Genome dynamics and virulence in the human pathogen Candida glabrata

Abstract: Popular Abstract in English Candida glabrata is currently the second most usual cause of yeast infections. This yeast is phylogenetically more related to Saccharomyces cerevisiae than to Candida albicans. Many systemic infections have recently been found associated with C. glabrata yeast. Apparently, this yeast can easily reshuffle its genome and this is one of the topics of my thesis. During the last decades a few studies have been conducted to find out the mechanisms behind the pathogenicity of C. glabrata. Some of these studies have found that C. glabrata can adapt to the harsh conditions by changing the number and the size of chromosomes also intra- and inter-chromosomal segmental duplications have been observed. One part of my study was to focus on the mechanisms involved in the genome rearrangements that are likely a way how to survive in the human and to become resistant to azole antifungal therapy. C. glabrata is an asexual yeast and only haploid isolates have been found so far. Organisms can adapt to a new environment by rearranging their chromosomes. The ploidy and genomic instability have been reported to be associated with increased virulence. In my thesis we generated hybrids of C. glabrata isolates and we let them grow under different stressful conditions including high temperature and the presence of azole. The aim of this experiment was to find out which strain, haploid or diploid, was more resistant to harsh environments. The competition was conducted in vitro and in vivo using the fly and mouse models. The genes that were highly expressed to overcome the stress were elucidated by microarrays. Like other budding yeasts, C. glabrata has lost RNA interference pathway which is involved in the regulation of gene expression. In human, this pathway has been reported to play a crucial role in silencing genes related to some diseases. The scientists were able to silence some genes in Saccharomyces cerevisiae by reconstitution of RNAi system from Saccharomyces castellii. The beauty of this tool is that one can study the function of essential genes which can otherwise not be deleted. RNAi tool was successfully designed in our laboratory and we could silence URA3 and ADE2 and putative virulence genes and could study the resulting strains in the macrophage cell cultures.