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Rafael Alvarez défendra sa thèse intitulée 'Genetic basis of oenological traits in interspecific Saccharomyces hybrids', lundi 19 juin 2023 devant le jury composé de :

• Rapporteur : M. Florian F. BAUER, Université Stellenbosch, Afrique du Sud
• Rapporteure : Mme Daniela DELNERI, Université de Manchester, Royaume-Uni
• Examinateur : M. Philippe MARULLO, ISVV, Université de Bordeaux, Biolaffort
• Examinatrice : Mme Kayoko TANAKA (examinatrice), Université de Leicester, Royaume-Uni
• Invitée : Mme Fabienne REMIZE, Professeur Université Montpellier, UMR SPO

 
Résumé :
Wine fermentation has long been conducted by using Saccharomyces cerevisiae. This species is the workhorse of beer, wine, cider and sake production all around the globe, as a pure species or, to a lesser extent, as a part of interspecific hybrids with other Saccharomyces species. However, other Saccharomyces species have shown a high potential to diversify the organoleptic properties of wine and tackle the environmental challenges that the wine industry has been facing in recent years.
In this work, we phenotyped 92 yeast strains belonging to all the current Saccharomyces species in synthetic grape must fermentation. Our results showed that contrary to the expected, all Saccharomyces species can ferment efficiently under the conditions used. Remarkably, strains of S. kudriavzevii, S. arboricola and interspecific Sc x Sk hybrids fermented more efficiently than wine S. cerevisiae strains. Regarding metabolite production, we observed a high intraspecies variability for some species. Even more interestingly, we observed specificities at the species level: some non-cerevisiae Saccharomyces produced high amounts of industrially relevant compounds such as glycerol, succinate and fermentative aromas, or extremely low amounts of acetic acid, compared to S. cerevisiae. Overall, the potential of alternative Saccharomyces was higher than expected. They constitute a promising alternative to diversify the current set of commercially available yeast strains, either as pure species or following interspecific hybridisation.
Interspecific Saccharomyces hybrids can be easily obtained in the lab thanks to the weak pre-zygotic barriers in this genus. Although viable, those hybrids are sterile, as the high genetic divergence between homologous chromosomes prevents their correct segregation during meiosis. However, allotetraploid hybrids are fertile, as recombination in these organisms occurs between chromosomes of the same species, minimising sequence divergence and facilitating a correct segregation during sporulation. We used this phenomenon to construct a a fertile S. uvarum x S. mikatae hybrid and performed QTL mapping for the first time in non-cerevisiae Saccharomyces species. We found several genomic regions in the S. uvarum subgenome affecting the production of central carbon metabolites and, to a lesser degree, fermentative aromas and kinetic parameters. Verifying some of the candidate genes will shortly provide new tools for improving S. uvarum and its hybrids in a winemaking context.
Overall, this study uncovered the potential of non-cerevisiae Saccharomyces species to tackle the current challenges of the wine industry and provided the first QTL mapping study of species other than S. cerevisiae in a winemaking context, laying the first stone of a promising area in the field of wine microbiology.

Ce travail a été réalisé sous la direction de Sylvie DEQUIN (INRAE, UMR SPO), Carole CAMARA (INRAE, UMR SPO) et Ed Louis (Université de Leicester, UK).

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Contact : Carole Camarasa (INRAE, UMR SPO)