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Alakali-metal-cation homeostasis in pathogenic Candida species
Elicharová, Hana ; Sychrová, Hana (advisor) ; Heidingsfeld, Olga (referee) ; Půta, František (referee)
Several tens of Candida species belong to the opportunistic human pathogens capable of inducing life-threatening infections in immunocompromised patients. Virulence of single Candida species depends among others on their resistance to the variable external conditions. The maintenance of alkali-metal-cation homeostasis, which means the ability to accumulate sufficient amount of potassium cations and on the other hand to survive under high extracellular concentrations of alkali-metal cations, is essential for growth and virulence of Candida cells. We observed the negative effect of fluconazole (FLC) on salt-tolerance of six Candida species and found that it is independent of the species level of FLC- resistance. FLC hyperpolarizes plasma membrane of Candida cells and therefore increases non-specific uptake of alkali-metal cations which results in strongly increased salt-sensitivity of Candida cells. The FLC-induced hyperpolarization also results in an increased sensitivity of Candida cells to the antifungals which are positively charged and are driven into the cells by the membrane potential. The effect of fluconazole on membrane potential and thus on the uptake of alkali- metal cations into the cell turned our attention to the homeostasis of potassium cations whose high intracellular concentration is...
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The role of transport systems for potassium cations in the physiology of Saccharomyces cerevisiae yeast
Marešová, Lydie ; Sychrová, Hana (advisor) ; Pácha, Jiří (referee) ; Janderová, Blanka (referee)
[n this work, we present the characteristics of kha 1 6,. strains in the background of various multiple mutations in genes encoding alkali-metal-cation transporters. Two main phenotype manifestations of the khal deletion were growth defect on high externa\ pH and hygromycin sensitivity. The correlation between these phenotypes and the kha 1 deletion was confirmed by plasmid complementation. Fluorescence microscopy of GFP-tagged Kha 1 p showed that this antiporter is localized preferentially intracellu\arly (in contrast to the plasma-membrane Na+/H+ antiporter Nha 1 p). Based on these findings, Kha 1 p is probably not localized in plasma membrane and do es not mediate efflux of alkali metal cations from cells (as published before in RammÍrez el aJ., 1998), but is important for the regulation of intracelular cation homeostasis and optima\ pH contro l, similarly as the Nhx l p. The khal deletion phenotypes were complemented by heterologous expression of a plant antiporter AtChx 17, showing that the proteins AfChx 17 and SeKhal could have similar ťunction and that S cerevisiae khal deletion mutants could serve for heterologous expression and characterization of some plant transporters in yeast, especially those localized intracellularly. We also showed that the presence of the Tokl channel strongly infl uences...
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