We have shown in previous studies that the glucosyltransferase (Gtf) enzymes of Streptococcus mutans have distinct properties when adsorbed to a surface. In the present study, we compared the activity of Gtf from Streptococcus sanguis, designated GtfSs, in solution and on the surface of saliva–coated hydroxyapatite (sHA) beads, and determined the ability of its product glucan to support the adherence of oral microorganisms. Gtf from S. sanguis 804 NCTC 10904 was purified from culture supernatant fluids by means of hydroxyapatite chromatography. Enzyme and the substrate were prepared in buffers at pH values from 3.5 to 7.5. Maximum activity of GtfSs occurred between pH 5.5 and pH 6.5, whether in solution or adsorbed onto a surface. The solubilized and insolubilized enzymes showed highest activity at 40°C; activity was reduced by 50(±2)% at 20 and 30°C. The enzyme did not form glucans in either phase at 10 or 60°C. The K_m, determined from Lineweaver–Burk plots, for the enzyme in solution was 4.3(±0.4) mmol/l sucrose, and the K_m for the enzyme on sHA beads was 5.0(±1.0) mmol/l sucrose. The ability of the GtfSs glucan synthesized on the surface of sHA beads to support the adherence of oral bacteria was investigated. ³H–thymidine–labeled bacteria (S. mutans GS–5, S. sobrinus 6715, S. sobrinus 6716, S. sanguis 10904, Actinomyces viscosus OMZ105E, A. viscosus 2085, and A. viscosus 2086) were incubated with sHA beads coated with GtfSs glucan. S. mutans GS–5 displayed the highest level of binding numerically. These results show that the GtfSs of S. sanguis is active on sHA beads, that the pH optimum for activity on a surface differs slightly from that in solution, and that its product glucan can support the adherence of oral microorganisms.

Glucosyltransferase (GTF) plays an essential role in the formation of the biofilm known as dental plaque and in the pathogenesis of dental caries. Mutans streptococci produce at least three distinct GTFs (GtfB, C and D), each of which forms a glucan polymer from sucrose. Glucan is a major constituent of plaque biofilm. GTF adsorbed to a surface forms glucans that differ in structure from those formed by the same enzyme in solution. In the present study, activities of GtfB and GtfC in solution or adsorbed on a surface were inhibited in the presence of a polyclonal antiserum (DS-1) to a mixture of GTFs and by immunoglobulin G (IgG) prepared from DS-1; in contrast, enzyme activity was enhanced by normal rabbit serum (NRS) and IgG from NRS. GtfD activity on a surface was enhanced by both antiserum DS-1 and NRS, and IgG prepared from either serum; GtfD activity in solution was slightly inhibited by each of the sera. The structure of GtfB and GtfC glucans formed in the presence of antiserum differed from that of controls based on linkage analyses, and on their susceptibilities to the glucanohydrolases mutanase (α-1,3 hydrolase) and dextranase (α-1,6 hydrolase); soluble products from the enzymatic digestion also differed. The results show that the effects of antibody on enzyme activity are more complex than simple inhibition or enhancement and that the presence of antibody may influence glucan structure, which clearly could impact plaque formation. The results have implications for the formation and properties of biofilms formed in other environments.

The aim of our study was to determine whether the structure of glucans formed by glucosyltransferase from Streptococcus sanguinis (GtfSs) on a surface differ from those formed in solution and to explore the effects of antiserum to Gtfs, control normal rabbit serum, starch hydrolysates (STH) and dextran on S. sanguinis (GtfSs) glucan. Linkage analyses showed that solution–formed glucans are predominantly α–1,6–linked and have a small amount of α–1,3–linked glucose. Surface–formed glucans have enhanced susceptibility to mutanase. Solution– and surface–formed glucans made in the presence or absence of sera, STH, and dextran contain linkages which differ in both amount and type from control glucans. The GtfSs enzyme in solution exposed to antiserum behaves as if it is adsorbed to a surface. Binding of Streptococcus mutans GS–5 and Actinomyces viscosus OMZ105E (Ny1) to S. sanguinis glucan differs if the glucan is formed in the presence of antiserum. The information could help to define the role of glucans in the formation of pellicle, colonization of tooth surfaces and the accumulation of dental plaque.