Glucose Uptake Kinetics and Transcription of HXTGenes in Chemostat Cultures of Saccharomyces cerevisiae

Abstract

The kinetics of glucose transport and the transcription of all 20 members of the <i>HXT</i> hexose transporter gene family were studied in relation to the steady state<i>in situ</i> carbon metabolism of <i>Saccharomyces cerevisiae</i> CEN.PK113-7D grown in chemostat cultures. Cells were cultivated at a dilution rate of 0.10 h⁻¹ under various nutrient-limited conditions (anaerobically glucose- or nitrogen-limited or aerobically glucose-, galactose-, fructose-, ethanol-, or nitrogen-limited), or at dilution rates ranging between 0.05 and 0.38 h⁻¹ in aerobic glucose-limited cultures. Transcription of<i>HXT1–HXT7</i> was correlated with the extracellular glucose concentration in the cultures. Transcription of <i>GAL2</i>, encoding the galactose transporter, was only detected in galactose-limited cultures. <i>SNF3</i> and <i>RGT2</i>, two members of the <i>HXT</i> family that encode glucose sensors, were transcribed at low levels. <i>HXT8–HXT17</i> transcripts were detected at very low levels. A consistent relationship was observed between the expression of individual <i>HXT</i> genes and the glucose transport kinetics determined from zero-<i>trans</i>influx of ¹⁴C-glucose during 5 s. This relationship was in broad agreement with the transport kinetics of Hxt1–Hxt7 and Gal2 deduced in previous studies on single-<i>HXT</i> strains. At lower dilution rates the glucose transport capacity estimated from zero-<i>trans</i> influx experiments and the residual glucose concentration exceeded the measured <i>in situ</i> glucose consumption rate. At high dilution rates, however, the estimated glucose transport capacity was too low to account for the <i>in situ</i> glucose consumption rate.