Modulation of Biofilm Exopolysaccharides by the Streptococcus mutans vicX Gene.

Lei Lei,Meng Li,Mengying Mao,Hong Li,Jiaxin Yin,Tao Hu,Yingming Yang,Yan Yang

doi:10.3389/fmicb.2015.01432

Lei Lei, Meng Li + Show 6 more

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https://doi.org/10.3389/fmicb.2015.01432

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Abstract

The cariogenic pathogen Streptococcus mutans effectively utilizes dietary sucrose for the synthesis of exopolysaccharide, which act as a scaffold for its biofilm, thus contributing to its pathogenicity, environmental stress tolerance, and antimicrobial resistance. The two-component system VicRK of S. mutans regulates a group of virulence genes that are associated with biofilm matrix synthesis. Knockout of vicX affects biofilm formation, oxidative stress tolerance, and transformation of S. mutans. However, little is known regarding the vicX-modulated structural characteristics of the exopolysaccharides underlying the biofilm formation and the phenotypes of the vicX mutants. Here, we identified the role of vicX in the structural characteristics of the exopolysaccharide matrix and biofilm physiology. The vicX mutant (SmuvicX) biofilms seemingly exhibited “desertification” with architecturally impaired exopolysaccharide-enmeshed cell clusters, compared with the UA159 strain (S. mutans wild type strain). Concomitantly, SmuvicX showed a decrease in water-insoluble glucan (WIG) synthesis and in WIG/water-soluble glucan (WSG) ratio. Gel permeation chromatography (GPC) showed that the WIG isolated from the SmuvicX biofilms had a much lower molecular weight compared with the UA159 strain indicating differences in polysaccharide chain lengths. A monosaccharide composition analysis demonstrated the importance of the vicX gene in the glucose metabolism. We performed metabolite profiling via 1H nuclear magnetic resonance spectroscopy, which showed that several chemical shifts were absent in both WSG and WIG of SmuvicX biofilms compared with the UA159 strain. Thus, the modulation of structural characteristics of exopolysaccharide by vicX provides new insights into the interaction between the exopolysaccharide structure, gene functions, and cariogenicity. Our results suggest that vicX gene modulates the structural characteristics of exopolysaccharide associated with cariogenicity, which may be explored as a potential target that contributes to dental caries management. Furthermore, the methods used to purify the EPS of S. mutans biofilms and to analyze multiple aspects of its structure (GPC, gas chromatography-mass spectrometry, and 1H nuclear magnetic resonance spectroscopy) may be useful approaches to determine the roles of other virulence genes for dental caries prevention.

Highlights

Dental plaque as a microbial biofilm is defined as the multispecies community of micro-organisms formed on tooth surfaces (Kroes et al, 1999)
Glucans, including water-insoluble glucan (WIG) and water-soluble glucan (WSG), undergo structural modifications resulting from the effects of glucosyltransferases (Gtfs) and fructosyltransferase (Ftf; Rolla et al, 1983), together with dextranase (Dex), a type of glucanase that participates in the degradation of exopolysaccharide (Khalikova et al, 2003), during glucan synthesis
We focused on the ecological role of vicX gene in the structural characteristics of exopolysaccharide that are associated with cariogenicity

Summary

Introduction

Dental plaque as a microbial biofilm is defined as the multispecies community of micro-organisms formed on tooth surfaces (Kroes et al, 1999). Streptococcus mutans (S. mutans) is among the few species that have been consistently linked with caries formation, with the ability to synthesize extracellular polysaccharides that promote formation of the plaque biofilm, and contributes to the pathogenicity of the species (Yamashita et al, 1993; Xiao and Koo, 2010). Glucans, including water-insoluble glucan (WIG) and water-soluble glucan (WSG), undergo structural modifications resulting from the effects of glucosyltransferases (Gtfs) and fructosyltransferase (Ftf; Rolla et al, 1983), together with dextranase (Dex), a type of glucanase that participates in the degradation of exopolysaccharide (Khalikova et al, 2003), during glucan synthesis. Dex degrades glucans by hydrolyzing the glycosidic bonds and inhibits Gtf activity (Khalikova et al, 2003)

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