Signaling Systems in Oral Bacteria

Does Streptococcus oralis supernatant influence on the proliferation and virulence of Candida albicans?

OBJECTIVE

To evaluate the influence of Streptococcus oralis supernatant on the proliferation and virulence of Candida albicans.

DESIGN

S. oralis supernatant was obtained by filtration of overnight cultures. Single or dual-species cultures of C. albicans and S. oralis were cultivated in both planktonic and biofilm-based models. Planktonic culture growth was measured, and mature biofilms formed on resin disks were collected to measure biofilm metabolic activity, total biomass, and cell counts. Hyphae formation (virulence factor) and biofilm thickness were analyzed by confocal laser scanning microscopy. Data were analyzed by a one-way ANOVA test followed by the Tukey posthoc test (α = 0.05).

RESULTS

We found that S. oralis supernatant did not influence C. albicans proliferation in planktonic cultures. However, biofilms containing S. oralis supernatant showed higher cell metabolism than C. albicans monoculture biofilms and C. albicans-S. oralis dual-culture biofilms (p < 0.05). Though S. oralis supernatants did increase biofilm metabolic activity, they did not affect the total biomass and cell counts of C. albicans (p > 0.05). However, biofilm imaging revealed enhanced C. albicans hyphae formation in biofilms containing S. oralis supernatant compared to C. albicans monoculture biofilms.

CONCLUSIONS

Secreted metabolites in S. oralis supernatant may contribute to C. albicans metabolism and virulence.

Streptococcus gordonii Poised for Glycan Feeding through a MUC5B-Discriminating, Lipoteichoic Acid-Mediated Outside-In Signaling Circuit

Many oral bacteria employ cell wall-anchored adhesins to bind to the salivary films coating the teeth and mucosal surfaces. Surface binding prevents clearance and facilitates catabolism of salivary film glycoproteins. We asked whether Streptococcus gordonii adhesin expression changes in response to surface salivary cues using a eukaryote-like, outside-in recognition and signaling circuit. To determine whether the cues were discriminated, S. gordonii was tested during cell adhesion and biofilm formation on a MUC5B-rich or lower-molecular-mass salivary fraction or an uncoated abiotic surface. Cells were recovered and analyzed for differences in gene expression and proteins in cell wall fractions. In salivary-free conditions, planktonic S. gordonii presented three prominent cell wall LPXTG-motif proteins, SGO_1487, SGO_0890, and MbpA (mucin-binding protein A; SGO_0707). During biofilm formation on MUC5B-coated surfaces, MbpA, a MUC5B-binding protein, and key genes in the tagatose and quorum-sensing pathways were strongly promoted. The response to MUC5B required the two-component system (TCS), streptococcal regulator of adhesins sensor and regulator (SraSR, SGO_1180/81), lipoteichoic acid (LTA), and the homologous paired adhesins, SspA and SspB (SspAB). LTA appears to link the outside signal (MUC5B) to intramembrane SraSR. Tagatose pathway gene expression may poise cells to metabolize MUC5B glycans and, with a quorum-sensing gene (luxS), may direct formation of a consortium to facilitate glycan cross-feeding by S. gordonii. We now show that a Gram-positive bacterium discriminates specific surface environmental cues using an outside-in signaling mechanism to apparently optimize colonization of saliva-coated surfaces. IMPORTANCE All organisms throughout the tree of life sense and respond to their surface environments. To discriminate among mucosal surface environmental cues, we report that Streptococcus gordonii recognizes a high-molecular-weight mucin glycoprotein, MUC5B, using the paired adhesins SspAB and lipoteichoic acid; the latter bridges the outside signal to an intramembrane two-component system to transcriptionally regulate a MUC5B-specific adhesin and genes that may facilitate glycan catabolism.

Visualized analysis of trends and hotspots in global oral microbiome research: A bibliometric study

The oral microbiome contains numerous bacteria, which directly or indirectly participate in various human functions and continuously exchange signals and substances with the human body, significantly affecting human life cycle, health, and disease. This study aimed to conduct bibliometric studies on the scientific outputs of global oral microbiome research by Citespace software. The data were obtained from the Thomson Reuters' Web of Science Core Collection (WoSCC), from the first relevant literature published until December 31st, 2019, and a total of 2225 articles and reviews were identified. The top country and institutions are the United States and Harvard University. Keywords analysis showed that periodontal disease, oral microbes, and dental plaque are research hotspots. The burst word analysis indicates that early childhood caries, squamous cell carcinoma, gut microbiome, Helicobacter pylori, Candida albicans, and dysbiosis are likely to become the research hotspots of the next era. We also recommend the use of knowledge mapping methods to track specific knowledge areas efficiently and objectively regularly, which can accurately identify hotspots and frontiers and provide valuable information for practitioners in the field, including related scientists, students, journals, and editors.

Identification and characterization of a UbK family kinase in Porphyromonas gingivalis that phosphorylates the RprY response regulator

Phosphorylation of proteins is a key component of bacterial signaling systems that can control important functions such as community development and virulence. We report here the identification of a Ubiquitous bacterial Kinase (UbK) family member, designated UbK1, in the anaerobic periodontal pathogen, Porphyromonas gingivalis. UbK1 contains conserved SPT/S, Hanks-type HxDxYR, EW, and Walker A motifs, and a mutation analysis established the Walker A domain and the Hanks-type domain as required for both autophosphorylation and transphosphorylation. UbK1 autophosphorylates on the proximal serine in the SPT/S domain as well as the tyrosine residue within the HxDxYR domain and the tyrosine residue immediately proximal, indicating both serine/threonine and tyrosine specificity. The orphan two-component system response regulator (RR) RprY was phosphorylated on Y41 in the receiver domain by UbK1. The ubk1 gene is essential in P. gingivalis; however, overexpression of UbK1 showed that UbK1-mediated phosphorylation of RprY functions predominantly to augment its properties as a transcriptional enhancer. These results establish that P. gingivalis possesses an active UbK kinase in addition to a previously described Bacterial Tyrosine family kinase. The RR RprY is identified as the first transcriptional regulator controlled by a UbK enzyme.

Role of the RprY response regulator in P. gingivalis community development and virulence

Porphyromonas gingivalis expresses a limited number of two-component systems, including RprY, an orphan response regulator which lacks a cognate sensor kinase. In this study, we examined cross-phosphorylation of RprY on tyrosine residues and its importance for RprY function. We show that RprY reacts with phosphotyrosine antibodies, and found that the tyrosine (Y) residue at position 41 is predicted to be solvent accessible. Loss of RprY increased the level of heterotypic community development with Streptococcus gordonii, and the community-suppressive function of RprY required Y41. Expression of the Mfa1 fimbrial adhesin was increased in the rprY mutant and in the mutant complemented with rprY containing a Y41F mutation. In a microscale thermophoresis assay, recombinant RprY protein bound to the promoter region of mfa1, and binding was diminished with RprY containing the Y41F substitution. RprY was required for virulence of P. gingivalis in a murine model of alveolar bone loss. Transcriptional profiling indicated that RprY can control the expression of genes encoding the type IX secretion system (T9SS) machinery and virulence factors secreted through the T9SS, including the gingipain proteases and peptidylarginine deiminase (PPAD). Collectively, these results establish the RprY response regulator as a component of the tyrosine phosphorylation regulon in P. gingivalis, which can independently control heterotypic community development through the Mfa1 fimbriae and virulence through the T9SS.

Biodegradable engineered fiber scaffolds fabricated by electrospinning for periodontal tissue regeneration

Considering the specificity of periodontium and the unique advantages of electrospinning, this technology has been used to fabricate biodegradable tissue engineering materials for functional periodontal regeneration. For better biomedical quality, a continuous technological progress of electrospinning has been performed. Based on property of materials (natural, synthetic or composites) and additive novel methods (drug loading, surface modification, structure adjustment or 3 D technique), various novel membranes and scaffolds that could not only relief inflammation but also influence the biological behaviors of cells have been fabricated to achieve more effective periodontal regeneration. This review provides an overview of the usage of electrospinning materials in treatments of periodontitis, in order to get to know the existing research situation and find treatment breakthroughs of the periodontal diseases.

Roles of a Mast Cell-Specific Receptor MRGPRX2 in Host Defense and Inflammation

Mast cells are multifunctional immune cells that are found most abundantly at host-environment interfaces, such as the skin, respiratory tract, and oral/gastrointestinal mucosa. Not surprisingly, mast cells act as sentinel cells that sense microbial attacks and initiate a protective immune response and promote healing. Although mast cells share many features with other innate immune effector cells, such as neutrophils and macrophages, they uniquely interact closely with blood vessels and release an extensive set of mediators for the recruitment of innate and adaptive immune cells. A novel human G protein-coupled receptor (GPCR), known as Mas-related GPCR-X2 (MRGPRX2, mouse ortholog, MrgprB2), has recently been identified, which is expressed on mast cells but not neutrophils and macrophages. Interestingly, activation of MrgprB2 by bacteria-derived quorum-sensing peptides inhibits bacterial growth, prevents biofilm formation, and leads to the recruitment of neutrophils to effectively clear bacteria. Furthermore, host defense antimicrobial peptides and small-molecule peptide mimetics also activate mast cells via MRGPRX2/B2. MrgprB2-mediated activation of local mast cells also clears cutaneous bacterial infection, promotes healing, and protects against reinfection. In addition to their role in host defense, mast cells contribute to a number of chronic inflammatory diseases such as periodontitis, neurogenic inflammation, and inflammatory pain likely via the activation of MRGPRX2. In this review, we discuss the roles of MRGPRX2/B2 in the clearance of bacterial infection, wound healing, periodontal disease, neurogenic inflammation, and inflammatory pain. We propose that harnessing mast cells' host defense and immunomodulatory properties via the activation of MRGPRX2 may lead to novel approaches for the treatment of drug-resistant bacterial infections. On the other hand, increased MRGPRX2 expression on mast cells and their inappropriate activation may contribute to periodontitis, neurogenic inflammation, and inflammatory pain. Thus, targeting MRGPRX2 could provide novel approaches to modulate these conditions.