The uptake of fructose by Pseudomonas putida

Fructose transport was not apparently affected in a number of Pseudomonas putida strains with deranged activity of a common glucose-gluconate uptake system, indicating the existence of an independent fructose uptake system. Fructose uptake by glucose-gluconate uptake mutants was induced by fructose and obeyed saturation kinetics (apparent K _m =0.3 mM). The fructose uptake system serves to transport glucose in addition to fructose. The entry of fructose into P. putida cells appears to be mediated also by the glucose-gluconate uptake system, as shown by the ability to accumulate fructose of wild type cells grown on glucose, a substrate that induces the glucose-gluconate uptake system but not the fructose uptake system. In addition, fructose was found to be an inducer of the glucose-gluconate uptake system. The physiological significance of these observations is not clear because the fructose uptake system can provide the cell with a high enough internal concentration of fructose to support maximum growth rate on this hexose, as shown by following the growth course of glucose-gluconate uptake mutants on fructose.