MECHANISM OF PHENOTYPIC VARIATIONS IN THE FLOCCULENCE CHARACTER OF YEAST

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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.