The Exopolysaccharide Matrix Modulates the Interaction between 3D Architecture and Virulence of a Mixed-Species Oral Biofilm

Abstract

Virulent biofilms are responsible for a range of infections, including oral diseases. All biofilms harbor a microbial-derived extracellular-matrix. The exopolysaccharides (EPS) formed on tooth-pellicle and bacterial surfaces provide binding sites for microorganisms; eventually the accumulated EPS enmeshes microbial cells. The metabolic activity of the bacteria within this matrix leads to acidification of the milieu. We explored the mechanisms through which the Streptococcus mutans -produced EPS-matrix modulates the three-dimensional (3D) architecture and the population shifts during morphogenesis of biofilms on a saliva-coated-apatitic surface using a mixed-bacterial species system. Concomitantly, we examined whether the matrix influences the development of pH-microenvironments within intact-biofilms using a novel 3D in situ pH-mapping technique. Data reveal that the production of the EPS-matrix helps to create spatial heterogeneities by forming an intricate network of exopolysaccharide-enmeshed bacterial-islets (microcolonies) through localized cell-to-matrix interactions. This complex 3D architecture creates compartmentalized acidic and EPS-rich microenvironments throughout the biofilm, which triggers the dominance of pathogenic S. mutans within a mixed-species system. The establishment of a 3D-matrix and EPS-enmeshed microcolonies were largely mediated by the S. mutans gtfB/gtfC genes, expression of which was enhanced in the presence of Actinomyces naeslundii and Streptococcus oralis . Acidic pockets were found only in the interiors of bacterial-islets that are protected by EPS, which impedes rapid neutralization by buffer (pH 7.0). As a result, regions of low pH (<5.5) were detected at specific locations along the surface of attachment. Resistance to chlorhexidine was enhanced in cells within EPS-microcolony complexes compared to those outside such structures within the biofilm. Our results illustrate the critical interaction between matrix architecture and pH heterogeneity in the 3D environment. The formation of structured acidic-microenvironments in close proximity to the apatite-surface is an essential factor associated with virulence in cariogenic-biofilms. These observations may have relevance beyond the mouth, as matrix is inherent to all biofilms.

PslG, a self-produced glycosyl hydrolase, triggers biofilm disassembly by disrupting exopolysaccharide matrix

“…Exopolysaccharides are a common component of the extracellular matrix in biofilms formed by many Gram-positive, Gram-negative bacteria and fungus C. albicans [6,[40][41][42]. In this study, we report that PslG, a glycoside hydrolase, prevents the biofilm formation of Pseudomonas species and efficiently disrupts their existing biofilms at nanomolar concentrations.…”

Antimicrobial peptide GH12 suppresses cariogenic virulence factors of Streptococcus mutans

“…GTFB (encoded by gtfB ) produces highly insoluble glucans, which constitute the scaffold of the EPS matrix. GTFC (encoded by gtfC ) catalyzes the formation of a mixture of soluble and insoluble glucans, which shape the initial EPS layers and provide binding sites for S. mutans [1,2,45]. In this study, GH12 at 1/2 MIC exhibited a strong ability to inhibit the synthesis of water-insoluble EPS.…”

Two-component signal transduction systems in oral bacteria

“…Dental biofilms contribute to robust microbial communities organized in a complex extracellular matrix that not only provides a structural scaffold but also protects the biofilm organisms from host and exogenous antimicrobial functions [3,4]. As in most biofilms [5], the composition and structure of the extracellular matrix of dental biofilms are dynamically modulated by the colonizing bacteria in response to local biophysical conditions and the availability of substrates that support its synthesis and other metabolic functions [6]. The biophysical and immunological challenges that affect biofilm formation on oral surfaces are site-specific.…”