Taxonomy and genomics of Kazachstania yeasts from sourdough

Introduction: Yeast diversity has now been well investigated in natural sourdoughs isolated from Asian and European countries. However, the yeast diversity of natural sourdoughs made of organic wheat has never been studied. Microbial and molecular approaches to study this type of sourdoughs from France revealed that Saccharomyces cerevisiae was not the dominant species, questioning its implication as natural baker yeast and most dominant yeast species belong to the Kazachstania clade (Lhomme et al, 2016). Results and Discussion: Using ribosomal RNA gene and protein coding gene sequences, a thorough taxonomic analysis of sourdough strains isolated from France, identified two novel species in a subclade of the Kazachstania clade known to harbor a number of baker’s yeasts, such as Candida humilis and Candida milleri. In addition, two other novel species were identified in this subclade, one from rotting wood in Brazil and one from soil in South Africa, the latter consisting of a strain previously wrongly assigned to the Kazachstania exigua species. Further analysis revealed that the K. exigua species was very heterogeneous and made of haploid, alloploid and hybrid isolates, as suggested by Bon et al. (2000). Comparison of the genome of strains from sourdough and their corresponding type strains identified a number of specific genes, but did not show extensive differences at the genomic level, suggesting that strains isolated from sourdough differ mainly from non-sourdough strains at the transcriptional level. Finally, sequence analysis of major baker’s yeasts revealed several features, such as rearrangements at the mating type loci, distribution of Whole Genome Distribution gene blocks and distribution of transposons. These will be discussed.