Xylose transport insensitivity to catabolite inhibition by phosphoenolpyruvate:Sugar phosphotransferase system in tetragenococcus halophila

Tetragenococcus halophila accumulates glucose and 2-deoxyglucose (dGlc) via the phosphoenolpyruvate:sugar phosphotransferase system (PTS), and pentoses, maltose, and glycerol via non-PTS carriers. Based on the discovery that xylose metabolism in T. halophila was subject to catabolite repression but not to catabolite inhibition, we designed a selection protocol for thermosensitive mutants pleiotropically unable to use sugars. One such mutant was a ptsI mutant with a thermosensitive enzyme I (EI) of the PTS (leaky at 30°C). Using this ptsI mutant, catabolite inhibition was studied. dGlc was more strongly inhibitory of glycerol uptake in the mutant than in the parent because of the leaky ptsI mutation. Thermoinactivation of EI at 42°C resulted in the total loss of uptake of PTS sugars and in the virtual abolishment of glycerol uptake. However, xylose uptake of the ptsI mutant was scarcely inhibited by dGlc even after thermoinactivation of EI. These results suggest that sensitivities of non-PTS uptakes to PTS-mediated inhibition vary among non-PTS su.