Streptococcus mutants, the principal etiologic agent of dental caries in humans, infects more than 95% of the population worldwide often colonizing the oral cavity during the first year of life. Among the attributes which contribute to S. mutans-induced caries formation is the metabolism of dietary carbohydrates; this results in the production of copious quantities of lactic acid in the oral cavity. The production of acid and the concomitant decrease in pH leads to the demineralization of tooth enamel and the onset of dental decay. In addition to the production of acid from dietary carbohydrates is the ability of S. mutans to metabolize intracellular polysaccharides (IPS), glycogen-like storage polymers containing alpha-1,4 and alpha-1,6 glucosyl linkages. IPS may therefore contribute to the cariogenic potential of S. mutans by prolonging the period of exposure of host tissues to organic acids, especially when exogenous carbohydrates are lacking from the oral cavity such as at non-meal times. We have recently demonstrated that S. mutans IPS are indeed significant contributors to the caries-forming process; that is, an IPS-deficient mutant which bears a deletion at a locus (glg) putatively involved in S. mutans IPS accumulation is significantly less cariogenic then its wild-type progenitor in a germfree rat model (p<0.01). Moreover, we recently reported a S. mutans transposon mutant which accumulates IPS in excess of wild-type levels to be significantly hypercariogenic in germfree rats (p<0.01). The main objective of the present proposal is to elucidate the structural organization of the cloned glg locus from S. mutans and to investigate the mechanism by which S. mutans IPS accumulation is potentially regulated during cariogenesis. These studies will further our understanding of the events which lead to acid production in the plaque environment.
Specific aims i nclude: 1. the continued nucleotide sequence analysis of the S. mutans glg locus and analysis of glg gene products; 2. the construction of glg operon fusion strains so that transcriptional activity may be monitored in vitro. Glycogen gene expression will be assessed in a variety of environments likely to be encountered by the organism in the oral cavity.
