Flocculation in industrial strains ofSaccharomyces cerevisiae: role of cell wall polysaccharides and lectin-like receptors

Abstract

Yeast flocculation is the reversible aggregation of yeast cells promoted by the interaction between lectin‐like protein receptors with mannose side chains on adjacent cell walls. Flocculation is governed by several physiological factors, including the type of nutrient sugar available to yeast. We grew four industrial strains of Saccharomyces cerevisiae, representing applications in the brewing, winemaking and bioethanol sectors, to late stationary phase and quantified the cellular content of mannans, glucans and lectin‐like proteins on yeast cell surfaces. Results indicated that brewing and champagne strains showed moderate to high flocculation ability when grown with glucose, fructose, maltose or galactose, whereas winemaking and fuel alcohol strains only showed moderate flocculation when grown on maltose and galactose. All yeast strains studied were weakly flocculent when grown on mannose. With regard to lectin‐like receptors, their number played a more important role in governing yeast flocculation than the mannan and glucan contents in yeast cell walls. We conclude that all the industrial strains of S. cerevisiae belonged to New‐Flo type on the basis of their flocculation behaviour observed when cultured on different sugars. Quantification of yeast cell wall polysaccharides and receptor sites indicates that mannan and glucan levels remain almost constant, irrespective of the strain under investigation. The main difference in flocculation characteristics in industrial yeast strains appears to be due to variations in concentrations of lectin‐like cell surface receptors. Our findings may benefit brewers, winemakers and other yeast‐based technologies in design of media to prevent premature flocculation during fermentation. Copyright © 2017 The Institute of Brewing & Distilling

Consolidated bioprocessing of corn cob-derived hemicellulose: engineered industrialSaccharomyces cerevisiaeas efficient whole cell biocatalysts

“…secretory capacity [18], cell wall composition [25,26], expression levels of host-cell genes [27]. Furthermore, yeast cell size is another source of variability, as larger cells have a lower total superficial cell area available for enzyme display per unit biomass.…”

“…1) were not the ones presenting higher XYLA and XYN activity values (Table S1 [see Additional file 1]), supporting the necessity of making the selection of appropriate yeast strain backgrounds in process-like conditions. Another factor to be taken into consideration is the flocculation ability, a process that is mediated by lectin-like receptors present in the cell surface which bind mannose residues in adjacent cells creating clusters of thousands of cells [28], but have also been reported to bind to a wide range of sugars [25].…”

Consolidated bioprocessing of corn cob-derived hemicellulose: engineered industrial Saccharomyces cerevisiae as efficient whole cell biocatalysts

“…1) were not the ones presenting higher XYLA and XYN activity values (see Additional file 1: Table S1), supporting the necessity of making the selection of appropriate yeast strain backgrounds in process-like conditions. Another factor to be taken into consideration is the flocculation ability, a process that is mediated by lectin-like receptors present in the cell surface which bind mannose residues in adjacent cells creating clusters of thousands of cells [28], but have also been reported to bind to a wide range of sugars [25]. Accordingly, the CA11 strain, being a flocculant strain, will present an high number of lectin-like receptors in the cell surface [25], that may potentiate the binding of the yeast to sugar residues in xylan/XOS, and benefit the hydrolysis in the long term due to substrate proximity.…”

“…Another factor to be taken into consideration is the flocculation ability, a process that is mediated by lectin-like receptors present in the cell surface which bind mannose residues in adjacent cells creating clusters of thousands of cells [28], but have also been reported to bind to a wide range of sugars [25]. Accordingly, the CA11 strain, being a flocculant strain, will present an high number of lectin-like receptors in the cell surface [25], that may potentiate the binding of the yeast to sugar residues in xylan/XOS, and benefit the hydrolysis in the long term due to substrate proximity. Furthermore, different predisposition to convert xylose into xylitol, normally observed between S. cerevisiae strains [16], may alleviate product inhibition of xylanase and xylosidase by xylose, increasing the overall degradation of xylan.…”

Genome sequencing, assembly, and annotation of the self-flocculating microalga Scenedesmus obliquus AS-6-11

“…Yeast cell occulation has been widely used in the beer industry and biofuels production as a simple, economic and environmentally friendly way to harvest cells [35][36]. The interaction of lectin-like receptors with adjacent mannose side chains in cell walls played a vital role in yeast occulation [37]. In addition to lectin-glycan interaction, glycan-glycan interactions also act a pivotal part in cell-cell adhesion, and the occulation mechanism contributes to the self-interaction of Flo proteins in the coordination of Ca 2+ [38].…”