Effects of Complex DNA and MVs with GTF Extracted from Streptococcus mutans on the Oral Biofilm

Biofilm and bacterial membrane vesicles: recent advances

INTRODUCTION

Bacterial Membrane Vesicles (MVs) play important roles in cell-to-cell communication and transport of several molecules. Such structures are essential components of Extracellular Polymeric Substances (EPS) biofilm matrix of many bacterial species displaying a structural function and a role in virulence and pathogenesis.

AREAS COVERED

In this review were included original articles from the last ten years by searching the keywords 'biofilm' and 'vesicles' on PUBMED and Scopus databases. The articles available in literature mainly describe a positive correlation between bacterial MVs and biofilms formation. The research on Espacenet and Google Patent databases underlines the available patents related to the application of both biofilm MVs and planktonic MVs in inhibiting biofilm formation.

EXPERT OPINION

This review covers and analyzes recent advances in the study of the relationship between bacterial vesicles and biofilm. The huge number of papers discussing the role of MVs confirms the interest aimed at developing new applications in the medical field. The study of the MVs composition and biogenesis may contribute to the identification of components which could be (i) the target for the development of new drugs inhibiting the biofilm establishment; (ii) candidates for the development of vaccines; (iii) biomarkers for the diagnosis of bacterial infections.

Unveiling the complexity of early childhood caries: Candida albicans and Streptococcus mutans cooperative strategies in carbohydrate metabolism and virulence

Objective

To explore the mechanisms underlying the virulence changes in early childhood caries (ECC) caused by Candida albicans (C. albicans) and Streptococcus mutans (S. mutans), with a focus on carbohydrate metabolism and environmental acidification.

Methods

A review of literature was conducted to understand the symbiotic relationship between C. albicans and S. mutans, and their role in the pathogenesis of ECC. The review also examined how their interactions influence carbohydrate metabolism and environmental acidification in the oral cavity.

Results

C. albicans and S. mutans play crucial roles in the onset and progression of ECC. C. albicans promotes the adhesion and accumulation of S. mutans, while S. mutans creates an environment favorable for the growth of C. albicans. Their interactions, especially through carbohydrate metabolism, strengthen their pathogenic potential. The review highlights the importance of understanding these mechanisms for the development of effective management and treatment protocols for ECC.

Conclusion

The symbiotic relationship between C. albicans and S. mutans, and their interactions through carbohydrate metabolism and environmental acidification, are key factors in the pathogenesis of ECC. A comprehensive understanding of these mechanisms is crucial for developing effective strategies to manage and treat ECC.

Bacterial extracellular vesicles: Modulation of biofilm and virulence properties

Microbial pathogens cause persistent infections by forming biofilms and producing numerous virulence factors. Bacterial extracellular vesicles (BEVs) are nanostructures produced by various bacterial species vital for molecular transport. BEVs include various components, including lipids (glycolipids, LPS, and phospholipids), nucleic acids (genomic DNA, plasmids, and short RNA), proteins (membrane proteins, enzymes, and toxins), and quorum-sensing signaling molecules. BEVs play a major role in forming extracellular polymeric substances (EPS) in biofilms by transporting EPS components such as extracellular polysaccharides, proteins, and extracellular DNA. BEVs have been observed to carry various secretory virulence factors. Thus, BEVs play critical roles in cell-to-cell communication, biofilm formation, virulence, disease progression, and resistance to antimicrobial treatment. In contrast, BEVs have been shown to impede early-stage biofilm formation, disseminate mature biofilms, and reduce virulence. This review summarizes the current status in the literature regarding the composition and role of BEVs in microbial infections. Furthermore, the dual functions of BEVs in eliciting and suppressing biofilm formation and virulence in various microbial pathogens are thoroughly discussed. This review is expected to improve our understanding of the use of BEVs in determining the mechanism of biofilm development in pathogenic bacteria and in developing drugs to inhibit biofilm formation by microbial pathogens. STATEMENT OF SIGNIFICANCE: Bacterial extracellular vesicles (BEVs) are nanostructures formed by membrane blebbing and explosive cell lysis. It is essential for transporting lipids, nucleic acids, proteins, and quorum-sensing signaling molecules. BEVs play an important role in the formation of the biofilm's extracellular polymeric substances (EPS) by transporting its components, such as extracellular polysaccharides, proteins, and extracellular DNA. Furthermore, BEVs shield genetic material from nucleases and thermodegradation by packaging it during horizontal gene transfer, contributing to the transmission of bacterial adaptation determinants like antibiotic resistance. Thus, BEVs play a critical role in cell-to-cell communication, biofilm formation, virulence enhancement, disease progression, and drug resistance. In contrast, BEVs have been shown to prevent early-stage biofilm, disperse mature biofilm, and reduce virulence characteristics.

Aspects of oral streptococcal metabolic diversity: Imagining the landscape beneath the fog

It is widely acknowledged that the human-associated microbial community influences host physiology, systemic health, disease progression, and even behavior. There is currently an increased interest in the oral microbiome, which occupies the entryway to much of what the human initially encounters from the environment. In addition to the dental pathology that results from a dysbiotic microbiome, microbial activity within the oral cavity exerts significant systemic effects. The composition and activity of the oral microbiome is influenced by (1) host-microbial interactions, (2) the emergence of niche-specific microbial "ecotypes," and (3) numerous microbe-microbe interactions, shaping the underlying microbial metabolic landscape. The oral streptococci are central players in the microbial activity ongoing in the oral cavity, due to their abundance and prevalence in the oral environment and the many interspecies interactions in which they participate. Streptococci are major determinants of a healthy homeostatic oral environment. The metabolic activities of oral Streptococci, particularly the metabolism involved in energy generation and regeneration of oxidative resources vary among the species and are important factors in niche-specific adaptations and intra-microbiome interactions. Here we summarize key differences among streptococcal central metabolic networks and species-specific differences in how the key glycolytic intermediates are utilized.

Digested extracellular DNA shortens the anodic startup of microbial electrolysis cell

While the multiple functions of extracellular DNA (exDNA) in biofilm formation and electron transfer have been extensively studied in pure culture, its role in mixed anodic biofilm was still unknown. In this study, we employed DNase I enzyme to digest exDNA, thereby investigating its role in anodic biofilm formation based on the performance of four microbial electrolysis cells (MECs) groups with different DNase I enzyme concentration (0, 0.05, 0.1, 0.5 mg/mL). The responding time to reach 60 % maximum current of treatment group with DNase I enzyme has been significantly reduced to 83 %-86 % of the blank group (t-test, p < 0.01), indicating the exDNA digestion could promote the biofilm formation at the early stage. The anodic coulombic efficiency was enhanced by 10.74- 54.42 % in treatment group (t-test, p < 0.05), which could be ascribed to the higher absolute abundance of exoelectrogens. The lower relative abundance of exoelectrogens indicated the DNase I enzyme addition was beneficial for the enrichment of extensive species rather than exoelectrogens. As the DNase I enzyme augments the fluorescence signal of exDNA distribution in the small molecular weight region, implying the short chain exDNA could contribute to the biomass enhancement via boosting the most species enrichment. Furthermore, the exDNA alteration improved the complexity of microbial network. Our findings provide a new insight into the role of exDNA in the extracellular matrix of anodic biofilms.

Interactions between extracellular vesicles and microbiome in human diseases: New therapeutic opportunities

In recent decades, accumulating research on the interactions between microbiome homeostasis and host health has broadened new frontiers in delineating the molecular mechanisms of disease pathogenesis and developing novel therapeutic strategies. By transporting proteins, nucleic acids, lipids, and metabolites in their versatile bioactive molecules, extracellular vesicles (EVs), natural bioactive cell-secreted nanoparticles, may be key mediators of microbiota-host communications. In addition to their positive and negative roles in diverse physiological and pathological processes, there is considerable evidence to implicate EVs secreted by bacteria (bacterial EVs [BEVs]) in the onset and progression of various diseases, including gastrointestinal, respiratory, dermatological, neurological, and musculoskeletal diseases, as well as in cancer. Moreover, an increasing number of studies have explored BEV-based platforms to design novel biomedical diagnostic and therapeutic strategies. Hence, in this review, we highlight the recent advances in BEV biogenesis, composition, biofunctions, and their potential involvement in disease pathologies. Furthermore, we introduce the current and emerging clinical applications of BEVs in diagnostic analytics, vaccine design, and novel therapeutic development.

Identification of the antibacterial action mechanism of curcumin on Streptococcus mutans through transcriptome profiling

OBJECTIVE

The purpose of this study was to explore the effect and mechanism responsible for how curcumin affects the biofilm formation by Streptococcus mutans (S. mutans).

DESIGN

The antibacterial activity of curcumin was evaluated by measuring the minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC). The mass of the biofilm was measured by crystal violet staining. Transcriptome sequencing was used to obtain all the transcript information associated with the biological activity of curcumin-treated S. mutans. Real-time quantitative PCR (qRT-PCR) was performed to examine the expression levels of related biofilm formation genes.

RESULTS

The MIC value for curcumin was 64 μM. Curcumin inhibited the formation of a biofilm by S. mutans and degraded mature biofilms. A gene ontology enrichment analysis showed that the DEGs were significantly relevant to biofilm formation. In addition, 17 significantly enriched Kyoto Encyclopedia of Genes and Genomes pathways (p ≤ 0.01) were identified and were potentially associated with the biochemical metabolic processes of S. mutans. DEGs associated with the biofilm formation of S. mutants, including gtfB, gtfC, rgpG, spaP, spxA1, spxA2, bacA, lrgB, and gshAB. The qRT-PCR results were consistent with transcriptome sequencing that the expression levels of gtfB, gtfC, rgpG, and spaP significantly decreased in the curcumin-treated group, whereas the expression levels of spx1, spx2, bacA, lrgB, and gshAB were up-regulated.

CONCLUSIONS

Curcumin showed marked inhibitory effects against the formation of biofilms by S. mutans and degradation of formed biofilms.

Comparing proteome changes involved in biofilm formation by Streptococcus mutans after exposure to sucrose and starch

Streptococcus mutans is a main organism of tooth infections including tooth decay and periodontitis. The aim of this study was to assess the influence of sucrose and starch on biofilm formation and proteome profile of S. mutans ATCC 35668 strain. The biofilm formation was assessed by microtiter plating method. Changes in bacterial proteins after exposure to sucrose and starch carbohydrates were analyzed using matrix-assisted laser desorption/ionization mass spectrometry. The biofilm formation of S. mutans was increased to 391.76% in 1% sucrose concentration, 165.76% in 1% starch, and 264.27% in the 0.5% sucrose plus 0.5% starch in comparison to biofilm formation in the media without sugars. The abundance of glutamines, adenylate kinase, and 50S ribosomal protein L29 was increased under exposure to sucrose. Upregulation of lactate utilization protein C, 5-hydroxybenzimidazole synthase BzaA, and 50S ribosomal protein L16 was formed under starch exposure. Ribosome-recycling factor, peptide chain release factor 1, and peptide methionine sulfoxide reductase MsrB were upregulated under exposure to sucrose in combination with starch. The results demonstrated that the carbohydrates increase microbial pathogenicity. In addition, sucrose and starch carbohydrates can induce biofilm formation of S. mutans via various mechanisms such as changes in the expression of special proteins.

Streptococcus mutans membrane vesicles inhibit the biofilm formation of Streptococcus gordonii and Streptococcus sanguinis

Streptococcus mutans, whose main virulence factor is glucosyltransferase (Gtf), has a substantial impact on the development of dental caries. S. mutans membrane vesicles (MVs), which are rich in Gtfs, have been shown to affect biofilm formation of other microorganisms. Streptococcus gordonii and Streptococcus sanguinis are initial colonizers of tooth surfaces, which provide attachment sites for subsequent microorganisms and are crucial in the development of oral biofilms. S. mutans and S. gordonii, as well as S. mutans and S. sanguinis, have a complex competitive and cooperative relationship, but it is unclear whether S. mutans MVs play a role in these interspecific interactions. Therefore, we co-cultured S. mutans MVs, having or lacking Gtfs, with S. gordonii and S. sanguinis. Our results showed that S. mutans MVs inhibited biofilm formation of S. gordonii and S. sanguinis but did not affect their planktonic growth; contrastingly, S. mutans ΔgtfBC mutant MVs had little effect on both their growth and biofilm formation. Additionally, there were fewer and more dispersed bacteria in the biofilms of the S. mutans MV-treated group than that in the control group. Furthermore, the expression levels of the biofilm-related virulence factors GtfG, GtfP, and SpxB in S. gordonii and S. sanguinis were significantly downregulated in response to S. mutans MVs. In conclusion, the results of our study showed that S. mutans MVs inhibited biofilm formation of S. gordonii and S. sanguinis, revealing an important role for MVs in interspecific interactions.

New frontiers of oral sciences: Focus on the source and biomedical application of extracellular vesicles

Extracellular vesicles (EVs) are a class of nanoparticles that are derived from almost any type of cell in the organism tested thus far and are present in all body fluids. With the capacity to transfer "functional cargo and biological information" to regulate local and distant intercellular communication, EVs have developed into an attractive focus of research for various physiological and pathological conditions. The oral cavity is a special organ of the human body. It includes multiple types of tissue, and it is also the beginning of the digestive tract. Moreover, the oral cavity harbors thousands of bacteria. The importance and particularity of oral function indicate that EVs derived from oral cavity are quite complex but promising for further research. This review will discuss the extensive source of EVs in the oral cavity, including both cell sources and cell-independent sources. Besides, accumulating evidence supports extensive biomedical applications of extracellular vesicles in oral tissue regeneration and development, diagnosis and treatment of head and neck tumors, diagnosis and therapy of systemic disease, drug delivery, and horizontal gene transfer (HGT). The immune cell source, odontoblasts and ameloblasts sources, diet source and the application of EVs in tooth development and HGT were reviewed for the first time. In conclusion, we concentrate on the extensive source and potential applications offered by these nanovesicles in oral science.

Streptococcus Mutans Membrane Vesicles Enhance Candida albicans Pathogenicity and Carbohydrate Metabolism

Streptococcus mutans and Candida albicans, as the most common bacterium and fungus in the oral cavity respectively, are considered microbiological risk markers of early childhood caries. S. mutans membrane vesicles (MVs) contain virulence proteins, which play roles in biofilm formation and disease progression. Our previous research found that S. mutans MVs harboring glucosyltransferases augment C. albicans biofilm formation by increasing exopolysaccharide production, but the specific impact of S. mutans MVs on C. albicans virulence and pathogenicity is still unknown. In the present study, we developed C. albicans biofilms on the surface of cover glass, hydroxyapatite discs and bovine dentin specimens. The results showed that C. albicans can better adhere to the tooth surface with the effect of S. mutans MVs. Meanwhile, we employed C. albicans biofilm-bovine dentin model to evaluate the influence of S. mutans MVs on C. albicans biofilm cariogenicity. In the S. mutans MV-treated group, the bovine dentin surface hardness loss was significantly increased and the surface morphology showed more dentin tubule exposure and broken dentin tubules. Subsequently, integrative proteomic and metabolomic approaches were used to identify the differentially expressed proteins and metabolites of C. albicans when cocultured with S. mutans MVs. The combination of proteomics and metabolomics analysis indicated that significantly regulated proteins and metabolites were involved in amino acid and carbohydrate metabolism. In summary, the results of the present study proved that S. mutans MVs increase bovine dentin demineralization provoked by C. albicans biofilms and enhance the protein and metabolite expression of C. albicans related to carbohydrate metabolism.

[Research Updates: Cariogenic Mechanism of Streptococcus mutans]

The prevalence of dental caries remains high, posing a major burden on the public health of the global society. Microorganisms are the main cause of dental caries, among which Streptococcus mutans ( S. mutans) is one of the most widely recognized cariogenic bacteria. In recent years, the progress in research technology enabled the academic circle to conduct more in-depth research into caries-inducing S. mutans at the DNA, RNA and protein levels, and to gain thereby a new understanding of the surface structure and extracellular matrix composition of S. mutans. In this paper, we summarized recent findings on the cariogenic mechanism of S. mutans in order to help reveal more targets and potential approaches for the future development of caries prevention agents that target S. mutans, and to promote the development of dental caries prevention campaign.

Understanding the Matrix: The Role of Extracellular DNA in Oral Biofilms

Dental plaque is the key etiological agent in caries formation and the development of the prevalent chronic oral inflammatory disease, periodontitis. The dental plaque biofilm comprises a diverse range of microbial species encased within a rich extracellular matrix, of which extracellular DNA (eDNA) has been identified as an important component. The molecular mechanisms of eDNA release and the structure of eDNA have yet to be fully characterized. Nonetheless, key functions that have been proposed for eDNA include maintaining biofilm structural integrity, initiating adhesion to dental surfaces, acting as a nutrient source, and facilitating horizontal gene transfer. Thus, eDNA is a potential therapeutic target for the management of oral disease–associated biofilm. This review aims to summarize advances in the understanding of the mechanisms of eDNA release from oral microorganisms and in the methods of eDNA detection and quantification within oral biofilms.

Effects of pH on the Properties of Membrane Vesicles Including Glucosyltransferase in Streptococcus mutans

Streptococcus mutans releases membrane vesicles (MVs) and induces MV-dependent biofilm formation. Glucosyltransferases (Gtfs) are bound to MVs and contribute to the adhesion and glucans-dependent biofilm formation of early adherent bacteria on the tooth surface. The biofilm formation of S. mutans may be controlled depending on whether the initial pH tends to be acidic or alkaline. In this study, the characteristics and effects of MVs extracted from various conditions {(initial pH 6.0 and 8.0 media prepared with lactic acid (LA) and acetic acid (AA), and with NaOH (NO), respectively)} on the biofilm formation of S. mutans and early adherent bacteria were investigated. The quantitative changes in glucans between primary pH 6.0 and 8.0 conditions were observed, associated with different activities affecting MV-dependent biofilm formation. The decreased amount of Gtfs on MVs under the initial pH 6.0 conditions strongly guided low levels of MV-dependent biofilm formation. However, in the initial pH 6.0 and 8.0 solutions prepared with AA and NO, the MVs in the biofilm appeared to be formed by the expression of glucans and/or extracellular DNA. These results suggest that the environmental pH conditions established by acid and alkaline factors determine the differences in the local pathogenic activities of biofilm development in the oral cavity.

Molecular mechanisms of inhibiting glucosyltransferases for biofilm formation in Streptococcus mutans

Glucosyltransferases (Gtfs) play critical roles in the etiology and pathogenesis of Streptococcus mutans (S. mutans)- mediated dental caries including early childhood caries. Gtfs enhance the biofilm formation and promotes colonization of cariogenic bacteria by generating biofilm extracellular polysaccharides (EPSs), the key virulence property in the cariogenic process. Therefore, Gtfs have become an appealing target for effective therapeutic interventions that inhibit cariogenic biofilms. Importantly, targeting Gtfs selectively impairs the S. mutans virulence without affecting S. mutans existence or the existence of other species in the oral cavity. Over the past decade, numerous Gtfs inhibitory molecules have been identified, mainly including natural and synthetic compounds and their derivatives, antibodies, and metal ions. These therapeutic agents exert their inhibitory role in inhibiting the expression gtf genes and the activities and secretion of Gtfs enzymes with a wide range of sensitivity and effectiveness. Understanding molecular mechanisms of inhibiting Gtfs will contribute to instructing drug combination strategies, which is more effective for inhibiting Gtfs than one drug or class of drugs. This review highlights our current understanding of Gtfs activities and their potential utility, and discusses challenges and opportunities for future exploration of Gtfs as a therapeutic target.

Structure-function characterization of Streptococcus intermedius surface antigen Pas

Streptococcus intermedius, an oral commensal bacterium, is found at various sites including subgingival dental plaque, purulent infections, and in cystic fibrosis lungs. Oral streptococci utilize proteins on their surface to adhere to tissues and/or surfaces localizing the bacteria, which subsequently leads to the development of biofilms, colonization and infection. Among the 19 genomically annotated cell-wall attached surface proteins on S. intermedius, Pas is an adhesin that belongs to the Antigen I/II (AgI/II) family. Here we have structurally and functionally characterized Pas, particularly focusing on its microbial-host as well as microbial-microbial interactions. The crystal structures of V^Pas and C₁₂₃^Pas show high similarity with AgI/II of S. mutans. V^Pas hosts a conserved metal binding site, and likewise the C₁₂₃^Pas structure retains its conserved metal binding sites and isopeptide bonds within its three DEv-IgG domains. Pas interacts with nanomolar affinity to lung alveolar glycoprotein 340 (Gp340), its scavenger receptor cysteine rich domains (SRCRs) and with fibrinogen. Both Candida albicans and Pseudomonas aeruginosa, the opportunistic pathogens that cohabitate with S. intermedius in the lungs of CFTR patients were studied in dual-species biofilm studies. The Pas deficient mutant (Δpas) displayed significant reduction in dual biofilm formation with C. albicans. In similar studies with P. aeruginosa, Pas did not mediate the biofilm formation with either the acute isolate (PAO1), or the chronic isolate (FRD1). However, the Sortase A deficient mutant (ΔsrtA) displayed reduced biofilm formation with both C. albicans and P. aeruginosa FRD1. Taken together, our findings highlight the role of Pas in both microbial-host and interkingdom interactions and expose its potential role in disease outcomes. Importance Streptococcus intermedius, an oral commensal bacterium, has been clinically observed in subgingival dental plaque, purulent infections, and in cystic fibrosis lungs. In this study, we have (a) determined the crystal structure of the V- and C-regions of Pas; (b) shown that its surface protein Pas adheres to fibrinogen, which could potentially ferry the microbe through the blood stream from the oral cavity; (c) characterized Pas's high affinity adherence to lung alveolar protein Gp340 that could fixate the microbe on lung epithelial cells; and (d) most importantly shown that these surface proteins on the oral commensal S. intermedius enhances biofilms of known pathogens Candida albicans and Pseudomonas aeruginosa.

Characterization and function of membrane vesicles in Gram-positive bacteria

In recent years, extracellular vesicles have gained more attention. However, studies on membrane vesicles in Gram-positive bacteria were carried out relatively late because of the thick bacterial wall and the low production of membrane vesicles. Thanks to the research in recent years, the cognition of the composition and function of the membrane vesicles of Gram-positive bacteria has made significant progress. Membrane vesicles are spherical in shape comprising bilayer membranous structures with a diameter of 20-400 nm. Components of membrane vesicles are diverse, including proteins, nucleic acids, lipids, and metabolites. It also has been reported that membrane vesicles are involved in various pathophysiological processes and serve as communication tools in pathophysiological activities between the bacteria and the host. This review provided the current understanding of components and functions of membrane vesicles in Gram-positive bacteria. The findings might facilitate further research in the emerging field of membrane vesicles in Gram-positive bacteria. KEY POINTS: • Membrane vesicles in Gram-positive bacteria contain proteins, nucleic acids, lipids, and metabolites, suggesting their biological significance. • Membrane vesicles in Gram-positive bacteria are thought to be involved in stress response, biofilm formation, immune regulation, and so on.

The Impacts of Sortase A and the 4'-Phosphopantetheinyl Transferase Homolog Sfp on Streptococcus mutans Extracellular Membrane Vesicle Biogenesis

Extracellular membrane vesicles (EMVs) are produced by many Gram-positive organisms, but information regarding vesiculogenesis is incomplete. We used single gene deletions to evaluate the impacts on Streptococcus mutans EMV biogenesis of Sortase A (SrtA), which affects S. mutans EMV composition, and Sfp, a 4'-phosphopantetheinyl transferase that affects Bacillus subtilis EMV stability. ΔsrtA EMVs were notably larger than Δsfp and wild-type (WT) EMVs. EMV proteins identified from all three strains are known to be involved in cell wall biogenesis and cell architecture, bacterial adhesion, biofilm cell density and matrix development, and microbial competition. Notably, the AtlA autolysin was not processed to its mature active form in the ΔsrtA mutant. Proteomic and lipidomic analyses of all three strains revealed multiple dissimilarities between vesicular and corresponding cytoplasmic membranes (CMs). A higher proportion of EMV proteins are predicted substrates of the general secretion pathway (GSP). Accordingly, the GSP component SecA was identified as a prominent EMV-associated protein. In contrast, CMs contained more multi-pass transmembrane (TM) protein substrates of co-translational transport machineries than EMVs. EMVs from the WT, but not the mutant strains, were enriched in cardiolipin compared to CMs, and all EMVs were over-represented in polyketide flavonoids. EMVs and CMs were rich in long-chain saturated, monounsaturated, and polyunsaturated fatty acids, except for Δsfp EMVs that contained exclusively polyunsaturated fatty acids. Lipoproteins were less prevalent in EMVs of all three strains compared to their CMs. This study provides insight into biophysical characteristics of S. mutans EMVs and indicates discrete partitioning of protein and lipid components between EMVs and corresponding CMs of WT, ΔsrtA, and Δsfp strains.

Streptococcus mutans Membrane Vesicles Harboring Glucosyltransferases Augment Candida albicans Biofilm Development

Candida albicans, as the most common fungus in the oral cavity, is often detected in early childhood caries. Streptococcus mutans is the major etiological agent of dental caries, but the role of S. mutans on C. albicans growth and biofilm development remains to be elucidated. Membrane vesicles (MVs) are a cell-secreted subcellular fraction that play an important role in intercellular communication and disease progression. In the present study, we investigated whether MVs from S. mutans augment C. albicans growth and biofilm development. The results indicated that S. mutans MVs augmented C. albicans biofilm development but had no significant effect on C. albicans growth under planktonic conditions. Subsequently, we labeled S. mutans MVs with PKH26 and used confocal laser scanning microscopy (CLSM) to track S. mutans MVs, which were observed to be located in the C. albicans biofilm extracellular matrix. Monosaccharide tests showed that S. mutans MVs contribute to sucrose metabolism in C. albicans. Polysaccharides were significantly enriched in the S. mutans MV-treated group. MVs from ΔgtfBC mutant strains were compared with those from the wild-type S. mutans. The results revealed that MVs from the ΔgtfBC mutant had no effect on C. albicans biofilm formation and exopolysaccharide production. In addition, C. albicans biofilm transcriptional regulators (Ndt80, Als1, Mnn9, Van1, Pmr1, Gca1, and Big1) expression were upregulated in S. mutans MV-treated group. In summary, the results of the present study showed that S. mutans MVs harboring glucosyltransferases involved in exopolysaccharide production augment C. albicans biofilm development, revealing a key role for S. mutans MVs in cross-kingdom interactions between S. mutans and C. albicans.

Roles of membrane vesicles from Streptococcus mutans for the induction of antibodies to glucosyltransferase in mucosal immunity

Glucosyltransferase (Gtf) B and GtfC from Streptococcus mutans are key enzymes for the development of biofilm-associated diseases such as dental caries. Gtfs are involved in membrane vesicles (MVs) and function in the formation of biofilms by initial colonizers such as Streptococcus mitis and Streptococcus oralis on the tooth surface. Therefore, MVs may be important virulence factors and targets for the prevention of biofilm-associated disease. To clarify how GtfB encoded by gtfB and GtfC encoded by gtfC associate with MVs and whether MVs are effective as a mucosal immunogen to induce the production of antibodies against Gtfs, MVs from S. mutans UA159 wild-type (WT), gtfB^-, gtfC^- and gtfB^-C^- were extracted from culture supernatants by ultracentrifugation and observed by scanning electron microscopy. Compared with GtfB, GtfC was mainly contained in MVs and regulated the size and aggregation of MVs, and the biofilm formation of S. mutans. The intranasal immunization of BALB/c mice with MVs plus a TLR3 agonist, poly(I-C), was performed 2 or 3 times for 5 weeks, with an interval of 2 or 3 weeks. MVs from all strains caused anti-MV IgA and IgG antibody production. In quality analysis of these antibodies, the IgA and IgG antibodies produced by immunization with MVs from WT and gtfB^- strains reacted with Gtfs in the saliva, nasal wash and serum but those produced by immunization with MVs from gtfC^- and gtfB^-C^- strains did not. S. mutans MVs mainly formed by GtfC are an intriguing immunogen for the production of anti-Gtf antibodies in mucosal immunogenicity.