Saccharomyces cerevisiae EC1118

Industrial S. cerevisiae wine yeast: derived from a double selection process, environmental and human

The industrial Saccharomyces cerevisiae wine yeasts have been selected from spontaneous fermentations for specific technological properties. During fermentation of the grape must, the yeast are exposed to high concentrations of sugar (180-260 g/L), high levels of ethanol, low pH, the presence of sulfites, and limiting quantities of nitrogen, lipids and vitamins, under strong anaerobic conditions. When confronted with this hostile environment, wine yeasts present properties which clearly distinguish them from laboratory strains. Specifically, they exhibit good fermentative performances, good resistance to ethanol, reduced production of undesirable compounds (acetate, H2S) and production of stable quantities of aromatic compounds (esters, higher alcohols, carbonyl compounds and sulfur compounds). The characteristics of wine yeast strains are also different from those of the natural populations of S. cerevisiae from which they were isolated. The very specific properties of industrial wine yeast strains result from both a strong selective pressure by the oenologic environment and a screening by human selection for selection of the requisite characteristics from hundreds or even thousands of strains.

Importance of sequencing the genome of S. cerevisiae EC1118

Whereas the phenotypic characteristics of wine yeast strains have been well-documented, the genetic origin of these specific properties remains to be identified. Various mechanisms participate in the adaptation of oenologic strains to their environment, such as polyploidy, aneuploidy and chromosome translocations (Rachidi et al., 1999; Perez-Ortin et al., 2002; Infante et al., 2003). The analysis of several genomes from wine yeast by CGH (Comparative Genomic Hybridization) has recently shown that certain genes have been amplified and others are absent (Dunn et al., 2005). Besides structural modifications, it is expected that sequence polymorphisms play a major role in the observed properties. The divergence between S288C and RM11 is estimated at 0.5-1%, close to that observed between humans and chimpanzees (broad.mit.edu).

The study of the EC1118 genome, and notably a detailed comparison with other strains of S. cerevisiae which have been sequenced (S288C and RM11) will make it possible to identify the genetic characteristics of these strains at the level of genome organization (heterozygosity, rearrangements, new/absent genes, chimerical genes, etc.) and to determine the ensemble of sequence variations which are specific to this strain. The availability of this sequence will be essential for the identification of the genetic bases for the differences in properties between oenologic strains and other strains of S. cerevisiae (laboratory strains as well as natural isolates). The sequence of EC1118 will also contribute to the analysis of intra-specific biodiversity and will foster reflection on the molecular mechanisms implicated in the dynamics of genomes and their evolution within the S. cerevisiae species.

Importance of EC1118 as a model for the study of genotype-phenotype relationships

EC1118 is a commercial strain which is one of the most utilized strains in the world. It is a strain which is very well known physiologically and its technological properties have been widely studied. The expression of the genome of EC1118 has been analysed at the transcriptomic and proteomic level under different physiological conditions, including the fermentation process (data are available at: http://bioweb.ensam.inra.fr/yet/). The comparative transcriptomic analysis of EC1118 and S288C has revealed numerous differences in expression.

The availability of a high quality sequence offers new perspectives for global studies integrating different levels of information which will make it possible to relate the sequence variations to expression and metabolic variations, in order to understand genotype-phenotype relationships. These studies should lead to key knowledge about the molecular basis of variations in expression in these industrial strains and their contribution to the properties of the strains. The knowledge produced about the nature of the affected genes and about the molecular mechanisms implicated, should lead to a new vision of the modalities of adaptation of industrial yeasts to difficult environmental conditions. From an industrial point of view, the identification of key genes for the properties of strains will lead to a better exploitation of biodiversity. This knowledge should also offer new perspectives in terms of amelioration of strains.