Xylitol-mediated transient inhibition of ribitol utilization by Lactobacillus casei

The growth of Lactobacillus casei strain Cl-16 at the expense or ribitol was inhibited if the non-metabolizable substrate xylitol was included in the medium at concentrations of 6 mM or greater. At these concentrations, xylitol, did not competitively inhibit ribitol transport. The cessation of growth was caused by the intracellular accumulation of xylitol-5-phosphate, which occurred because growth on ribitol had gratuitously induced a functional xylitol-specific phosphotransferase system but not the enzymes necessary for the further metabolism of xylitol-5-phosphate. Eventually, the cells overcame the xylitol-mediated inhibition by repressing the synthesis of enzyme II of the xylitol phosphotransferase system so that xylitol-5-phosphate would no longer be accumulated within the cell.