The role of the Streptococcus mutans glucosyltransferases in the sucrose-dependent attachment to smooth surfaces: essential role of the GtfC enzyme.

Previous results have indicated that the glucosyltransferase activities of mutans streptococci are required for sucrose-dependent colonization of tooth surfaces. We have constructed mutants of Streptococcus mutans GS5 that are altered in varying combinations of the three gtf genes present in this organism. A quantitative in vitro sucrose-dependent attachment system was used to demonstrate that the inactivation of the gtfC gene drastically reduced adherence to smooth surfaces. By contrast, inactivation of the gtfB gene resulted in a smaller, but significant, reduction in attachment while the gtfD mutant was only marginally affected. Furthermore, production of only the glucosyltransferase C enzyme allowed for attachment although at reduced levels compared to the wild-type organism. The results from reintroduction of single copies of each of the gtf genes into a mutant of strain GS5 lacking glucosyltransferase activity also demonstrated the crucial role of the glucosyltransferase C enzyme in colonization. These results suggest a unique role for the glucosyltransferase C enzyme in the sucrose-dependent colonization of tooth surfaces by S. mutans strains.