Sucrose-promoted accumulation of growing glucosyltransferase variants of Streptococcus gordonii on hydroxyapatite surfaces

Abstract

Streptococcus gordonui exhibits a phase variation involving expression of high (Spp+) or low (Spp-) glucosyltransferase activity. The related bacterial accumulation on hydroxyapatite (HA) and saliva-coated HA surfaces was examined and found to be significant. Spp+ cells growing anaerobically in a defined medium utilize about 30% of the glucose available from sucrose to make insoluble glucans. These glucans formed cohesive masses on HA beads, which contained 80 to 90% of the total bacteria. The bacterial polymer mass had a volume of about 40 ,um3 and contained more than 5 x 10'°viable cells per cm3. In the absence of sucrose, the beads were saturated by 1 x 108 to 2 x 108 Spp+ cells. Spp-bacteria, which make 30-fold less glucan than do Spp+ bacteria, did not accumulate on surfaces in numbers significantly above the saturation level of 1 x 108 to 2 x 108 cells in the presence or absence of sucrose. Insoluble glucan synthesized by Spp+ cells from sucrose also enabled these bacteria to accumulate on saliva-coated HA seven times more effectively than the Spp-cells and 10 times more effectively than the Spp+ cells grown in medium without sucrose.

De novo glucan synthesis by mutans streptococcal glucosyltransferases present in pellicle promotes firm binding of Streptococcus gordonii to tooth surfaces

“…Actually, the 3H-labelled Challis and Is57 cells used in this study possessed a cell-associated GTF-activity of 2.5 and 0.0 mU per 10 s cells, respectively. Vickerman et al [29] have recently indicated that the strain Challis grown in a sucrose-supplemented FMC medium accumulates on glass surfaces, but its spontaneous GTF-negatire variant does not. Therefore, it is probable that the ceil-associated GTF activity of S. gordonii, in addition to mutans streptococcal GTF(s), participates in the sucrose-dependent celi-to-pellicle attachment of S. gordonii cells, However, whether the cell-associated activity is essential or not, and how many distinct GTFs are involved in this process, is yet unclear.…”

Sucrose‐dependent accumulation of oral streptococci and their adhesion‐defective mutants on saliva‐coated hydroxyapatite

“…Bacteria may bind directly to the enzyme and its glucan products (8,14,33) or may bind to amphipathic molecules such as lipoteichoic acids that are complexed to glucans (29,42). Although sucrose-associated accumulation mechanisms are best defined for mutans streptococci (24), recent evidence suggests that sucrose and resulting glucan synthesis may be important in the accumulation of 5. gordonii strain Challis (40). These in vitro studies show that accumulation may be facilitated by passive occlusion of multiplying bacterial cells, as glucans are synthesized in the developing dental plaque (41).…”

“…Cultures were mutagenized with nitrosoguanidine (28), cultured overnight in brain heart infusion broth (Difco Laboratories, Detroit, MI) and then washed and suspended in buffered KCl (1) to a concentration of IX10^ bacteria/ml. Bacterial suspensions were then mixed (Labquake, Labindustries, Berkeley, CA) with equal volumes of 2.5% (wt/vol) hydroxyapatite fiakes (BDH, Poole, UK) that had been coated with heat-sterilized (60°C), whole, unstimulated saliva (40). After 60 min of mixing, the fiakes were allowed to settle out by gravity, and the bacteria that remained unattached in the supernatants were cultured and subjected to additional rounds of selection with saliva-coated hydroxyapatite fiakes.…”

“…Adhesion tests with washed, nongrowing, ^H-thymidine (Amersham, about 50 Ci/mM)-labeled cells from mid-to late-log phase anaerobic cultures have been previously described (39,40). Briefly, bacterial suspensions in 1 ml of buffered KCl were mixed with 10 mg of hydroxyapatite or saliva-coated hydroxyapatite beads in polystyrene tubes on a rotating drum (New Brunswick Scientific Co., Edison, NJ) for 90 min at room temperature.…”

Molecular analysis of representative Streptococcus gordonii Spp phase variants reveals no differences in the glucosyltransferase structural gene, gtfG

“…Phase variation is thought to provide bacteria with ecologically advantageous alternatives (20), which could be particularly important in the rapid, extreme changes of the oral environment. Although the in vivo role of glucosyltransferase phase variation is unknown, in vitro studies with S. gordonii Spp"" and Spp" strains suggest that these cells have different abilities to attach to and accumulate on various surfaces under different environmental conditions (30)(31)(32) and provide intriguing preliminary evidence that glucosyltransferase phase variation may allow differential colonization of oral sites. Additional phenotypic changes in cell surface properties that potentially could affect colonization, such as the ability of the cells to coaggregate or produce hemolysin, also undergo reversible phase variation in S. gordonii (11).…”