Characterization of Phosphate Membrane Transport in Saccharomyces cerevisiae CEN.PK113-5D under Low-Phosphate Conditions Using Aerobic Continuous Culture

Abstract

<em>Two different growth media, namely complex and defined media, were used to examine establishment of steady-state conditions in phosphate-limited culture system of Saccharomyces cerevisiae CEN.PK113-5D strain. Using the defined growth medium, it was possible to obtain steady state condition in the continuous culture. The effect of phosphate concentration on the growth of S. cerevisiae in phosphate-limited chemostat was studied at dilution rates between 0.08-0.45 h^–1. The cells' growth followed Monod kinetics only over low dilution rates (0.08-0.22 h^–1) in which the saturation constant (K_S) and maximum growth rate (μ_m) were determined as 10 µM and 0.25 h^–1, respectively. By increasing the dilution rates above 0.22 h^–1, a significant change in the growth pattern was occurred, possibly due to intracellular accumulation of phosphate and/or extracellular accumulation of ethanol and also increased fermentative activity of the yeast cells. </em> <em>Phosphate transport of the yeast cells via plasma membrane transporters was kinetically characterized in a phosphate-limited chemostat culture. The rate of phosphate transport was measured using³²[P]-labeled orthophosphate in the concentration range of 0.4-2000 µM. High-affinity phosphate transport kinetics was observed over the entire range of dilution rates tested in this study. The corresponding K_m values for phosphate were found to be in the range of 1.7 to 36 µM. Dilution rate of 0.22 h^–1 showed biphasic pattern for phosphate uptake kinetics while the estimated K_m values for this behavior were 1.7 and 284 µM.</em>