Molecular Oral Microbiology最新文献

Objectives: The study aimed to evaluate the role of Streptococcus mutans (S. mutans) dexA gene on biofilm structure and microecological distribution in multispecies biofilms.

Materials and methods: A multispecies biofilm model consisting of S. mutans and its dexA mutants, Streptococcus gordonii (S. gordonii) and Streptococcus sanguinis (S. sanguinis) was constructed, and bacterial growth, biofilm architecture and microbiota composition were determined to study the effect of the S. mutans dexA on multispecies biofilms.

Results: Our results showed that either deletion or overexpression of S. mutans dexA had no effect on the planktonic growth of bacterium, while S. mutans dominated in the multispecies biofilms to form cariogenic biofilms. Furthermore, we revealed that the SmudexA+ group showed structural abnormality in the form of more fractures and blank areas. The morphology of the SmudexA group was sparser and more porous, with reduced and less agglomerated exopolysaccharides scaffold. Interestingly, the microbiota composition analysis provided new insights that the inhibition of S. gordonii and S. sanguinis was alleviated in the SmudexA group compared to the significantly suppressed condition in the other groups.

Conclusion: In conclusion, deletion of S. mutans dexA gene re-modules biofilm structure and microbiota composition, thereby leading to decreased cariogenicity. Thus, the S. mutans dexA may be an important target for regulating the cariogenicity of dental plaque biofilms, expecting to be a probiotic for caries control.

Porphyromonas gingivalis is an anaerobic Gram-negative human oral pathogen highly associated with the more severe forms of periodontal disease. Porphyromonas gingivalis utilises the type IX secretion system (T9SS) to transport ∼30 cargo proteins, including multiple virulence factors, to the cell surface. The T9SS is a multiprotein system consisting of at least 20 proteins, and recently, we characterised the protein interactome of these components. Similar to the T9SS, almost all biological processes are mediated through protein-protein interactions (PPIs). Therefore, mapping PPIs is important to understand the biological functions of many proteins in P. gingivalis. Herein, we provide native migration profiles of over 1000 P. gingivalis proteins. Using the T9SS, we demonstrate that our dataset is a useful resource for identifying novel protein interactions. Using this dataset and further analysis of T9SS P. gingivalis mutants, we discover new mechanistic insights into the formation of the PorQ-Z complex of the T9SS. This dataset is a valuable resource for studies of P. gingivalis.

Aggregatibacter actinomycetemcomitans, a Gram-negative oral pathobiont causing aggressive periodontitis and systemic infections, demonstrates serum resistance. We have identified a dsDNA-tailed bacteriophage, S1249, which was found to convert from this microorganism inducible by human serum into a lytic state to kill the bacterium. This phage demonstrated active transcripts when exposed to human serum: 20% of genes were upregulated more than 10-fold, and 45% of them were upregulated 5-10-fold when the bacterium was grown in the presence of human serum compared to without the presence of human serum. Transcriptional activation when grown in equine serum was less pronounced. This phage demonstrated a tail with inner rigid tubes and an outer contractile sheath, features of Myoviridae spp. Further characterization revealed that the lysogenized integration of the phage in the chromosome of A. actinomycetemcomitans occurred between the genes encoding cold-shock DNA-binding domain-containing protein (csp) and glutamyl-tRNA synthetase (gltX). Both phage DNA integrated lysogeny and nonintegrated pseudolysogeny were identified in the infected bacterium. A newly generated, lysogenized strain using this phage displayed similar attributes, including 63% growth inhibition compared to its isogenic phage-free strain when in the presence of human serum. Our data suggest that bacteriophage S1249 can be induced in the presence of human serum and enters the lytic cycle, which reduces the viability of infected bacteria in vivo.

Squamous cell carcinoma is the most common malignant tumor of the oral cavity and its adjacent sites, which endangers the physical and mental health of patients and has a complex etiology. Chronic infection is considered to be a risk factor in cancer development. Evidence suggests that periodontal pathogens, such as Porphyromonas gingivalis, Fusobacterium nucleatum, and Treponema denticola, are associated with oral squamous cell carcinoma (OSCC). They can stimulate tumorigenesis by promoting epithelial cells proliferation while inhibiting apoptosis and regulating the inflammatory microenvironment. Candida albicans promotes OSCC progression and metastasis through multiple mechanisms. Moreover, oral human papillomavirus (HPV) can induce oropharyngeal squamous cell carcinoma (OPSCC). There is evidence that HPV16 can integrate with host cells' DNA and activate oncogenes. Additionally, oral dysbiosis and synergistic effects in the oral microbial communities can promote cancer development. In this review, we will discuss the biological characteristics of oral microbiome associated with OSCC and OPSCC and then highlight the mechanisms by which oral microbiome is involved in oral oncogenesis, tumor progression, and metastasis. These findings may have positive implications for early diagnosis and treatment of oral cancer.

Outer membrane vesicles (OMVs) of bacteria harbor physiologically active molecules, and quorum sensing inhibitors (QSIs) are expected to regulate bacterial virulence. In this study, we analyzed the proinflammatory activity of OMVs of the periodontal pathogen Tannerella forsythia treated with d-arabinose and d-galactose as QSIs, which inhibit the biofilm formation of periodontal pathogens and autoinducer 2 activity. Compared to OMVs of nontreated T. forsythia (TF OMVs), OMVs released from QSI-treated T. forsythia, designated TF ara-OMVs and TF gal-OMVs, showed reduced production of TNF-α, IL-1β, IL-6, and IL-8 in THP-1 monocytes through decreased activation of NF-κB/MAPKs. Using a human NF-κB reporter cell line and bone marrow-derived macrophages from TLR2^-/- mice, TF ara-OMVs and TF gal-OMVs showed less activation of TLR2 than TF OMVs. These results demonstrated that QSIs provide a dual advantage against bacterial infection by inhibiting bacterial biofilm formation and generating OMVs with reduced proinflammatory activity.

The survival/adaptation of Filifactor alocis, a fastidious Gram-positive asaccharolytic anaerobe, to the inflammatory environment of the periodontal pocket requires an ability to overcome oxidative stress. Moreover, its pathogenic characteristics are highlighted by its capacity to survive in the oxidative-stress microenvironment of the periodontal pocket and a likely ability to modulate the microbial community dynamics. There is still a significant gap in our understanding of its mechanism of oxidative stress resistance and its impact on the virulence and pathogenicity of the microbial biofilm. Coinfection of epithelial cells with F. alocis and Porphyromonas gingivalis resulted in the upregulation of several genes, including HMPREF0389_01654 (FA1654). Bioinformatics analysis indicates that FA1654 has a "di-iron binding domain" and could function as a DNA starvation and stationary phase protection (DPS) protein. We have further characterized the FA1654 protein to determine its role in oxidative stress resistance in F. alocis. In the presence of hydrogen peroxide-induced oxidative stress, there was an ∼1.3 fold upregulation of the FA1654 gene in F. alocis. Incubation of the purified FA1654 protein with DNA in the presence of hydrogen peroxide and iron resulted in the protection of the DNA from Fenton-mediated degradation. Circular dichroism and differential scanning fluorimetry studies have documented the intrinsic ability of rFA1654 protein to bind iron; however, the rFA1654 protein is missing the intrinsic ability to reduce hydrogen peroxide. Collectively, the data may suggest that FA1654 in F. alocis is involved in oxidative stress resistance via an ability to protect against Fenton-mediated oxidative stress-induced damage.

The Porphyromonas gingivalis Mfa1 fimbria is composed of the Mfa1 to Mfa5 proteins, encoded by the mfa1 to mfa5 genes, respectively, which are tandemly arranged on chromosomes. A recent study discovered that many P. gingivalis strains possess two mfa5 genes (called herein mfa5-1 and mfa5-2), which are also in tandem. This study examined the transcriptional unit and activity of mfa-cluster genes in strains with one (the ATCC 33277 and TDC60 strains) and two (the HG66 and A7436 strains) mfa5 genes. Complementary DNA was prepared from the total RNA extracted from the bacterial cells in the logarithmic growth phase using a random primer. PCR analysis for the intergenic regions from mfa1 to mfa5 or mfa5-2 showed that mfa1 to mfa5 or mfa5-2 formed a polycistronic gene cluster. Quantitative real-time PCR showed that the mfa1 transcription was 5-10 times higher than that of mfa2 in all the strains. However, mfa2 to mfa5 mostly showed a comparable expression. Both mfa5 genes were comparably transcribed in HG66 and A7436 strains. The transcriptional levels were almost consistent with the respective protein expression levels. In silico analysis identified a transcriptional terminator structure in the intergenic region between mfa1 and mfa2 that was probably responsible for the decreased transcription rate of mfa2 and the downstream genes.

Dental caries is a chronic progressive disease, which destructs dental hard tissues under the influence of multiple factors, mainly bacteria. Streptococcus mutans is the main cariogenic bacteria. However, its cariogenic virulence is affected by environmental stress such as oxidative stress, nutrient deficiency, and low pH to some extent. Oxidative stress is one of the main stresses that S. mutans faces in oral cavity. But there are a variety of protective molecules to resist oxidative stress in S. mutans, including superoxide dismutase, nicotinamide adenine dinucleotide oxidase, Dps-like peroxide resistance protein, alkyl-hydrogen peroxide reductase, thioredoxin, glutamate-reducing protein system, and some metabolic substances. Additionally, some transcriptional regulatory factors (SloR, PerR, Rex, Spx, etc.) and two-component systems are also closely related to oxidative stress adaptation by modulating the expression of protective molecules. This review summarizes the research progress of protective molecules and regulatory mechanisms (mainly transcription factors) of oxidative stress adaptation of S. mutans.

Porphyromonas gingivalis is a keystone pathogen for periodontitis. The function of the GntR family transcription factor is poorly studied in P. gingivalis. Numerous processes govern bacterial growth. The survival and pathogenicity of P. gingivalis depend heavily on its capacity to acquire amino acids as nutritional sources. In this investigation, a GntR transcription factor, pg1007, was identified in P. gingivalis, the deletion of which significantly inhibited bacterial growth. The mutant strain also exhibited an increased extracellular activity of gingipains and acylpeptidyl oligopeptidase (AOP). Global gene expression profiling revealed that the expression levels of 59 genes were significantly altered in the Δpg1007 mutant, with an upregulation in gene expression for AOP, ABC transporters, and some membrane proteins. In addition, His-PG1007 protein was purified as a recombinant protein from Escherichia coli, and the conserved DNA sequence bound by it was determined using electrophoretic mobility shift assays and DNase I footprinting assays. Consequently, this study demonstrated that pg1007 is a crucial transcription factor in P. gingivalis and regulates the bacterial growth and activity of gingipains and AOP. These findings may enhance our understanding of the regulation of bacterial proliferation and protease activity in P. gingivalis.

A detailed understanding of where bacteria localize is necessary to advance microbial ecology and microbiome-based therapeutics. The site-specialist hypothesis predicts that most microbes in the human oral cavity have a primary habitat type within the mouth where they are most abundant. We asked whether this hypothesis accurately describes the distribution of the members of the genus Streptococcus, a clinically relevant taxon that dominates most oral sites. Prior analysis of 16S rRNA gene sequencing data indicated that some oral Streptococcus clades are site-specialists while others may be generalists. However, within complex microbial populations composed of numerous closely related species and strains, such as the oral streptococci, genome-scale analysis is necessary to provide the resolution to discriminate closely related taxa with distinct functional roles. Here, we assess whether individual species within this genus are specialists using publicly available genomic sequence data that provide species-level resolution. We chose a set of high-quality representative genomes for human oral Streptococcus species. Onto these genomes, we mapped shotgun metagenomic sequencing reads from supragingival plaque, tongue dorsum, and other sites in the oral cavity. We found that every abundant Streptococcus species in the healthy human oral cavity showed strong site-tropism and that even closely related species such as S. mitis, S. oralis, and S. infantis specialized in different sites. These findings indicate that closely related bacteria can have distinct habitat distributions in the absence of dispersal limitation and under similar environmental conditions and immune regimes. Substantial overlap between the core genes of these three species suggests that site-specialization is determined by subtle differences in genomic content.