Role of sodium in the RprY-dependent stress response in Porphyromonas gingivalis

Modulatory Mechanisms of Pathogenicity in Porphyromonas gingivalis and Other Periodontal Pathobionts

The pathogenesis of periodontitis depends on a sustained feedback loop where bacterial virulence factors and immune responses both contribute to inflammation and tissue degradation. Periodontitis is a multifactorial disease that is associated with a pathogenic shift in the oral microbiome. Within this shift, low-abundance Gram-negative anaerobic pathobionts transition from harmless colonisers of the subgingival environment to a virulent state that drives evasion and subversion of innate and adaptive immune responses. This, in turn, drives the progression of inflammatory disease and the destruction of tooth-supporting structures. From an evolutionary perspective, bacteria have developed this phenotypic plasticity in order to respond and adapt to environmental stimuli or external stressors. This review summarises the available knowledge of genetic, transcriptional, and post-translational mechanisms which mediate the commensal-pathogen transition of periodontal bacteria. The review will focus primarily on Porphyromonas gingivalis.

The efficiency of natural wound healing and bacterial biofilm inhibition of Aloe vera and Sodium Chloride toothpaste preparation

Background

Prevention is a preliminary focus of periodontitis treatment. Rather than giving complicated treatment to a periodontitis patient, a variety of toothpastes have been suggested to prevent periodontal disease progression. Herbal toothpastes containing natural plant components for maintaining or increasing healing might be a treatment modality for improving oral hygiene. Aloe vera is a medicinal plant with active ingredients that have antioxidant and anti-inflammatory effects. Additionally, increased sodium in the environment inhibits microorganism growth. A toothpaste containing salt and aloe vera may be an option to provide good oral hygiene.

Aim

To assess the in vitro cell migration of human gingival fibroblasts and antimicrobial effects of an herbal toothpaste containing A. vera and Sodium chloride.

Methods

The cytotoxicity of 0.02% or 0.2% toothpaste solution on human gingival fibroblast cell line was evaluated using a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay. The cell migration after treatment with 0.2% (v/v) toothpaste was determined using a Boyden Chamber assay. The effect of the toothpaste on inhibiting Porphylomonas gingivalis planktonic and biofilm growth was compared with Chlohexidine (CHX) using a Disk Diffusion and Biofilm susceptibility test, respectively. The results of the cytotoxicity assay, inhibition zone and percentage of live cells in the biofilm were statistically analyzed with One-way analysis of variance. Cell migration and biofilm inhibition were evaluated using the independent sample t-test and multiple t-test, respectively (p = 0.05).

Results

Neither test concentration of the toothpaste solution was toxic to the target cells. The 0.2% concentration was selected for the cell migration experiment. The herbal toothpaste formulation significantly increased cell migration compared with the control group (culture medium) (p = .02) The antimicrobial effect of this formulation on the P. gingivalis planktonic form was lower compared with 0.12% CHX (positive control group), however, it demonstrated greater P. gingivalis biofilm formation inhibition compared with the 0.12% CHX group.

Conclusions

The alternative use of an herbal toothpaste instead of a non-herbal toothpaste formulation should be considered for promoting oral health care. However, further clinical studies are necessary before it can be considered for patient use.

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.

Research progress on two-component signal transduction systems in Porphyromonas gingivalis

Porphyromonas gingivalis (P. gingivalis), a Gram-negative oral anaerobe, is considered to be a major pathogenic agent involved in the onset and progression of chronic periodontitis. P. gingivalis must be able to perceive and respond to the complicated changes in host to survive the environmental challenges, in which the two-component signal transduction systems (TCSs) play critical roles by connecting input signals to cellular physiological output. Canonical TCS consists of a sensor histidine kinase and a cognate response regulator that functions via a phosphorylation cascade. In this review, the roles of TCSs in P. gingivalis were demonstrated by illustrating the target genes and modulation modes, which may help elucidate the underlying mechanisms in future studies.

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.

Porphyromonas gingivalis adopts intricate and unique molecular mechanisms to survive and persist within the host: a critical update

is an obligate, asaccharolytic, gram-negative bacteria commonly associated with increased periodontal and systemic inflammation. P. gingivalis is known to survive and persist within the host tissues as it modulates the entire ecosystem by either engineering its environment or modifying the host's immune response. It interacts with various host receptors and alters signaling pathways of inflammation, complement system, cell cycle, and apoptosis. P. gingivalis is even known to induce suicidal cell death of the host and other microbes in its vicinity with the emergence of pathobiont species. Recently, new molecular and immunological mechanisms and virulence factors of P. gingivalis that increase its chance of survival and immune evasion within the host have been discovered. Thus, the present paper aims to provide a consolidated update on the new intricate and unique molecular mechanisms and virulence factors of P. gingivalis associated with its survival, persistence, and immune evasion within the host.

Global analysis of lysine succinylome in the periodontal pathogen Porphyromonas gingivalis

The gram-negative anaerobe Porphyromonas gingivalis is not only a keystone periodontal pathogen but also an emerging systemic pathogen. Although the newly discovered protein post-translational modification (PTM), lysine succinylation (Ksuc), appears to play an important role in modulating metabolic processes in bacteria, this PTM has not been investigated in P gingivalis. In this study, we used a highly sensitive proteomics approach combining affinity enrichment with high-resolution liquid chromatography coupled with tandem mass spectrometry to examine Ksuc in P gingivalis. In total, 345 Ksuc sites in 233 proteins were identified and determined to be involved in a variety of cellular processes. In the region surrounding Ksuc sites, lysine residues were drastically overrepresented and sequence motifs with succinyl-lysine flanked by a lysine at the +3 or +6 positions appear to be unique to this pathogen. Additionally, our results suggest a crosstalk between Ksuc and glycosylation, but the overlap between Ksuc and acetylation in P gingivalis is quite different from that observed in other organisms. Notably, Ksuc was observed in proteins associated with established virulence factors, including gingipains, fimbriae, RagB, and PorR. Moreover, products of the factors necessary for P gingivalis in vitro survival (18.5%) were found to be succinylated at lysine sites and the same was observed in products of fitness factors for P gingivalis survival in both abscess and epithelial cell colonization environments (12%). Collectively, these results suggest that Ksuc may be a new mechanism in modulating the virulence, adaptation, and fitness of P gingivalis.

Signaling Systems in Oral Bacteria

The supra- and subgingival plaque biofilm communities of plaque are composed of hundreds of different microbes. These communities are spatially and temporally structured, largely due to cell-cell communications that coordinate synergistic interactions, and intracellular signaling systems to sense changes in the surrounding environment. Homeostasis is maintained through metabolic communication, mutualistic cross-feeding, and cross-respiration. These nutritional symbioses can reciprocally influence the local microenvironments by altering the pH and by detoxifying oxidative compounds. Signal transduction mechanisms include two-component systems, tyrosine phosphorelays, quorum sensing systems, and cyclic nucleotide secondary messengers. Signaling converges on transcriptional programs and can result in synergistic or antagonistic interbacterial interactions that sculpt community development. The sum of all these interactions can be a well-organized polymicrobial community that remains in homeostasis with the host, or a dysbiotic community that provokes pathogenic responses in the host.

Post-translational regulation of a Porphyromonas gingivalis regulator

Background: Bacteria use two-component signal transduction systems (among others) to perceive and respond to environmental changes. Within the genus Porphyromonas, we observed degeneration of these systems, as exemplified by the loss of RprX, the sensor kinase partner of the RprY.

Objective: The purpose of this study was to investigate modulation of RprY function by acetylation.

Design: The transcriptional activity of the rprY-pat genes were measured by RT-PCR and 5ʹ-RACE. The acetylation of RprY were detected by western blotting. Electromobility shift and in vitro ChIP assays were used to measure the DNA binding activity of RprY. The expression of RprY target genes was measured by qRT-PCR. Effects of acetylation on phosphorylation of RprY were measured by Phos-tag gels.

Results: The rprY gene is cotranscribed with pat. RprY is acetylated in vivo, and autoacetylated in vitro in a reaction that is enhanced by Pat; the CobB sirtuin deacetylates RprY. Acetylation reduced the DNA binding of RprY. Induced oxidative stress decreased production of RprY in vivo, increased its acetylation and increased expression of nqrA.

Conclusions: We propose that to compensate for the loss of RprX, P. gingivalis has evolved a novel mechanism to inactivate RprY through acetylation.

Two-component signal transduction systems in oral bacteria

We present an overview of how members of the oral microbiota respond to their environment by regulating gene expression through two-component signal transduction systems (TCSs) to support conditions compatible with homeostasis in oral biofilms or drive the equilibrium toward dysbiosis in response to environmental changes. Using studies on the sub-gingival Gram-negative anaerobe Porphyromonas gingivalis and Gram-positive streptococci as examples, we focus on the molecular mechanisms involved in activation of TCS and species specificities of TCS regulons.

A Two-Component System Regulates Bacteroides fragilis Toxin to Maintain Intestinal Homeostasis and Prevent Lethal Disease

Intestinal microbes are recognized for their role in human disease. Enterotoxigenic Bacteroides fragilis (ETBF) has been implicated in inflammatory bowel disease and colorectal cancer; however, colonization alone is insufficient to cause these illnesses. We hypothesized that homeostasis in healthy carriers is maintained by colonic mucus, the major constituent of which is the glycoprotein Muc2. We found that Muc2-deficient mice succumb to lethal disease from ETBF colonization in a B. fragilis toxin (BFT)-dependent manner. We identify a toxin regulator, the two-component system RprXY, which suppresses BFT expression in vitro and in vivo. Overexpression of either component was sufficient to prevent lethal disease in Muc2-deficient mice. Our studies demonstrate that homeostasis in the context of ETBF colonization is dependent on a dynamic interaction between intestinal mucus, a bacterial toxin, and a toxin regulatory system. Regulation of virulence may offer a therapeutic target to maintain intestinal homeostasis in susceptible patients.

Comparative gene expression analysis of Porphyromonas gingivalis ATCC 33277 in planktonic and biofilms states

Background and objective

Porphyromonas gingivalis is a keystone pathogen in the onset and progression of periodontitis. Its pathogenicity has been related to its presence and survival within the subgingival biofilm. The aim of the present study was to compare the genome-wide transcription activities of P. gingivalis in biofilm and in planktonic growth, using microarray technology.

Material and methods

P. gingivalis ATCC 33277 was incubated in multi-well culture plates at 37°C for 96 hours under anaerobic conditions using an in vitro static model to develop both the planktonic and biofilm states (the latter over sterile ceramic calcium hydroxyapatite discs). The biofilm development was monitored by Confocal Laser Scanning Microscopy (CLSM) and Scanning Electron Microscopy (SEM). After incubation, the bacterial cells were harvested and total RNA was extracted and purified. Three biological replicates for each cell state were independently hybridized for transcriptomic comparisons. A linear model was used for determining differentially expressed genes and reverse transcription quantitative polymerase chain reaction (RT-qPCR) was used to confirm differential expression. The filtering criteria of ≥ ±2 change in gene expression and significance p-values of <0.05 were selected.

Results

A total of 92 out of 1,909 genes (4.8%) were differentially expressed by P. gingivalis growing in biofilm compared to planktonic. The 54 up-regulated genes in biofilm growth were mainly related to cell envelope, transport, and binding or outer membranes proteins. Thirty-eight showed decreased expression, mainly genes related to transposases or oxidative stress.

Conclusion

The adaptive response of P. gingivalis in biofilm growth demonstrated a differential gene expression.

Role of extracytoplasmic function sigma factors in biofilm formation of Porphyromonas gingivalis

Background

Porphyromonas gingivalis has been implicated as a major pathogen in the development and progression of chronic periodontitis. P. gingivalis biofilm formation in the subgingival crevice plays an important role in the ability of the bacteria to tolerate stress signals outside the cytoplasmic membrane. Some bacteria use a distinct subfamily of sigma factors to regulate their extracytoplasmic functions (the ECF subfamily). The objective of this study was to determine if P. gingivalis ECF sigma factors affect P. gingivalis biofilm formation.

Methods

To elucidate the role of ECF sigma factors in P. gingivalis, chromosomal mutants carrying a disruption of each ECF sigma factor-encoding gene were constructed. Bacterial growth curves were measured by determining the turbidity of bacterial cultures. The quantity of biofilm growing on plates was evaluated by crystal violet staining.

Results

Comparison of the growth curves of wild-type P. gingivalis strain 33277 and the ECF mutants indicated that the growth rate of the mutants was slightly lower than that of the wild-type strain. The PGN_0274- and PGN_1740-defective mutants had increased biofilm formation compared with the wild-type (p < 0.001); however, the other ECF sigma factor mutants or the complemented strains did not enhance biofilm formation.

Conclusion

These results suggest that PGN_0274 and PGN_1740 play a key role in biofilm formation by P. gingivalis.

Electronic supplementary material

The online version of this article (doi:10.1186/1472-6831-15-4) contains supplementary material, which is available to authorized users.

Identification of genes required for the survival of B. fragilis using massive parallel sequencing of a saturated transposon mutant library

BACKGROUND

Bacteroides fragilis is a Gram-negative anaerobe that is normally a human gut commensal; it comprises a small percentage of the gut Bacteroides but is the most frequently isolated Bacteroides from human infections. Identification of the essential genes necessary for the survival of B. fragilis provides novel information which can be exploited for the treatment of bacterial infections.

RESULTS

Massive parallel sequencing of saturated transposon mutant libraries (two mutant pools of approximately 50,000 mutants each) was used to determine the essential genes for the growth of B. fragilis 638R on nutrient rich medium. Among the 4326 protein coding genes, 550 genes (12.7%) were found to be essential for the survival of B. fragilis 638R. Of the 550 essential genes, only 367 genes were assigned to a Cluster of Orthologous Genes, and about 290 genes had Kyoto Encyclopedia of Genes and Genomes orthologous members. Interestingly, genes with hypothetical functions accounted for 41.3% of essential genes (227 genes), indicating that the functions of a significant percentage of the genes used by B. fragilis 638R are still unknown. Global transcriptome analysis using RNA-Seq indicated that most of the essential genes (92%) are, in fact, transcribed in B. fragilis 638R including most of those coding for hypothetical proteins. Three hundred fifty of the 550 essential genes of B. fragilis 638R are present in Database of Essential Genes. 10.02 and 31% of those are genes included as essential genes for nine species (including Gram-positive pathogenic bacteria).

CONCLUSIONS

The essential gene data described in this investigation provides a valuable resource to study gene function and pathways involved in B. fragilis survival. Thorough examination of the B. fragilis-specific essential genes and genes that are shared between divergent organisms opens new research avenues that will lead to enhanced understanding of survival strategies used by bacteria in different microniches and under different stress situations.