Effect of temperature on the uptake of glucose, gluconate, and 2-ketogluconate by Pseudomonas fluorescens

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Abstract
The effect of temperature on the uptake systems involved with glucose catabolism was studied in a psychrotrophic strain of Pseudomonas fluorescens. The Km values for glucose and gluconate uptake were approximately 1 and 30 μM respectively whether uptake was assayed at 30 or 5 °C. The Km for 2-ketogluconate (2-KG) uptake was approximately 40 μM assayed at 30 °C and 20 μM assayed at 5 °C. Little or no induction of 2-KG uptake was detected in cells grown at 30 °C with glucose or gluconate. High induced levels of 2-KG uptake were observed in cells grown at 5 °C. The induced level of glucose uptake in cells grown at 5 °C with glucose was only one-half the induced level in cells grown at 30 °C with glucose (when activities were compared at the same assay temperature). The effect of low-assay temperature on the activities of these uptake systems was most pronounced for gluconate. When the assay temperature was decreased from 30 to 5 °C, uptake activity decreased 12-fold, 6-fold, and 5-fold for gluconate, glucose, and 2-KG, respectively. Because of the differential effect of temperature on the induction of glucose uptake and on the activity of glucose, gluconate, and 2-KG uptake, the major uptake activity measured in cells grown at 5 °C with glucose or gluconate was through 2-KG. Glucose and 2-KG appeared to inhibit significantly gluconate uptake and (or) catabolism which might promote the continued oxidation of gluconate to 2-KG at low growth temperatures. The results confirm the lack of glucose or gluconate catabolism by the direct oxidative non-phosphorylated pathway through 2-KG at higher growth temperatures and the major function of this pathway at lower growth temperatures.