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

TITLE=Modulation of Biofilm Exopolysaccharides by the Streptococcus mutans vicX Gene

JOURNAL=Frontiers in Microbiology

VOLUME=6

YEAR=2015

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2015.01432

DOI=10.3389/fmicb.2015.01432

ISSN=1664-302X

ABSTRACT=<p>The cariogenic pathogen <italic>Streptococcus mutans</italic> 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 <italic>VicRK</italic> of <italic>S. mutans</italic> regulates a group of virulence genes that are associated with biofilm matrix synthesis. Knockout of <italic>vicX</italic> affects biofilm formation, oxidative stress tolerance, and transformation of <italic>S. mutans</italic>. However, little is known regarding the <italic>vicX</italic>-modulated structural characteristics of the exopolysaccharides underlying the biofilm formation and the phenotypes of the <italic>vicX</italic> mutants. Here, we identified the role of <italic>vicX</italic> in the structural characteristics of the exopolysaccharide matrix and biofilm physiology. The <italic>vicX</italic> mutant (SmuvicX) biofilms seemingly exhibited “desertification” with architecturally impaired exopolysaccharide-enmeshed cell clusters, compared with the UA159 strain (<italic>S. mutans</italic> 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 <italic>vicX</italic> gene in the glucose metabolism. We performed metabolite profiling via <sup>1</sup>H 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 <italic>vicX</italic> provides new insights into the interaction between the exopolysaccharide structure, gene functions, and cariogenicity. Our results suggest that <italic>vicX</italic> 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 <italic>S. mutans</italic> biofilms and to analyze multiple aspects of its structure (GPC, gas chromatography-mass spectrometry, and <sup>1</sup>H nuclear magnetic resonance spectroscopy) may be useful approaches to determine the roles of other virulence genes for dental caries prevention.</p>