High-affinity iron and calcium transport pathways are involved in U(VI) uptake in the budding yeast Saccharomyces cerevisiae
Uranium (U) is a naturally-occurring radionuclide toxic for living organisms that can take it up. To date, the mechanisms of U uptake are far from being understood. Here, we used the yeast Saccharomyces cerevisiae as a unicellular eukaryote model to identify U assimilation pathways. Thus, we have identified, for the first time, transport machineries capable of transporting U in a living organism. First, we evidenced a metabolism-dependent U transport in yeast. Then, competition experiments with essential metals allowed us to identify calcium, iron and copper entry pathways as potential routes for U uptake. The analysis of various metal transport mutants revealed that mid1{Delta}, cch1{Delta} and ftr1{Delta} mutants, affected in calcium (Mid1/Cch1 channel) and Fe(III) (Ftr1/Fet3 complex) transport, respectively, exhibited highly reduced U uptake rates and accumulation, demonstrating the implication of these import systems in U uptake. Finally, expression of the Mid1 gene into the mid1{Delta} mutant restored U uptake levels of the wild type strain, underscoring the central role of the Mid1/Cch1 calcium channel in U absorption process in yeast. Our results also open up the opportunity for rapid screening of U-transporter candidates by functional expression in yeast, before their validation in more complex higher eukaryote model systems. HighlightsO_LILiving yeast Saccharomyces cerevisiae is able to take up U C_LIO_LIAvailability of a metabolizable substrate stimulates U uptake C_LIO_LICalcium, iron and copper inhibit U uptake C_LIO_LIStrains deleted in Mid1/Cch1 calcium channel and Ftr1 iron permease are affected in U uptake C_LIO_LIExpression of MID1 gene in mid1{Delta} strain restore wild type levels of U uptake C_LI O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=95 SRC="FIGDIR/small/447839v1_ufig1.gif" ALT="Figure 1"> View larger version (27K): org.highwire.dtl.DTLVardef@153dbe0org.highwire.dtl.DTLVardef@8874bcorg.highwire.dtl.DTLVardef@a7f353org.highwire.dtl.DTLVardef@57feb1_HPS_FORMAT_FIGEXP M_FIG Graphical Abstract C_FIG