FUNCTIONAL EXPRESSION OF THE GLUCOSE-TRANSPORTER OF ZYMOMONAS-MOBILIS LEADS TO RESTORATION OF GLUCOSE AND FRUCTOSE UPTAKE IN ESCHERICHIA-COLI MUTANTS AND PROVIDES EVIDENCE FOR ITS FACILITATOR ACTION

The Zymomonas mobilis genes encoding the glucose facilitator (glf), glucokinase (glk), or fructokinase (frk) were cloned and expressed in a lacI(q)-Ptac system using Escherichia coli K-12 mutants deficient in uptake and phosphorylation of glucose and fructose. Growth on glucose or fructose was restored when the respective genes (glf-glk or glf-frk) were expressed. In E. coli glf(+) strains, both glucose and fructose were taken up via facilitated diffusion (K-m, 4.1 mM for glucose and 39 mM for fructose; V-max at 15 degrees C, 75 and 93 nmol min(-1) mg(-1) [dry weight] for glucose and fructose, respectively). For both substrates, counterflow maxima were observed.