A <em>Saccharomyces cerevisiae</em> wine yeast strain overproducing mannoproteins selected through classical genetic methods

Aims: Developing, by classical genetic methods, new wine yeast strains showing improved release of mannoproteins during wine fermentation, as well as suitable selection procedures for this purpose. These strains would be useful to improve quality characters associated to wine mannoprotein content. Methods and results: UV mutagenesis was used for genetic improvement of the industrial wine yeast strain ADY1. Cell wall-related phenotypes were used as primary selection criteria; an additional screening procedure was developed based on the detection of the released mannoproteins by hybridization with peroxidase-labeled Concanavalin A. Mannoprotein overproduction was assessed in laboratory media as well as in grapevine juice. One mutant strain, renamed HPS, was selected using these criteria. HPS showed increased mannoprotein release in different culture media, including natural must. Moreover, white wines fermented with this improved strain were less susceptible to protein haze than equivalent wines fermented with the original ADY1 strain. Red wines fermented with the mutant strain were also polysaccharide-enriched as compared to the original one. Conclusion: No clear correlation between a specific cell wall-related phenotype, or a combination of them, and improved release of polysaccharides by yeast random mutants could be established, and not all strains identified by in vitro assays as mannoprotein overproducing mutants were found positive for mannoprotein release in industrial conditions. Nevertheless, UV mutagenesis, combined with Concanavalin A detection, seems to be a viable way to improve mannoprotein release by industrial wine yeast strains. Significance and impact of the study: This study is one of the few recent reports on genetic improvement of wine yeast strains by non-recombinant genetic tools. It shows that mannoprotein release can be genetically improved and, for the first time, describes a successful selection procedure for such a complex character. These strains are potentially useful for the improvement of mannoprotein-related characters of white and red wines.