Adaptive Evolution of Industrial Brewer’s Yeast Strains towards a Snowflake Phenotype

Abstract

Flocculation or cell aggregation is a well-appreciated characteristic of industrial brewer’s strains, since it allows removal of the cells from the beer in a cost-efficient and environmentally-friendly manner. However, many industrial strains are non-flocculent and genetic interference to increase the flocculation characteristics are not appreciated by the consumers. We applied adaptive laboratory evolution (ALE) to three non-flocculent, industrial Saccharomyces cerevisiae brewer’s strains using small continuous bioreactors (ministats) to obtain an aggregative phenotype, i.e., the “snowflake” phenotype. These aggregates could increase yeast sedimentation considerably. We evaluated the performance of these evolved strains and their produced flavor during lab scale beer fermentations. The small aggregates did not result in a premature sedimentation during the fermentation and did not result in major flavor changes of the produced beer. These results show that ALE could be used to increase the sedimentation behavior of non-flocculent brewer’s strains.

High Foam Phenotypic Diversity and Variability in Flocculant Gene Observed for Various Yeast Cell Surfaces Present as Industrial Contaminants

“…While expression of the FLO11 gene has been shown to be induced under limiting nutritional conditions [85,86], it will be interesting to analyze the expression of this gene during the fermenting conditions that produce high foaming phenotypes in the different genetic backgrounds of the industrial fuel-ethanol yeast strains analyzed. It is worth noting that yeast strains with flocculating phenotypes can easily appear from non-flocculating yeasts cultures [72,74,77,79,87]. Nevertheless, our results indicate that deleting the primary activator of FLO genes (the FLO8 gene) from the genome of an industrial strain avoids problematic foam formation, flocculation, invasive growth, and biofilm production.…”

Cell Surface Phenotypic Diversity and Flocculation Gene Variability in Contaminant Industrial Fuel-Ethanol Yeast Strains Exhibiting Highly Foaming Phenotypes

“…While expression of the FLO11 gene has been shown to be induced under limiting nutritional conditions [86,87], it will be interesting to analyze the expression of this gene during the fermenting conditions that produce high foaming phenotypes in the different genetic backgrounds of the industrial fuel-ethanol yeast strains analyzed. It is worth noting that yeast strains with flocculating phenotypes can easily appear from non-flocculating yeasts cultures [72,74,77,79,88].…”

Aspects of Multicellularity in Saccharomyces cerevisiae Yeast: A Review of Evolutionary and Physiological Mechanisms

“…Genetically engineered disruption of ACE2 prevents daughter–mother cell separation and can re-create the snowflake phenotype [ 18 , 19 ]. Experimental evolution of the snowflake form was recently successfully applied to industrial beer strains [ 20 ]. Analogous reverse experimental evolution of unicellularity, where only the top fraction from the clumpy strain was transferred to the next generation, confirmed the causative role of the AMN1 gene [ 21 ].…”