Wild-type cells of Candida albicans, the most common human fungal pathogen, are able to grow at very low micromolar concentrations of potassium in the external milieu. One of the reasons behind that behaviour is the existence of three different types of K+ transporters in their plasma membrane: Trk1, Acu1 and Hak1. This work shows that the transporters are very differently regulated at the transcriptional level upon exposure to saline stress, pH alterations or K+ starvation. We propose that different transporters take the lead in the diverse environmental conditions, Trk1 being the "house-keeping" one, and Acu1/Hak1 dominating upon K+ limiting conditions. Heterologous expression of the genes coding for the three transporters in a Saccharomyces cerevisiae strain lacking its endogenous potassium transporters showed that all of them mediated cation transport but with very different efficiencies. Moreover, expression of the transporters in S. cerevisiae also affected other physiological characteristics such as sodium and lithium tolerance, membrane potential or intracellular pH, being, in general, CaTrk1 the most effective in keeping these parameters close to the usual wild-type physiological levels.

Department of Biochemistry and Molecular Biology Campus de Excelencia Internacional Agroalimentario CeiA3 University of Córdoba 14071 Córdoba Spain

Department of Microbiology University of Córdoba 14071 Córdoba Spain

Laboratory of Membrane Transport Institute of Physiology Czech Academy of Sciences 142 20 Prague 4 Czech Republic

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The superior growth of Kluyveromyces marxianus at very low potassium concentrations is enabled by the high-affinity potassium transporter Hak1

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Yeast Trk1 Potassium Transporter Gradually Changes Its Affinity in Response to Both External and Internal Signals