[Initial-plaque forming ability of glucosyltransferases from Streptococcus mutans serotype C strain]

In order to clarify functional roles of extracellular glucosyltransferases (GTases) from S. mutans serotype c in initial stage of plaque formation, GTase-I and GTase-S were purified from culture fluids of strain PS 14. And an ability of these GTases to enhance cellular attachment of oral streptococci was investigated using 3H labeled resting cells of S. sanguis Challis and S. milleri Is 57. The results were as follows: 1) From culture fluids of strain PS 14 grown in a M 4 medium supplemented with 1% ammonium sulfate, GTase-I was purified by ammonium sulfate fractionation, CM-cellurose column chromatography and Toyopearl HW-55 gelfiltration. Also, GTase-S was purified by the method of Baba et al from the culture fluids of strain PS 14 grown in a dialyzed BHI medium. Purified GTase-I and GTase-S were almost homogeneous, and had a molecular size of 160 KDa and 145 KDa respectively (by SDS-PAGE). 2) Sucrose-dependent attachment of S. sanguis cells to experimental pellicles was markedly enhanced by the addition of crude GTase in saliva. This fact was conformed by a scanning electron microscopic observation of the attachment cells. Such enhanced attachment necessitated a long-term incubation (greater than 10 h) of the cells in the presence of sucrose, suggesting that it is correlated to de novo glucan synthesis. 3) Purified GTase-I also had an ability to enhance the cellular attachment of S. sanguis cells as well as crude GTase, while purified GTase-S didn't have. Neither crude enzyme, GTase-I nor GTase-S have an ability to enhance significantly the cellular attachment of S. milleri cells. However, S. milleri pretreated with the preparations containing GTase-S gained the ability to attach to experimental pellicles prepared from saliva supplemented with GTase-I. These results suggest that the cellular attachment system mediated by enzymatic action (s) of GTase (s) from serotype c S. mutans be present and function in the first stage of plaque formation.