Yeast flocculation: understanding cell surface structure-function relationships in industrial yeast strains
Adhesion properties of microorganisms are crucial for many essential biological processes such as sexual reproduction, tissue or substrate invasion, biofilm formation and cell-cell aggregation. One of such controlled forms of cellular adhesion in yeast that occurs preferentially in the liquid environments is a process of asexual aggregation of cells which is also referred to as flocculation. The timing during growth and the causes of onset of yeast flocculation are of commercial interest to the brewing industry, as flocculation can determine the degree of attenuation of the wort. Early or premature flocculation is one common causes of ‘hung’ or ‘stuck’ fermentations giving rise to sweeter beer whereas a lack or delay in flocculation can cause filtration difficulties and some problems in obtaining a bright sparkling beer; in addition, the presence of excess yeast in beer during ageing can cause off flavours due to yeast autolysis. Despite this commercial interest, limited information is available about the onset of flocculation and the various factors that may be responsible in the process. In particular, what are the signals that trigger flocculation? Adhesion properties applicable in improving yeast biotechnology are dependent directly or indirectly on characteristics of cellular surfaces, usually the outer layer of the cell wall. Change in the structure and or composition of the cell wall leads to changes in the microbial adhesion properties. Exploring more into the cell wall and studying the nanoscale structure of the yeast cell wall would thus be beneficial to augment our understanding of flocculation.
Networked Digital Library of Theses and Dissertations