Understand the genomic diversity and evolution of fungal pathogen Candida glabrata by genome-wide analysis of genetic variations.

The yeast Candida glabrata, an opportunistic human fungal pathogen, is the second most prevalent cause of candidiasis worldwide, with an infection incidence that has been increasing in the past decades. The completion of the C. glabrata reference genome made fundamental contributions to the understanding of the molecular basis of its pathogenic phenotypes. However, knowledge of genome-wide genetic variations among C. glabrata strains is limited. In this study, we present a population genomic study of C. glabrata based on whole genome re-sequencing of 47 clinical strains to an average coverage of ∼63×. Abundant genetic variations were identified in these strains, including single nucleotide polymorphisms (SNPs), small insertion/deletions (indels) and copy number variations (CNVs). The observed patterns of variations revealed clear population structure of these strains. Using population genetic tests, we detected fast evolution of several genes involved in C. glabrata adherence ability, such as EPA9 and EPA10. We also located genome structural variations, including aneuploidies and large fragment CNVs, in regions that are functionally related to virulence. Subtelometric regions were hotspots of CNVs, which may contribute to variation in expression of adhesin genes that are important for virulence. We further conducted a genome-wide association study that identified two SNPs in the 5'UTR region of CST6 that were associated with fluconazole susceptibility. These observations provide convincing evidence for the highly dynamic nature of the C. glabrata genome with potential adaptive evolution to clinical environments, and offer valuable resources for investigating the mechanisms underlying drug resistance and virulence in this fungal pathogen. (249 words).

Genome structure and dynamics of the yeast pathogen Candida glabrata.

The yeast pathogen Candida glabrata is the second most frequent cause of Candida infections. However, from the phylogenetic point of view, C. glabrata is much closer to Saccharomyces cerevisiae than to Candida albicans. Apparently, this yeast has relatively recently changed its life style and become a successful opportunistic pathogen. Recently, several C. glabrata sister species, among them clinical and environmental isolates, have had their genomes characterized. Also, hundreds of C. glabrata clinical isolates have been characterized for their genomes. These isolates display enormous genomic plasticity. The number and size of chromosomes vary drastically, as well as intra- and interchromosomal segmental duplications occur frequently. The observed genome alterations could affect phenotypic properties and thus help to adapt to the highly variable and harsh habitats this yeast finds in different human patients and their tissues. Further genome sequencing of pathogenic isolates will provide a valuable tool to understand the mechanisms behind genome dynamics and help to elucidate the genes contributing to the virulence potential.