Mechanism of Phenotypic Variations in the Flocculence Character of Yeast

Abstract

The protein and polysaccharide composition of the yeast cell wall has been examined, with the aim of explaining phenotypic variations in the flocculence character which occur during fermentation. The results show that the period of deflocculation coincides with a synthesis of mannan. Accordingly, this polysaccharide appears to act as a regulator of the intensity of flocculation by masking more or less completely the active groups of the specific fraction carrying the flocculence character. Comparative study of a flocculent and a powdery yeast in presence of 2,4‐dinitrophenol showed that the flocculent yeast possessed an intracellular biochemical mechanism—probably under genetic control—which allowed rapid utilization of mannan. From this point of view, the powdery yeast could be considered as a flocculent yeast in a permanent state of deflocculation. Chromatographic analysis of protein hydrolysates from the walls of cells gathered at the end of fermentation were characterized by an increase of 30–40% of total amino acids, without there being any important fluctuations between the proportions of individual amino acids. Taking into account the parallel decrease in mannan content at the end of fermentation, it may be concluded that it is essentially the ratio of mannan to protein which determines the physiological state of the cell.

Yeast Flocculation: Influence of Nutritional Factors on Cell Wall Composition

“…According to Masschelein et al (1963), the mannoproteins of yeast walls play a fundamental role in flocculation, the walls of flocculent strains having more mannans than those of nonflocculent strains. However, this view was criticized by Griffin & MacWilliam (1969), who failed to demonstrate any differences in the amounts of these polymers between flocculent and non-flocculent yeasts.…”

“…We showed that flocculation of these two strains was controlled by the Ca2+/K+ ratio in the medium. The chemical composition of the yeast cell wall changes during the development of the yeast (Bonaly et al, 1971) and flocculation phenomena depend directly on the components of the wall (Masschelein et al, 1963). The nature of these cell wall components and the effect that they have are the subject of contrasting theories concerning the phenomenon of yeast flocculation (Lyons & Hough, 1970, 1971Griffin & MacWilliam, 1969;Mill, 1966).…”

Yeast flocculation: Flocculation onset and receptor availability

“…But it is at present unknown whether flocculation onset is There are several pieces of evidence tending to suggest involvement of mannan receptors in flocculation onset. Cell-wall mannan content was originally implicated in flocculation some 30 years ago (Devreux, 1962;Masschelein et al, 1963;Windisch, 1968). Flocculent cell-walls of S. cerevisiae have been shown to contain more mannan (Stewart and Garrison, 1972;Stewart, 1975), as has also been reported in Kluyveromyces bulgaricus (Al-Mahmood et al, 1987) and Pichia pastoris (Mbawala et al, 1990).…”

Variations of two pools of glycogen and carbohydrate in Saccharomyces cerevisiae grown with various ethanol concentrations

“…The content of acid-soluble glycogen is correlated with the process of yeast flocculation [15]. Glycogen content is found to be higher in flocculant yeast strains than in powdery varieties [16]. In yeast, presence of glycogen in the form of a-glucans at cell-surface level of yeast and its role in flocculation are confirmed by using amyloglucosidase treatment.…”