| Summary: | <p>Abstract</p> <p>Background</p> <p>The gene family of hexose transporters in <it>Saccharomyces cerevisiae </it>consists of 20 members; 18 genes encoding transporters (<it>HXT1-HXT17</it>, <it>GAL2</it>) and two genes encoding sensors (<it>SNF3</it>, <it>RGT2</it>). The effect of oxygen provision on the expression of these genes was studied in glucose-limited chemostat cultivations (D = 0.10 h<sup>-1</sup>, pH 5, 30°C). Transcript levels were measured from cells grown in five steady state oxygen levels (0, 0.5, 1, 2.8 and 20.9% O<sub>2</sub>), and from cells under conditions in which oxygen was introduced to anaerobic cultures or removed from cultures receiving oxygen.</p> <p>Results</p> <p>The expression pattern of the <it>HXT </it>gene family was distinct in cells grown under aerobic, hypoxic and anaerobic conditions. The transcription of <it>HXT2</it>, <it>HXT4 </it>and <it>HXT5 </it>was low when the oxygen concentration in the cultures was low, both under steady state and non-steady state conditions, whereas the expression of <it>HXT6</it>, <it>HXT13 </it>and <it>HXT15/16 </it>was higher in hypoxic than in fully aerobic or anaerobic conditions. None of the <it>HXT </it>genes showed higher transcript levels in strictly anaerobic conditions. Expression of <it>HXT9</it>, <it>HXT14 </it>and <it>GAL2 </it>was not detected under the culture conditions studied.</p> <p>Conclusion</p> <p>When oxygen becomes limiting in a glucose-limited chemostat cultivation, the glucose uptake rate per cell increases. However, the expression of none of the hexose transporter encoding genes was increased in anaerobic conditions. It thus seems that the decrease in the moderately low affinity uptake and consequently the relative increase of high affinity uptake may itself allow the higher specific glucose consumption rate to occur in anaerobic compared to aerobic conditions.</p>
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