These glycoproteins, which include Flo1p, Flo5p, Flo9p, Flo10p and Flo11p, are termed flocculins or adhesins (reviewed in Verstrepen & Klis, 2006; Dranginis et al., 2007; Bauer et al., 2010). On the basis of their sensitivity to sugar inhibition, three distinct flocculation phenotypes have been characterized, which include Flo1-type

[mannose-sensitive (MS)], NewFlo-type [glucose- and mannose-sensitive (GMS)] and a mannose-insensitive (MI)-type (Masy et al., 1992). Both MS- and GMS-types are Ca2+-dependent flocculation phenotypes that can be attributed to FLO1-, FLO5- and FLO9-overexpression in Saccharomyces cerevisiae strains (Guo et al., 2000; Liu et al., 2007; Govender et al., 2008, 2010; Van Mulders et al., 2009). It should also be noted that Flo11p is required for strong Flo1-type flocculation

in Saccharomyces diastaticus strains (Bayly et al., 2005). In contrast, the MI phenotype displays Ca2+-independent flocculation and is yet to beta-catenin signaling be ascribed to a particular FLO gene. To meet the demands of a consumer-driven market, wine processing currently involves fining and clarification procedures to produce clear and physicochemical stable wines. Wine fining entails the purposeful addition of an adsorptive compound (bentonite, gelatin or albumin), followed by the settling or precipitation (cold stabilization) of partially soluble components from the wine. Further clarification is usually achieved by sedimentation, racking, centrifugation and filtration (Boulton et al., 1996; Rucaparib supplier Ribéreau-Gayon et al., 2000; Pretorius & Bauer, 2002). Moreover, studies have shown that filtration alters the aroma and colour of the wine and also removes molecules that would otherwise positively contribute to the impression of body and volume on the palate (Lubbers et al., 1994; Boulton et al., 1996; Moreno & Azpilicueta, 2004; Moreno et al., 2007). Thus, it may be concluded that the fining and clarification of wine are expensive and time-consuming procedures that ultimately negatively impact on

the cost of the finished product. Efficient wine yeast flocculation after primary alcoholic fermentation leads to the formation of compacted sediments (Lahtchev & Pesheva, 1991) or ‘caked’ lees, thereby reducing the handling of wines and minimizing problems however associated with wine clarification (Pretorius & Bauer, 2002). As such, this ultimately contributes to lower volume loss of the finished wine products. The fact that the natural flocculent ability of certain commercial wine yeast strains is advertised by retailers of active dry wine yeasts further highlights the significance and attractiveness of this trait to the wine industry (http://www.maurivinyeast.com/media/51.pdf, 18 January 2010). Being mindful of this, we showed in a recent study that by placing the native chromosomal copies of two dominant flocculation genes, FLO1 and FLO5 in two nonflocculent commercial S.