Analyses of glucans from cariogenic and mutant Streptococcus mutans

Area of Science:

• Microbiology
• Biochemistry
• Oral Health Research

Background:

• Cariogenic Streptococcus mutans synthesizes extracellular and cell-associated glucans.
• Glucan structure influences bacterial virulence and biofilm formation.
• Understanding glucan composition is key to developing anti-caries strategies.

Purpose of the Study:

• To quantitatively and qualitatively analyze glucans from wild-type (WT) Streptococcus mutans and its virulence-defective mutants.
• To elucidate the structural differences and linkage types in glucans synthesized by WT and mutant strains.
• To correlate glucan structure with bacterial virulence.

Main Methods:

• Methylation analysis to determine glucan linkage composition.
• Gel chromatography to assess glucan molecular weight and polydispersity.
• Enzymatic hydrolysis using dextranase and alpha-(1 --> 3)-hydrolyzing enzymes.

Main Results:

• Mutants synthesized more alpha-(1 --> 6)-rich extracellular glucans than WT, with some cell association.
• WT produced a distinct, highly branched, alpha-(1 --> 3)-rich cell-associated polymer.
• Both glucan types contained mixtures of alpha-(1 --> 3) and alpha-(1 --> 6) linkages and were sensitive to specific hydrolases.

Conclusions:

• Two distinct glucan classes, alpha-(1 --> 3)-rich and alpha-(1 --> 6)-rich, exist in WT Streptococcus mutans.
• Reduced virulence in mutants is likely due to the inability to form the alpha-(1 --> 3)-rich glucan component.
• Both glucan types are cell-associated and possess complex, polydisperse structures with mixed linkages.