# Water-insoluble exopolysaccharide synthesized by glucosyltransferases mediates the antibacterial activity of ClyR against Streptococcus mutans

## TL;DR

A study shows that a type of sugar molecule produced by a bacteria linked to tooth decay helps a phage enzyme fight the bacteria, suggesting new ways to treat dental caries.

## Contribution

The study reveals a novel mechanism where water-insoluble exopolysaccharides mediate antibacterial activity of ClyR against Streptococcus mutans.

## Key findings

- The ΔgtfB mutant of S. mutans showed increased resistance to ClyR compared to wild-type strains.
- Water-insoluble EPS specifically adsorbed ClyR, with binding localized to the PlyCAC domain.
- EPS synthesized by glucosyltransferases modulates bacterial susceptibility to ClyR.

## Abstract

Dental caries is a widespread global health issue strongly associated with Streptococcus mutans. Bacteriophage-derived lytic enzymes such as ClyR hold considerable promise as antibacterial potential, but the molecular mechanisms underlying their activity against S. mutans remain unclear.

This study aimed to determine the role of water-insoluble exopolysaccharides (EPS) in mediating the antibacterial activity of ClyR against S. mutans.

We compared the antibacterial effects of ClyR on S. mutans UA159 and its ΔgtfB mutant, which is characterized by reduced synthesis of water-insoluble EPS. Biofilm architecture and susceptibility were assessed using scanning electron microscopy, confocal laser scanning microscopy, and biomass quantification. Adsorption assays were conducted to evaluate the interaction between ClyR and water-insoluble EPS.

The ΔgtfB mutant exhibited significantly higher resistance to ClyR than S. mutans UA159, with reduced biofilm disruption and bacterial loss after treatment. In vitro assays confirmed that water-insoluble EPS specifically adsorbed ClyR, with binding localized to its catalytic PlyCAC domain.

Water-insoluble EPS synthesized by S. mutans glucosyltransferases plays a critical role in modulating bacterial susceptibility to ClyR. These findings reveal a novel mechanism underlying bacteriophage lysin activity and highlight EPS as a potential target for enhancing ClyR efficacy against cariogenic biofilms.