RgpF Is Required for Maintenance of Stress Tolerance and Virulence in Streptococcus mutans

Area of Science:

• Microbiology
• Bacterial Cell Wall Biology
• Molecular Pathogenesis

Background:

• Streptococcus mutans cell wall composition includes rhamnose-glucose polysaccharides (RGP) linked to peptidoglycan.
• RGP's role in S. mutans physiology, stress tolerance, and virulence is not well understood.
• Rhamnosyltransferases are key enzymes in RGP backbone construction.

Purpose of the Study:

• To investigate the impact of disrupting RGP synthesis by deleting the rhamnosyltransferase gene rgpF.
• To characterize the resulting mutant's cellular physiology, stress tolerance, and virulence.
• To determine the role of RGP in S. mutans aciduricity and pathogenesis.

Main Methods:

• Gene deletion of rgpF in S. mutans to create a mutant strain (ΔrgpF).
• Phenotypic analysis of the ΔrgpF mutant under various stress conditions, including acid challenge.
• Assessment of membrane functions, F1Fo ATPase activity, biofilm formation, and competitive fitness.
• Evaluation of virulence in a Galleria mellonella infection model.

Main Results:

• The ΔrgpF mutant showed reduced overall fitness and heightened sensitivity to stress.
• Acid tolerance was abolished, with disrupted membrane proton gradients and impaired F1Fo ATPase activity.
• Biofilm formation and adherence to hydroxyapatite were significantly reduced.
• In vivo virulence in G. mellonella was significantly attenuated, and competitive fitness was lost.

Conclusions:

• Rhamnose-glucose polysaccharide (RGP) is critical for Streptococcus mutans stress tolerance and virulence.
• Deletion of rgpF severely compromises S. mutans cell wall integrity and function.
• RGP plays a vital role in aciduricity, biofilm formation, and pathogenesis, representing a potential therapeutic target.