Plasma-membrane alkali-metal-cation transporters involved in salt tolerance of pathogenic Candida species

Abstract

of Ph.D. Thesis Conclusions All the aims of the thesis were achieved. The tolerance to alkali metal cations of four pathogenic Candida species was studied in detail and revealed differences among the yeasts. These differences in sall tolerance remained the same under various growth conditions. For the first time, the internal sodium and potassium concentrations of several Candida species were estimated under high salt-stress grolvth. The internal K./Na* ratio was not in relation with the salt tolerance revealing different adaptation mechanisms to salt stress in Candida species. A first study on combinatory use of fluconazole and NaCl revealed severe synergistic effects of both compounds, leading to grovvth inhibition and increased internal Na* concentrationsi n C. albicans.T he molecularb asis of this synergismr emains to be established. Ihe C. dubliniensis, C. glabrata and C. parapsilosis Cnhl NalH- antiporters were cloned and functionally characterized upon heterologous expression in S. cerevlslae to understand the mechanisms involved in the different salttolerances of Candida species. The three antiporters differed in their activity for alkali metal cations, which roughly correlated with the observed differences in salt tolerance among the species. Additionally, during the characterization of...

of Ph.D.Thesis Conclusions All the aims of the thesis were achieved.The toleranceto alkali metalcationsof four pathogenic Candida species was studied in detail and revealed differencesamong the yeasts. These differences in sall tolerance remained the same under various growth conditions.For the first time, the internalsodium and potassiumconcentrationsof several Candidaspecieswere estimatedunder highsalt-stressgrolvth.The internalK./Na* ratiowas not in relationwith the salt tolerancerevealingdifferentadaptationmechanismsto salt stress in Candida species. A first study on combinatoryuse of fluconazoleand NaCl revealed severe synergisticeffects of both compounds, leading to grovvthinhibitionand increased internalNa* concentrationsin C. albicans.The molecularbasis of this synergismremainsto be established. Ihe C. dubliniensis, C. glabrata and C. parapsilosis Cnhl NalH- antiporters were cloned and functionallycharacterizedupon heterologousexpression in S. cerevlslae to understandthe mechanismsinvolvedin the differentsalttolerancesof Candidaspecies.The three antiportersdifferedin theiractivityfor alkalimetalcations,which roughlycorrelatedwith the observed differences in salt tolerance among the species. Additionally,during the characterizationof heteroiogouslyexpressed antiporters,two antiporter chimeras...