecular Microbiology (VIB) is nutrient-induced signal transduction in the yeast Saccharomyces cerevisiae. In recent years, several applied research lines have been derived thereof and an extensive collaboration with several companies employing yeast has been established. The major interest of the past and ongoing projects is the development of yeast strains with a better performance when used in specific applications in the baker’s, brewer’s and wine yeast industry. In the course of their production and usage, industrial yeast strains are exposed to a plethora of sequential and simultaneous stress conditions and their performance highly depends on the extent to which they are capable of coping with these conditions. We have developed yeast strains that are better suited for use in frozen doughs and ‘high gravity brewing’, two increasingly important developments in the baker’s and brewer’s yeast industry, respectively. In addition, we have isolated and characterized mutant strains which are less vulnerable to so-called sluggish or stuck fermentations in wine making. The mutants showing the best characteristics in laboratory conditions are passed to our industrial partners for further testing in pilot and finally industrial scale. All these types of mutants have been isolated directly in an industrial strain background using UV mutagenesis followed by an adequate selection approach. The latter has proven to be a very challenging but important step, given the discrepancy between laboratory and industrial conditions. Moreover, the mutants should not be affected negatively in other important commercial characteristics next to the positive improvement envisaged. Since not all industrially-relevant phenotypes can be selected by direct gain-of-function selection, we are currently isolating strain variants via the so-called ‘directed evolution’ or ‘evolutionary engineering’ in chemostat cultures. In this approach, random variation is induced and subsequent adaptations to novel environments identified in a continuous, long-term process. This type of selection procedure better reflects process-relevant conditions and cannot lead to highly specialized but cripple strains. From a scientific point of view, the genetic basis of the improved phenotype of the isolated strains is intriguing since they are all diploid or tetraploid. It is important to realize, however, that most commercially-relevant properties of yeast cells are polygenic and thus hard to study. Currently, the genetic basic of such properties is investigated by analyzing the possible contribution of candidate genes individually. We are now developing a novel and powerful technology for the simultaneous identification of all genes involved in a polygenic property. The new method will allow the precise identification of all genetic elements responsible for a specific commercially-important trait in industrially used strains.