High Complexity and Degree of Genetic Variation in Brettanomyces bruxellensis Population.

Genome-wide characterization of genetic variants of a large population of individuals within the same species is essential to have a deeper insight into its evolutionary history as well as the genotype-phenotype relationship. Population genomic surveys have been performed in multiple yeast species, including the two model organisms, Saccharomyces cerevisiae and Schizosaccharomyces pombe. In this context, we sought to characterize at the population level the Brettanomyces bruxellensis yeast species, which is a major cause of wine spoilage and can contribute to the specific flavor profile of some Belgium beers. We have completely sequenced the genome of 53 B. bruxellensis strains isolated worldwide. The annotation of the reference genome allowed us to define the gene content of this species. As previously suggested, our genomic data clearly highlighted that genetic diversity variation is related to ploidy level, which is variable in the B. bruxellensis species. Genomes are punctuated by multiple loss-of-heterozygosity regions, whereas aneuploidies as well as segmental duplications are uncommon. Interestingly, triploid genomes are more prone to gene copy number variation than diploids. Finally, the pangenome of the species was reconstructed and was found to be small with few accessory genes compared with S. cerevisiae. The pangenome is composed of 5,409 ORFs (open reading frames) among which 5,106 core ORFs and 303 ORFs that are variable within the population. All these results highlight the different trajectories of species evolution and consequently the interest of establishing population genomic surveys in more populations.