Flocculation gene variability in industrial brewer’s yeast strains

Abstract

The brewer's yeast genome encodes a 'Flo' flocculin family responsible for flocculation. Controlled floc formation or flocculation at the end of fermentation is of great importance in the brewing industry since it is a cost-effective and environmental-friendly technique to separate yeast cells from the final beer. FLO genes have the notable capacity to evolve and diverge many times faster than other genes. In actual practice, this genetic variability may directly alter the flocculin structure, which in turn may affect the flocculation onset and/or strength in an uncontrolled manner. Here, 16 ale and lager yeast strains from different breweries, one laboratory Saccharomyces cerevisiae and one reference Saccharomyces pastorianus strain, with divergent flocculation strengths, were selected and screened for characteristic FLO gene sequences. Most of the strains could be distinguished by a typical pattern of these FLO gene markers. The FLO1 and FLO10 markers were only present in five out of the 18 yeast strains, while the FLO9 marker was ubiquitous in all the tested strains. Surprisingly, three strongly flocculating ale yeast strains in this screening also share a typical 'lager' yeast FLO gene marker. Further analysis revealed that a complete Lg-FLO1 allele was present in these ale yeasts. Taken together, this explicit genetic variation between flocculation genes hampers attempts to understand and control the flocculation behavior in industrial brewer's yeasts.

Gravity-Driven Adaptive Evolution of an Industrial Brewer’s Yeast Strain towards a Snowflake Phenotype in a 3D-Printed Mini Tower Fermentor

“…The population at the start, and after seven and fifteen days were compared ( Figure 5). The CMBSVM22 strain possesses the FLO11 gene required for invasive growth [32,[47][48][49], which could clearly be seen on the bottom of the plates. The morphology of the colonies differed after 14 days, the same time when the snowflake flocs were observed.…”

125th Anniversary Review: Yeast Flocculation and Sedimentation in Brewing

“…Studies of ale and lager strains of NewFlo phenotype have revealed that in addition to one or more of the NewFlo type genes, Lg-FLO1, FLONS and FLONL, they possess also FLO genes such as FLO1, FLO5, FLO9 and FLO10 11,99 , which are usually linked to a strong Flo1 phenotype. A priori, it is expected that the Flo1 phenotype (flocculation not inhibited by wort sugars) would be dominant over the Lg-FLO1-encoded NewFlo phenotype (flocculation inhibited by glucose, maltose and maltotriose), so what is the mechanism that gives these yeasts a NewFlo phenotype?…”

“…The genetic background in regard to FLO genes varies greatly among brewer's yeast strains, i.e. different strains contain different combinations of FLO genes 99 , resulting in different flocculation characteristics 69,86 .…”

The mannose-specific lectin domains of Flo1p fromSaccharomyces cerevisiaeand Lg-Flo1p fromS. pastorianus: crystallization and preliminary X-ray diffraction analysis of the adhesin–carbohydrate complexes

“…In this case, a data set was collected to 1.43 Å resolution and the unitcell parameters were a = 45.800, b = 61.770, c = 106.730 Å . The high specificity of the Flo1p lectin domain for mannose and mannosides has previously been determined (Van Mulders et al, 2010;Goossens et al, 2011). Soaking of N-Flo5p crystals in different monosaccharide or oligosaccharide ligand solutions has been reported as a simple, convenient and successful strategy for the structural study of flocculin-carbohydrate complexes (Veelders et al, 2010).…”

“…It was first discovered in the lager yeast S. pastorianus (Kobayashi et al, 1998), but has been found recently also in different ale S. cerevisiae strains (Van Mulders et al, 2010). It is a Flo1p homologue and it is able to confer a 'Newflo' flocculation phenotype, since it is able to interact not only with mannose but also with other sugars such as glucose or maltose.…”