Dataset Information

Interspecies competition in oral biofilms mediated by Streptococcus gordonii extracellular deoxyribonuclease SsnA.

ABSTRACT: Extracellular DNA (eDNA) is a key component of many microbial biofilms including dental plaque. However, the roles of extracellular deoxyribonuclease (DNase) enzymes within biofilms are poorly understood. Streptococcus gordonii is a pioneer colonizer of dental plaque. Here, we identified and characterised SsnA, a cell wall-associated protein responsible for extracellular DNase activity of S. gordonii. The SsnA-mediated extracellular DNase activity of S. gordonii was suppressed following growth in sugars. SsnA was purified as a recombinant protein and shown to be inactive below pH 6.5. SsnA inhibited biofilm formation by Streptococcus mutans in a pH-dependent manner. Further, SsnA inhibited the growth of oral microcosm biofilms in human saliva. However, inhibition was ameliorated by the addition of sucrose. Together, these data indicate that S. gordonii SsnA plays a key role in interspecies competition within oral biofilms. Acidification of the medium through sugar catabolism could be a strategy for cariogenic species such as S. mutans to prevent SsnA-mediated exclusion from biofilms.

SUBMITTER: Rostami N

PROVIDER: S-EPMC9744736 | biostudies-literature | 2022 Dec

REPOSITORIES: biostudies-literature

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Interspecies competition in oral biofilms mediated by Streptococcus gordonii extracellular deoxyribonuclease SsnA.

Rostami Nadia N Shields Robert C RC Serrage Hannah J HJ Lawler Catherine C Brittan Jane L JL Yassin Sufian S Ahmed Halah H Treumann Achim A Thompson Paul P Waldron Kevin J KJ Nobbs Angela H AH Jakubovics Nicholas S NS

NPJ biofilms and microbiomes 20221212 1

Extracellular DNA (eDNA) is a key component of many microbial biofilms including dental plaque. However, the roles of extracellular deoxyribonuclease (DNase) enzymes within biofilms are poorly understood. Streptococcus gordonii is a pioneer colonizer of dental plaque. Here, we identified and characterised SsnA, a cell wall-associated protein responsible for extracellular DNase activity of S. gordonii. The SsnA-mediated extracellular DNase activity of S. gordonii was suppressed following growth i ...[more]

PMID: 36509765

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Project description:Extracellular DNA (eDNA) is an important component of biofilm matrix that serves to maintain biofilm structural integrity, promotes genetic exchange within the biofilm, and provides protection against antimicrobial compounds. Advances in microscopy techniques have provided evidence of the cobweb- or lattice-like structures of eDNA within biofilms from a range of environmental niches. However, methods to reliably assess the abundance and architecture of eDNA remain lacking. This study aimed to address this gap by development of a novel, high-throughput image acquisition and analysis platform for assessment of eDNA networks in situ within biofilms. Utilizing Streptococcus gordonii as the model, the capacity for this imaging system to reliably detect eDNA networks and monitor changes in abundance and architecture (e.g., strand length and branch number) was verified. Evidence was provided of a synergy between glucans and eDNA matrices, while it was revealed that surface-bound nuclease SsnA could modify these eDNA structures under conditions permissive for enzymatic activity. Moreover, cross talk between the competence and hexaheptapeptide permease systems was shown to regulate eDNA release by S. gordonii. This novel imaging system can be applied across the wider field of biofilm research, with potential to significantly advance interrogation of the mechanisms by which the eDNA network architecture develops, how it can influence biofilm properties, and how it may be targeted for therapeutic benefit. IMPORTANCE Extracellular DNA (eDNA) is critical for maintaining the structural integrity of many microbial biofilms, making it an attractive target for the management of biofilms. However, our knowledge and targeting of eDNA are currently hindered by a lack of tools for the quantitative assessment of eDNA networks within biofilms. Here, we demonstrate use of a novel image acquisition and analysis platform with the capacity to reliably monitor the abundance and architecture of eDNA networks. Application of this tool to Streptococcus gordonii biofilms has provided new insights into how eDNA networks are stabilized within the biofilm and the pathways that can regulate eDNA release. This highlights how exploitation of this novel imaging system across the wider field of biofilm research has potential to significantly advance interrogation of the mechanisms by which the eDNA network architecture develops, how it can influence biofilm properties, and how it may be targeted for therapeutic benefit.

Project description:Dental caries and periodontitis are the most common oral disease of all age groups, affecting billions of people worldwide. These oral diseases are mostly associated with microbial biofilms in the oral cavity. Streptococcus gordonii, an early tooth colonizing bacterium and Candida albicans, an opportunistic pathogenic fungus, are the two abundant oral microbes that form mixed biofilms with augmented virulence, affecting oral health negatively. Understanding the molecular mechanisms of the pathogen interactions and identifying non-toxic compounds that block the growth of biofilms are important steps in the development of effective therapeutic approaches. In this in vitro study we report the inhibition of mono-species or dual-species biofilms of S. gordonii and C. albicans, and decreased levels of biofilm extracellular DNA (eDNA), when biofilms were grown in the presence of gymnemic acids (GAs), a non-toxic small molecule inhibitor of fungal hyphae. Scanning electron microscopic images of biofilms on saliva-coated hydroxyapatite (sHA) surfaces revealed attachment of S. gordonii cells to C. albicans hyphae and to sHA surfaces via nanofibrils only in the untreated control, but not in the GAs-treated biofilms. Interestingly, C. albicans produced fibrillar adhesive structures from hyphae when grown with S. gordonii as a mixed biofilm; addition of GAs abrogated the nanofibrils and reduced the growth of both hyphae and the biofilm. To our knowledge, this is the first report that C. albicans produces adhesive fibrils from hyphae in response to S. gordonii mixed biofilm growth. Semi-quantitative PCR of selected genes related to biofilms from both microbes showed differential expression in control vs. treated biofilms. Further, GAs inhibited the activity of recombinant S. gordonii glyceraldehyde-3-phosphate dehydrogenase (GAPDH). Taken together, our results suggest that S. gordonii stimulates the expression of adhesive materials in C. albicans by direct interaction and/or signaling, and the adhesive material expression can be inhibited by GAs.

Project description:The interaction of Porphyromonas gingivalis with commensal streptococci promotes P. gingivalis colonization of the oral cavity. We previously showed that a synthetic peptide (BAR) derived from Streptococcus gordonii potently inhibited the formation of P. gingivalis/S. gordonii biofilms (IC50 =1.3 µM) and reduced P. gingivalis virulence in a mouse model of periodontitis. Thus, BAR represents a novel therapeutic to control periodontitis by limiting P. gingivalis colonization of the oral cavity. Here, we sought to develop drug-delivery vehicles for potential use in the oral cavity that comprise BAR-modified poly(lactic-co-glycolic)acid (PLGA) nanoparticles (NPs).PLGA-NPs were initially modified with palmitylated avidin and subsequently conjugated with biotinylated BAR. The extent of BAR modification was quantified using a fluorescent-labeled peptide. Inhibition of P. gingivalis adherence to S. gordonii by BAR-modified NPs was compared with free peptide using a two-species biofilm model.BAR-modified NPs exhibited an average size of 99±29 nm and a more positive surface charge than unmodified NPs (zeta potentials of -7 mV and -25 mV, respectively). Binding saturation occurred when 37 nmol BAR/mg of avidin-NPs was used, which resulted in a payload of 7.42 nmol BAR/mg NPs. BAR-modified NPs bound to P. gingivalis in a dose-dependent manner and more potently inhibited P. gingivalis/S. gordonii adherence and biofilm formation relative to an equimolar amount of free peptide (IC50 of 0.2 µM versus 1.3 µM). BAR-modified NPs also disrupted the preformed P. gingivalis/S. gordonii biofilms more effectively than free peptide. Finally, we demonstrate that BAR-modified NPs promoted multivalent association with P. gingivalis, providing an explanation for the increased effectiveness of NPs.These results indicate that BAR-modified NPs deliver a higher local dose of peptide and may represent a more effective therapeutic approach to limit P. gingivalis colonization of the oral cavity compared to treatment with formulations of free peptide.

Dataset Information

Interspecies competition in oral biofilms mediated by Streptococcus gordonii extracellular deoxyribonuclease SsnA.

Publications

Interspecies competition in oral biofilms mediated by Streptococcus gordonii extracellular deoxyribonuclease SsnA.

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