B-167. A Eukaryotic-Type Serine/Threonine Protein Kinase and its Cognate Phosphatase are Required for Virulence in Streptococcus mutans

H. A. Hussain1, J. R. van der Ploeg2, E. Allan1;
1Univ. College London, London, UNITED KINGDOM, 2Univ. of Zurich, Zurich, SWITZERLAND.

Streptococcus mutans is the principal aetiological agent of dental caries in humans. Phenotypes associated with virulence include the ability to grow as a biofilm in dental plaque and the ability to tolerate low pH. The development of natural genetic competence may also aid survival in the oral cavity as it promotes genome plasticity and presumably, therefore, adaptation to changing environments. We have previously reported the presence of a putative membrane-located serine threonine protein kinase (encoded by pknB) and its cognate phosphatase (pppL) in S. mutans and shown that mutation of pknB causes defects in the development of genetic competence, in the ability to form biofilms and in the ability to grow at pH 5.0 (Hussain et al., 2006. J. Bacteriol. 188:1628). In this work we show that a pppL mutant and a pknB pppL double mutant also show defects in genetic competence and acid tolerance and the double mutant is defective in biofilm formation. As these phenotypes are thought to be important for virulence, we tested the ability of the mutants to colonise and cause disease in a rat model and found that they have reduced cariogenic capacity.