Lei Lei, Yang Yingming, Mao Mengying, Li Hong, Li Meng, Yang Yan, Yin Jiaxin, Hu Tao
State Key Laboratory of Oral Diseases, Department of Operative Dentistry and Endodontics, West China Hospital of Stomatology, Sichuan University Chengdu, China.
Department of Preventive Dentistry, West China Hospital of Stomatology, Sichuan University Chengdu, China.
Front Microbiol. 2015 Dec 21;6:1432. doi: 10.3389/fmicb.2015.01432. eCollection 2015.
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 (1)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 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 (1)H nuclear magnetic resonance spectroscopy) may be useful approaches to determine the roles of other virulence genes for dental caries prevention.
致龋病原体变形链球菌能有效利用膳食蔗糖合成胞外多糖，这些多糖构成其生物膜的支架，从而增强其致病性、环境应激耐受性和抗菌抗性。变形链球菌的双组分系统VicRK调控一组与生物膜基质合成相关的毒力基因。敲除vicX会影响变形链球菌的生物膜形成、氧化应激耐受性和转化能力。然而，关于vicX调控的胞外多糖的结构特征对生物膜形成的影响以及vicX突变体的表型，我们了解得还很少。在此，我们确定了vicX在胞外多糖基质的结构特征和生物膜生理学中的作用。与UA159菌株（变形链球菌野生型菌株）相比，vicX突变体（SmuvicX）生物膜似乎呈现出“荒漠化”，其胞外多糖包裹的细胞簇结构受损。同时，SmuvicX的水不溶性葡聚糖（WIG）合成以及WIG/水溶性葡聚糖（WSG）比值均降低。凝胶渗透色谱（GPC）显示，从SmuvicX生物膜中分离出的WIG分子量远低于UA159菌株，表明多糖链长度存在差异。单糖组成分析证明了vicX基因在葡萄糖代谢中的重要性。我们通过氢核磁共振光谱进行代谢物谱分析，结果显示与UA159菌株相比，SmuvicX生物膜的WSG和WIG中均缺少几个化学位移。因此，vicX对胞外多糖结构特征的调控为胞外多糖结构、基因功能和致龋性之间的相互作用提供了新的见解。我们的结果表明，vicX基因调控与致龋性相关的胞外多糖的结构特征，这可能是一个有助于龋齿防治的潜在靶点。此外，用于纯化变形链球菌生物膜胞外多糖并分析其结构多个方面（GPC、气相色谱 - 质谱联用和氢核磁共振光谱）的方法，可能是确定其他毒力基因在预防龋齿中作用的有用途径。
