Changes

Flocculation is a bimodal process in which a non-flocculent population develops into one comprising of flocculent and non-flocculent cells (Miki et al, 1982). The efficiency of flocculation is determined by the timing of flocculation onset and the rate of flocculation in conjunction with the ratio of flocculent to non-flocculent cells (Stratford and Keenan, 1987; 1988; van Hamersveld et al, 1996). The rate-limiting step is doublet formation, requiring the presence of active surface proteins (Stan and Despa, 2000). The mechanism by which this occurs is thought to be the [[lectin]] interaction theory.

Flocculation is a bimodal process in which a non-flocculent population develops into one comprising of flocculent and non-flocculent cells (Miki et al, 1982). The efficiency of flocculation is determined by the timing of flocculation onset and the rate of flocculation in conjunction with the ratio of flocculent to non-flocculent cells (Stratford and Keenan, 1987; 1988; van Hamersveld et al, 1996). The rate-limiting step is doublet formation, requiring the presence of active surface proteins (Stan and Despa, 2000). The mechanism by which this occurs is thought to be the [[lectin]] interaction theory.

Lectin Interaction Theory

==Lectin Interaction Theory==

The accepted mechanism of flocculation involves a protein-carbohydrate model (Miki et al, 1982) (figure 1.3). Fully flocculent yeast cells exhibit carbohydrate α-mannan receptors and protein lectins (section 1.5.4). It has been suggested that lectin like interactions between the two results in the flocculation phenotype (section 4.1) with Ca2+ ions required for the correct conformation of the flocculation lectins. Coflocculation between Kluyveromyces and Schizosaccharomyces has been shown to be by a “lectinic” mechanism (El-Behhari et al, 2000). This theory explains the essential role of calcium and how deproteinisation affects flocculation.

The accepted mechanism of flocculation involves a protein-carbohydrate model (Miki et al, 1982) (figure 1.3). Fully flocculent yeast cells exhibit carbohydrate α-mannan receptors and protein lectins (section 1.5.4). It has been suggested that lectin like interactions between the two results in the flocculation phenotype (section 4.1) with Ca²⁺ ions required for the correct conformation of the flocculation lectins. Coflocculation between Kluyveromyces and Schizosaccharomyces has been shown to be by a “lectinic” mechanism (El-Behhari et al, 2000). This theory explains the essential role of calcium and how deproteinisation affects flocculation.

   

   

Flocculation Lectins and Phenotypes

==Flocculation Lectins and Phenotypes==

Three flocculation phenotypes have been elucidated based on the lectins they produce: Flo1 (Stratford and Assinder, 1991) NewFlo (Stratford and Assinder, 1991) and Mannose Insensitive (MI) (Masy et al, 1992; Dengis and Rouxhet, 1997). These flocculation phenotypes differ in the time of the onset of flocculation and the sugar inhibition of flocculation. Flocculation has also been classified according to time of onset and floc morphology.

Three flocculation phenotypes have been elucidated based on the lectins they produce: Flo1 (Stratford and Assinder, 1991) NewFlo (Stratford and Assinder, 1991) and Mannose Insensitive (MI) (Masy et al, 1992; Dengis and Rouxhet, 1997). These flocculation phenotypes differ in the time of the onset of flocculation and the sugar inhibition of flocculation. Flocculation has also been classified according to time of onset and floc morphology.

The genetic control of yeast flocculation has not been extensively studied. Recent reports suggest genes encoding lectin-like proteins exhibit close sequence homology (Jin and Speers, 1991, 1999; Smart, 2001). Furthermore it seems that FLO genes have interchangeable functions that can compensate for one another (Guo et al, 2000).

The genetic control of yeast flocculation has not been extensively studied. Recent reports suggest genes encoding lectin-like proteins exhibit close sequence homology (Jin and Speers, 1991, 1999; Smart, 2001). Furthermore it seems that FLO genes have interchangeable functions that can compensate for one another (Guo et al, 2000).

Flocculation Phenotypes

==Flocculation Phenotypes==

The Flo1 phenotype is inhibited by mannose (Burns, 1937; Miki et al, 1982; Nishihara and Toraya, 1987; Kihn et al, 1988; Stratford, 1989; Stratford and Assinder, 1991) occurs in both ale and lager strains (Miki, 1982; Stratford and Assinder, 1991; Masy et al, 1992; Smit et al, 1982; Stratford, 1993; Stratford and Carter, 1993; Teunissen et al, 1993; Teunissen et al, 1995a, b; Bony et al, 1997; Braley and Chaffin, 1999; Fleming and Pennings, 2001; He et al, 2002; Verstrepen et al, 2003) and is associated with the FLO1 gene (Watari, 1991 Masy et al, 1992; Stratford, 1993; Stratford and Carter, 1993; Teunissen et al, 1993; Teunissen et al, 1995a, b; Bony et al, 1997; Braley and Chaffin, 1999).  

The Flo1 phenotype is inhibited by mannose (Burns, 1937; Miki et al, 1982; Nishihara and Toraya, 1987; Kihn et al, 1988; Stratford, 1989; Stratford and Assinder, 1991) occurs in both ale and lager strains (Miki, 1982; Stratford and Assinder, 1991; Masy et al, 1992; Smit et al, 1982; Stratford, 1993; Stratford and Carter, 1993; Teunissen et al, 1993; Teunissen et al, 1995a, b; Bony et al, 1997; Braley and Chaffin, 1999; Fleming and Pennings, 2001; He et al, 2002; Verstrepen et al, 2003) and is associated with the FLO1 gene (Watari, 1991 Masy et al, 1992; Stratford, 1993; Stratford and Carter, 1993; Teunissen et al, 1993; Teunissen et al, 1995a, b; Bony et al, 1997; Braley and Chaffin, 1999).