Role of extracellular DNA and lipoteichoic acid in the matrix of cariogenic biofilm

Abstract

Dental caries is a costly biofilm-dependent disease that affects children and adults alike worldwide. The assembly of biofilms depends on the formation of an extracellular matrix (ECM). Exopolysaccharides are key components in the ECM while both extracellular DNA (eDNA) and lipoteichoic acids (LTA) are found in high amounts in cariogenic biofilms. Streptococcus mutans orchestrates the biofilm build-up process when dietary carbohydrates are present. Sucrose and starch are substrate and acceptors for exopolysaccharides synthesis by S. mutans exoenzymes present on the pellicle and on bacterial surfaces enabling local accumulation of microbes on the teeth. Over time, these exopolysaccharides build a matrix that embeds the microbial cells forming a cohesive and diffusion-limiting milieu, creating acidic niches where cariogenic organisms thrive and cause acid-dissolution of teeth. In parallel, release of eDNA and LTA by S. mutans is induced by sucrose, starch and increased acidity. Yet, their functional roles in ECM assembly remain poorly understood. We found that sucrose and starch induce the expression of the S. mutans genes lytTS (linked to eDNA), causing assembly of cohesive ECM with high amounts of eDNA and exopolysaccharides. Conversely, the production of S. mutans proteins associated with LTA metabolism (encoded by genes dltABCD and SMU.775) is induced by sucrose in our mixed-species biofilm model. Thus, we hypothesize that eDNA and LTA, acting in concert with exopolysaccharides, impact the assembly, structural organization and functional properties of ECM during biofilm formation. We will address three aims: 1) elucidate the role of eDNA and LTA in the structural and functional properties of ECM; 2) determine the dynamics of S. mutans expression of eDNA and LTA-related genes in a mixed-species cariogenic biofilm model; 3) examine the role of eDNA and LTA in colonization of teeth by S. mutans and biofilm formation in vivo using a rodent model. The studies will provide support for new therapeutic agents aimed at steps (and components) leading to ECM assembly, disrupting formation of biofilms. (AU)