2Department of Biochemistry and Biophysics, Stockholm University, S-106 91 Stockholm, and Department of Chemistry and Biomedical Sciences, Kalmar University, S-391 82 Kalmar, Sweden
* To whom correspondence should be addressed.
Received July 9, 2004
A newly isolated osmo-, salt-, and alkalitolerant Yarrowia lipolytica yeast strain is distinguished from other yeast species by its capacity to grow vigorously at alkaline pH values (9.7), which makes it a promising model organism for studying Na+-dependent phosphate transport systems in yeasts. Phosphate uptake by Y. lipolytica cells grown at pH 9.7 was mediated by several kinetically discrete Na+-dependent systems specifically activated by Na+. One of these, a low-affinity transporter, operated at high concentrations of extracellular phosphate. The other two, high-affinity systems, maximally active in phosphate-starved cells, were repressed or derepressed depending on the prevailing extracellular phosphate concentration and pH value. The contribution of Na+/Pi-cotransport systems to the total cellular phosphate uptake progressively increased with increasing pH, reaching its maximum at pH >= 9.
KEY WORDS: Yarrowia lipolytica, yeast, cytoplasmic membrane, phosphate transport, Na+/Pi-cotransport system, regulation