A new methodology to obtain wine yeast strains overproducing mannoproteins

Abstract

Yeast mannoproteins are highly glycosylated proteins that are covalently bound to the β-1,3-glucan present in the yeast cell wall. These complex macromolecules are structurally composed of polymers of sugars, mainly mannose, that are covalently linked to peptides and represent around 40% of the cell wall dry weight. Yeast mannoproteins contribute to several aspects of wine quality by protecting against protein haze, reducing astringency, retaining aroma and other undesired compounds such as OTA and stimulating the growth of lactic-acid bacteria. Therefore, the development of a non-recombinant method to obtain enological yeast strains overproducing mannoproteins would be very useful. Previous works developed in our group have allowed the identification of several genetic determinants for the release of wine yeast mannoproteins (Gonzalez-Ramos and Gonzalez, 2006; Gonzalez-Ramos et al., 2008). Among the different recombinant genotypes constructed and studied, strains deleted for KNR4 (from Killer Nine Resistant, also known as SMI1), a gene involved in β-1,3-glucan biosynthesis yielded optimal results (Gonzalez-Ramos et al., 2008). In the present paper, a new methodology for the selection of non-recombinant mannoprotein overproducing yeast strains based on their resistance to the killer 9 toxin of Williopsis saturnus is developed.