FUNCTIONAL EXPRESSION OF THE GLUCOSE-TRANSPORTER OF ZYMOMONAS-MOBILISLEADS 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), gl ucokinase (glk), or fructokinase (frk) were cloned and expressed in a lacI(q)-Ptac system using Escherichia coli K-12 mutants deficient in u ptake and phosphorylation of glucose and fructose. Growth on glucose o r 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 3 9 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 subst rates, counterflow maxima were observed.