Sorbitol transport by <em>Streptococcus sanguis</em> 160.

Sorbitol metabolism was examined with a sorbitol-fermenting strain (160) of Streptococcus sanguis isolated from the dental plaque of a subject using sorbitol-containing chewing-gum for 4 years. S. sanguis 160 was grown in continuous culture (pH, 7.0; dilution rate, 01 h-1) with glucose, sorbitol and nitrogen (sorbitol-excess) limitations. Cells grown with a glucose limitation exhibited low, but detectable, uptake of [14C]-sorbitol and transition to medium limiting in sorbitol resulted in a 5-fold increase in sorbitol uptake. Kinetic data revealed that both glucose and sorbitol-limited cells possessed 2 transport systems for sorbitol (Ks=3.3-6.7 and 36-64 μM), but continued growth of the organism on limiting sorbitol resulted in the loss of the high-affinity system. Decryptified, sorbitol-limited cells phosphorylated sorbitol in the presence of phosphoenolpyruvate (PEP), but not with ATP, indicating sorbitol transport solely via the PEP phosphotransferase (PTS) system. PEP-dependent activity in glucose-limited and sorbitol-excess cells was 6- and 4-fold lower than that of the sorbitol-limited cells. Uptake of [14C]-sorbitoI and activity for Ell for sorbitol [Ellsor of the PTS in cells in transition from a glucose to sorbitol-limitation confirmed the induction of the sorbitol-PTS and the repression of the glucose-PTS in the presence of sorbitol. Cells grown with an excess of sorbitol exhibited very low Ellsor activity. A crossover experiment with membranes and soluble fractions from glucose-,sorbitol- and nitrogen-limited cells of S. sanguis 160 demonstrated the induction of a soluble PTS component in sorbitol-limited cells essential for sorbitol transport via the PTS. In addition, this factor, tentatively identified as IIIsor, was shown to stimulate 7-fold sorbitol phosphorylation by glucose-limited membranes, indicating the possibility that sorbitol. [ABSTRACT FROM AUTHOR]