Catabolism of D-glucose by Pseudomonas putida U occurs via extracellular transformation into D-gluconic acid and induction of a specific gluconate transport system

Pseudomonas putida U does not degrade D-glucose through the glycolytic pathway but requires (i) its oxidation to D-gluconic acid by a peripherally located constitutive glucose dehydrogenase (insensitive to osmotic shock), (ii) accumulation of D-gluconic acid in the extracellular medium, and (iii) the induction of a specific energy-dependent transport system responsible for the uptake of D-gluconic acid. This uptake system showed maximal rates of transport at 30 degrees C in 50 mM potassium phosphate buffer, pH 7.0. Under these conditions the K-m calculated for D-gluconic acid was 6.7 mu M. Furthermore, a different transport system, specific for the uptake of glucose, was also identified. It is active and shows maximal uptake rates at 35 degrees C in 50 mM potassium phosphate buffer, ph 6.0, with a K-m value of 8.3 mu M.