PgmNr Y3180: Identifying novel factors underlying stress resistance in the pathogenic yeast Candida glabrata.

Authors:
L. C. Ames 1 ; A. Cook 1 ; G. Cromie 2 ; E. Jeffery 2 ; A. Dudley 2 ; K. Haynes 1


Institutes
1) University of Exeter, Exeter, Devon, GB; 2) Pacific Northwest Diabetes Research Institute, Seattle, W.A., USA.


Keyword: Other Yeasts

Abstract:

The ability of pathogens, such as Candida species, to adapt to stresses encountered in the host environment is vital for survival and the establishment of infection. In particular, they must mount a robust response to reactive oxygen species in the phagosome. Despite highly homologous stress response pathways, C. glabrata is intrinsically more stress resistant than its close relative, the non-pathogenic yeast Saccharomyces cerevisiae. To identify novel factors contributing to such stress resistance in C. glabrata, mutants were generated for characterisation using two methods. Firstly, 96 C. glabrata mutants resistant to tBOOH, an oxidative stress-inducing chemical, were produced by EMS mutagenesis. Secondly, in vitro passaging experiments were used to force evolution of tBOOH- and H2O2-resistant phenotypes in C. glabrata.

Characterisation of EMS mutants revealed that the acquisition tBOOH resistance was accompanied by a fitness trade-off where mutants either became less fit under non-stress conditions or became more susceptible to another type of stress. Most notably, 70 % of tBOOH-resistant EMS mutants became more susceptible to the antifungal drug fluconazole. Surprisingly, C. glabrata strains passaged in H2O2 showed no fitness defect under stress-free conditions. The virulence of stress-resistant mutants is currently being investigated in a newly-optimised Galleria mellonella model of C. glabrata infection.

Whole genome sequencing was performed on all stress-resistant EMS and passaged mutants, revealing over 4000 polymorphism calls and 14 aneuploidy events. Recreation of selected polymorphisms into the parental strain background, by site directed mutagenesis, will identify mutations contributing to stress resistance in C. glabrata.