Sorbitol inhibition of glucose metabolism by Streptococcus sanguis 160

Abstract

Clinical studies in Sweden have shown that the proportion of sorbitol-utilizing strains of Streptococcus sanguis increases in dental plaque from individuals using sorbitol-containing products for prolonged periods. We have undertaken to study the metabolism of glucose and sorbitol by S. sanguis 160, isolated from a subject consuming sorbitol-containing chewing-gum 4 times a day for 4 years. Growth on glucose was inhibited by the presence of sorbitol in the growth medium and sorbitol was utilized in the presence of glucose, albeit, at a slower rate than glucose. In addition, pulses of glucose added to cultures growing on sorbitol resulted in the expulsion of sorbitol from the cell. In order to examine further the relationship of sorbitol and glucose, uptake assays were carried out with S. sanguis 160 grown in continuous culture (pH 7.0, dilution rate = 0.1 h-1) with glucose, sorbitol or nitrogen (sorbitol excess) limitations. The uptake of [14C]-glucose by sorbitol-limited cells, but not by glucose-limited cells, was inhibited by sorbitol, as was glycolysis. Kinetic experiments with glucose-limited cells showed 2 transport systems for glucose with Ks values of 5.2 and 40 microM, and glucose phosphorylation activity by decryptified cells indicated transport by the P-enolpyruvate (PEP) phosphotransferase system (PTS) with lesser activity for an ATP-dependent transport process. Transition from glucose-limited growth to sorbitol-limited growth revealed repression of total [14C]-glucose uptake by intact cells and activity for Enzyme II for glucose (Ellglc) of the PTS measured in membrane preparations in the presence of an excess of the soluble PTS proteins in crude cell-free supernatant fractions.(ABSTRACT TRUNCATED AT 250 WORDS)

Glucose transport by a mutant of Streptococcus mutans unable to accumulate sugars via the phosphoenolpyruvate phosphotransferase system

“…Sugar fermentation was determined by anaerobic incubation of the test organism on streptococcal sugar agar plates (2.0% Proteose Peptone, 0.5% yeast extract 0.5% NaCl, 0.1% Na 2 HPO 4 , 1.5% agar, 0.002% bromocresol purple) containing the various sugars at a concentration of 1%. The rate of acid production was measured by autotitration of metabolizing cells with standardized KOH as described previously (19).…”

“…The dried filters were then counted in 5.0 ml of Aquasol (NEN Research Products, Montreal, Quebec, Canada) in a liquid scintillation counter. Kinetics of glucose transport were determined essentially as previously described (19) with the concentrations of glucose ranging from 0.01 to 10 mM and the reactions being terminated at 0.1 min. Rates were expressed as nanomoles of sugar transported milligram (dry weight) of cell material Ϫ1 minute Ϫ1 .…”

The time‐course of acid excretion, levels of fluorescence dependent on cellular nicotinamide adenine nucleotide and glycolytic intermediates of Streptococcus mutans cells exposed and not exposed to air in the presence of glucose and sorbitol

“…It has been reported that the sugar alcohol is metabolized slowly by oral microorganisms ( 4, 7, 8) and inhibits glycolysis and growth of streptococci on glucose medium. Growth on glucose of Streptococcus sanguis 160 is inhibited by the presence of sorbitol in the growth medium and sorbitol is an effective catabolite repressor of the glucose‐phosphoenolpyruvate phosphotransferase system (glucose‐PEP PTS) ( 10). On the other hand, it has been shown that anaerobic sorbitol metabolism of oral streptococci is inhibited by exposure of the cells to air ( 1, 15, 19).…”

Identification of the Operon for the Sorbitol (Glucitol) Phosphoenolpyruvate:Sugar Phosphotransferase System in Streptococcus mutans

“…Sorbitol-PTS and SDH activities were repressed by low concentrations of glucose (8,19) by a mechanism that was at least in part due to inducer exclusion, a mechanism not observed with glucose-PTS-negative mutants. Sorbitol transport by Streptococcus sanguis also occurs via an inducible sorbitol-PTS (10,21); however, unlike S. mutans, S. sanguis is not subject to catabolite repression by glucose, being capable of growth on glucose and sorbitol concurrently, with sorbitol utilized at a slightly lower rate than glucose. The first sorbitol-PTS to be genetically characterized was from Escherichia coli L163sr (30,31).…”

“…Furthermore, a mutant defective in the general PTS protein, enzyme I, failed to ferment sorbitol (6), and sorbitol is not a substrate of the multiple-sugar metabolism transport system first reported by Tao and coworkers (24). As sorbitol metabolism in S. sanguis appears not to be subject to catabolite repression (10,21), it will be interesting to characterize the genetics of the sorbitol-PTS in this related oral bacterium.…”