A novel alkali-tolerant Yarrowia lipolytica strain for dissecting Na+-coupled phosphate transport systems in yeasts

The newly isolated osmo-, salt- and alkali-tolerant Yarrowia lipolytica yeast strain is remarkable by its capacity to grow at alkaline pH values (pH 9.7), which makes it an excellent model system for studying Na+-coupled phosphate transport systems in yeast cells grown at alkaline conditions. In cells Y. lipolytica grown at pH 9.7, phosphate uptake was mediated by several kinetically discrete Na+-dependent systems that are specifically activated by Na+ ions. One of these, a low-affinity transporter, operated at high-phosphate concentrations. The other two, derepressible, high-affinity, high-capacity systems, functioned during phosphate starvation. Both H+- and Na+-coupled high-affinity phosphate transport systems of Y. lipolytica cells were under the dual control of the prevailing extracellular phosphate concentrations and pH values. The contribution of the Na+/Pi-cotransport systems into the total cellular phosphate uptake activity was progressively increased with increasing pH, reaching its maximum at pH ≥ 9.