OxyR is involved in coordinate regulation of expression of fimA and sod genes in Porphyromonas gingivalis

Extracellular Vesicles of Porphyromonas gingivalis Disrupt Trophoblast Cell Interaction with Vascular and Immune Cells in an In Vitro Model of Early Placentation

Extracellular vesicles released by the primary pathogen of periodontal disease Porphyromonas gingivalis (Pg), referred to as outer membrane vesicles (OMVs), have been associated with the pathogenesis of systemic diseases like cardiovascular disease, rheumatoid arthritis, and Alzheimer's disease. A pathogenic role for Pg by disrupting placental homeostasis was proposed in the association between periodontal disease and adverse pregnancy outcomes. On the basis that trophoblast-derived factors modulate endothelial and immune cell profiles in normal pregnancy and the scarce presence of Pg in placenta, we hypothesized that OMVs from Pg affect trophoblast cell phenotype, impairing trophoblast-endothelium and trophoblast-neutrophil interactions. By means of in vitro designs with first-trimester human trophoblast cells, endothelial cells, and freshly isolated neutrophils, we showed that Pg OMVs are internalized by trophoblast cells and modulate the activity and expression of functional markers. Trophoblast cells primed with Pg OMVs enhanced neutrophil chemoattraction and lost their anti-inflammatory effect. In addition, reduced migration with enhanced adhesion of monocytes was found in endothelial cells upon incubation with the media from trophoblast cells pretreated with Pg OMVs. Taken together, the results support a pathogenic role of Pg OMVs at early stages of pregnancy and placentation through disruption of trophoblast contribution to vascular transformation and immune homeostasis maintenance.

A Novel Injectable Piezoelectric Hydrogel for Periodontal Disease Treatment

Periodontal disease is a multifactorial, bacterially induced inflammatory condition characterized by the progressive destruction of periodontal tissues. The successful nonsurgical treatment of periodontitis requires multifunctional technologies offering antibacterial therapies and promotion of bone regeneration simultaneously. For the first time, in this study, an injectable piezoelectric hydrogel (PiezoGEL) was developed after combining gelatin methacryloyl (GelMA) with biocompatible piezoelectric fillers of barium titanate (BTO) that produce electrical charges when stimulated by biomechanical vibrations (e.g., mastication, movements). We harnessed the benefits of hydrogels (injectable, light curable, conforms to pocket spaces, biocompatible) with the bioactive effects of piezoelectric charges. A thorough biomaterial characterization confirmed piezoelectric fillers' successful integration with the hydrogel, photopolymerizability, injectability for clinical use, and electrical charge generation to enable bioactive effects (antibacterial and bone tissue regeneration). PiezoGEL showed significant reductions in pathogenic biofilm biomass (∼41%), metabolic activity (∼75%), and the number of viable cells (∼2-3 log) compared to hydrogels without BTO fillers in vitro. Molecular analysis related the antibacterial effects to be associated with reduced cell adhesion (downregulation of porP and fimA) and increased oxidative stress (upregulation of oxyR) genes. Moreover, PiezoGEL significantly enhanced bone marrow stem cell (BMSC) viability and osteogenic differentiation by upregulating RUNX2, COL1A1, and ALP. In vivo, PiezoGEL effectively reduced periodontal inflammation and increased bone tissue regeneration compared to control groups in a mice model. Findings from this study suggest PiezoGEL to be a promising and novel therapeutic candidate for the treatment of periodontal disease nonsurgically.

Effect of yhfS gene on Bt LLP29 antioxidant and UV ray resistance

BACKGROUND

Bacillus thuringiensis (Bt) is a widely used microbial insecticide. However, its persistence is limited because of ultraviolet (UV) rays or other environmental factors. The yhfS gene, which encodes acetyl-CoA acyltransferase, plays an important role in lipid transport and metabolism in many organisms. To explore whether it is related to the stress resistance of Bt LLP29, the yhfS gene knockout strain LLP29 Δ-yhfS and the complementary strain LLP29 R-yhfS were generated successfully by homologous recombination technology, and the related phenotypic changes were compared in this study.

RESULTS

Gene yhfS was found to be functional in response to UV radiation in Bt by comparing the survival rates of Bt LLP29 harboring yhfS or not under UV light. Enzyme activity assays of key enzymes showed the the Embden-Meyerhof-Parnas pathway was enhanced yet the tricarboxylic acid cycle as well as butanoate synthesis were repressed when the gene was deleted. At the same time, the amino acid content was decreased, but reduced nicotinamide adenine dinucleotide (NADH) and reactive oxygen species (ROS) content were increased. Most noteworthy, antioxidase (such as superoxide dismutase and peroxidase) activities and contents of some potent antioxidants (such as pyruvate, carotenoids and NADPH) were lower in LLP29 Δ-yhfS than in LLP29.

CONCLUSION

These tests revealed that the loss of the yhfS gene led to metabolic disorders and reduction of the antioxidant ability of Bt. Higher ROS level and lower anti-oxidative capacity might be responsible for the reduced UV resistance when the gene was deleted. These results not only greatly enrich understanding of the mechanism of Bt UV resistance, but also provide an important theoretical basis for Bt application. © 2023 Society of Chemical Industry.

Ucl fimbriae regulation and glycan receptor specificity contribute to gut colonisation by extra-intestinal pathogenic Escherichia coli

Extra-intestinal pathogenic Escherichia coli (ExPEC) belong to a critical priority group of antibiotic resistant pathogens. ExPEC establish gut reservoirs that seed infection of the urinary tract and bloodstream, but the mechanisms of gut colonisation remain to be properly understood. Ucl fimbriae are attachment organelles that facilitate ExPEC adherence. Here, we investigated cellular receptors for Ucl fimbriae and Ucl expression to define molecular mechanisms of Ucl-mediated ExPEC colonisation of the gut. We demonstrate differential expression of Ucl fimbriae in ExPEC sequence types associated with disseminated infection. Genome editing of strains from two common sequence types, F11 (ST127) and UTI89 (ST95), identified a single nucleotide polymorphism in the ucl promoter that changes fimbriae expression via activation by the global stress-response regulator OxyR, leading to altered gut colonisation. Structure-function analysis of the Ucl fimbriae tip-adhesin (UclD) identified high-affinity glycan receptor targets, with highest affinity for sialyllacto-N-fucopentose VI, a structure likely to be expressed on the gut epithelium. Comparison of the UclD adhesin to the homologous UcaD tip-adhesin from Proteus mirabilis revealed that although they possess a similar tertiary structure, apart from lacto-N-fucopentose VI that bound to both adhesins at low-micromolar affinity, they recognize different fucose- and glucose-containing oligosaccharides. Competitive surface plasmon resonance analysis together with co-structural investigation of UcaD in complex with monosaccharides revealed a broad-specificity glycan binding pocket shared between UcaD and UclD that could accommodate these interactions. Overall, our study describes a mechanism of adaptation that augments establishment of an ExPEC gut reservoir to seed disseminated infections, providing a pathway for the development of targeted anti-adhesion therapeutics.

ExPEC infection of the urinary tract and bloodstream is frequently seeded from an intestinal reservoir, necessitating an understanding of the mechanisms that promote gut colonisation. Here we employed molecular and structural approaches to define the regulation and function of ExPEC Ucl fimbriae as a gut colonisation factor. We describe how mutations in the non-coding regulatory region of the ucl promoter cause increased Ucl fimbriae expression and promote enhanced gut colonisation via tuned induction by a global regulator that senses oxygen stress. We further define the glycan receptor targets of Ucl fimbriae and characterise the structural features of the Ucl adhesin that facilitate these interactions. These findings explain how ExPEC can adapt to survival in the gut to seed extra-intestinal infection.

Direct current exerts electricidal and bioelectric effects on Porphyromonas gingivalis biofilms partially via promoting oxidative stress and antibiotic transport

Low electric current can inhibit certain microbial biofilms and enhance the efficacy of antimicrobials against them. This study investigated the electricidal and bioelectric effects of direct current (DC) against Porphyromonas gingivalis biofilms as well as the underlying mechanisms. Here, we firstly showed that DC significantly suppressed biofilm formation of P. gingivalis in time- and intensity-dependent manners, and markedly inhibited preformed P. gingivalis biofilms. Moreover, DC enhanced the killing efficacy of metronidazole (MTZ) and amoxicillin with clavulanate potassium (AMC) against the biofilms. Notably, DC-treated biofilms displayed upregulated intracellular ROS and expression of ROS related genes (sod, feoB, and oxyR) as well as porin gene. Interestingly, DC-induced killing of biofilms was partially reversed by ROS scavenger N-dimethylthiourea (DMTU), and the synergistic effect of DC with MTZ/AMC was weakened by small interfering RNA of porin gene (si-Porin). In conclusion, DC can exert electricidal and bioelectric effects against P. gingivalis biofilms partially via promotion of oxidative stress and antibiotic transport, which offers a promising approach for effective management of periodontitis.

OxyR inactivation reduces the growth rate and oxidative stress defense in Capnocytophaga ochracea

OBJECTIVE

The human oral cavity harbors several bacteria. Among them, Capnocytophaga ochracea, a facultative anaerobe, is responsible for the early phase of dental plaque formation. In this phase, the tooth surface or tissue is exposed to various oxidative stresses. For colonization in the dental plaque phase, a response by hydrogen peroxide (H₂O₂)-sensing transcriptional regulators, such as OxyR, may be necessary. However, to date, no study has elucidated the role of OxyR protein in C. ochracea.

METHODS

Insertional mutagenesis was used to create an oxyR mutant, and gene expression was evaluated by reverse transcription-polymerase chain reaction and quantitative real-time reverse transcription-polymerase chain reaction. Bacterial growth curves were generated by turbidity measurement, and the sensitivity of the oxyR mutant to H₂O₂ was assessed using the disc diffusion assay. Finally, a two-compartment system was used to assess biofilm formation.

RESULTS

The oxyR mutant grew slower than the wild-type under anaerobic conditions. The agar diffusion assay revealed that the oxyR mutant had increased sensitivity to H₂O₂. The transcript levels of oxidative stress defense genes, sod, ahpC, and trx, were lower in the oxyR mutant than in the wild-type strain. The turbidity of C. ochracea, simultaneously co-cultured with Streptococcus gordonii, was lower than that observed under conditions of homotypic growth. Moreover, the percentage decrease in growth of the oxyR mutant was significantly higher than that of the wild-type.

CONCLUSIONS

These results show that OxyR in C. ochracea regulates adequate in vitro growth and escapes oxidative stress.

Effects of the Quinone Oxidoreductase WrbA on Escherichia coli Biofilm Formation and Oxidative Stress

The effects of natural compounds on biofilm formation have been extensively studied, with the goal of identifying biofilm formation antagonists at sub-lethal concentrations. Salicylic and cinnamic acids are some examples of these compounds that interact with the quinone oxidoreductase WrbA, a potential biofilm modulator and an antibiofilm compound biomarker. However, WrbA’s role in biofilm development is still poorly understood. To investigate the key roles of WrbA in biofilm maturation and oxidative stress, Escherichia coli wild-type and ∆wrbA mutant strains were used. Furthermore, we reported the functional validation of WrbA as a molecular target of salicylic and cinnamic acids. The lack of WrbA did not impair planktonic growth, but rather affected the biofilm formation through a mechanism that depends on reactive oxygen species (ROS). The loss of WrbA function resulted in an ROS-sensitive phenotype that showed reductions in biofilm-dwelling cells, biofilm thickness, matrix polysaccharide content, and H₂O₂ tolerance. Endogenous oxidative events in the mutant strain generated a stressful condition to which the bacterium responded by increasing the catalase activity to compensate for the lack of WrbA. Cinnamic and salicylic acids inhibited the quinone oxidoreductase activity of purified recombinant WrbA. The effects of these antibiofilm molecules on WrbA function was proven for the first time.

The phosphotransferase system gene ptsH plays an important role in MnSOD production, biofilm formation, swarming motility, and root colonization in Bacillus cereus 905

The rhizosphere bacterium Bacillus cereus 905 is capable of promoting plant growth through effective colonization on plant roots. The sodA2-encoding manganese-containing superoxide dismutase (MnSOD2) is important for survival of B. cereus 905 in the wheat rhizosphere. However, the genes involved in regulating sodA2 expression and the mechanisms of rhizosphere colonization of B. cereus 905 are not well elucidated. In this study, we found that the deletion of the ptsH gene, which encodes the histidine-phosphorylatable protein (HPr), a component of the phosphotransferase system (PTS), causes a decrease of about 60% in the MnSOD2 expression. Evidences indicate that the ptsH dramatically influences resistance to oxidative stress, glucose uptake, as well as biofilm formation and swarming motility of B. cereus 905. Root colonization assay demonstrated that ΔptsH is defective in colonizing wheat roots, while complementation of the sodA2 gene could partially restore the ability in utilization of arabinose, a non-PTS sugar, and root colonization caused by the loss of the ptsH gene. In toto, based on the current findings, we propose that PtsH contributes to root colonization of B. cereus 905 through multiple indistinct mechanisms, involving PTS and uptake of PTS-sugars, up-regulation of MnSOD2 production, and promotion of biofilm formation and swarming motility.

Expression patterns of oxyR induced by oxidative stress from Porphyromonas gingivalis in response to photo-activated disinfection

Introduction

Porphyromonas gingivalis, an important endodontic pathogen, may be exposed to sublethal doses of photo-activated disinfection (sPAD) during root canal therapy. Such an exposure can affect bacterial survival and virulence features. In this study, we evaluated the effect of sPAD-related oxidative stresses on the expression of oxidative stress response gene (oxyR) in P. gingivalis clinical isolates surviving in vitro photodynamic treatment.

Materials and methods

To determine the sPAD, 16 clinical P. gingivalis isolates photosensitized with toluidine blue O (TBO), methylene blue (MB), and indocyanine green (ICG) were irradiated with specific wavelength and energy density of diode laser corresponding to the photosensitizers following bacterial viability measurements. The effects of sPAD on the expression ratio of oxyR of 16 clinical P. gingivalis isolates were then assessed using quantitative real-time PCR (qRT-PCR) assay.

Results

Maximum values of sPAD against P. gingivalis were 6.25, 15.6, and 25 μg/mL at fluencies of 171.87, 15.6, and 93.75 J/cm², respectively, for TBO-, ICG-, and MB-sPAD (P>0.05). ICG-, MB-, and TBO-sPAD could increase the oxyR gene expression of the clinical P. gingivalis isolates 12.3-, 5.6-, and 8.5-fold, respectively. ICG-sPAD increased the expression of oxyR gene in clinical isolates of P. gingivalis ~1.5- and 2-fold higher than TBO- and MB-sPAD, respectively.

Conclusion

Our results showed that upregulation of oxyR during sPAD may lead to better survival and increased pathogenicity of P. gingivalis isolates. Therefore, selection of appropriate photo-activated disinfection dosage should be considered for the successful treatment of endodontic infection.

The phosphotransferase system gene ptsI in Bacillus cereus regulates expression of sodA2 and contributes to colonization of wheat roots

Plant growth-promoting rhizobacteria effectively enhance plant growth and root colonization by the bacteria is a prerequisite during the process. Bacillus cereus 905, a rhizosphere bacterium originally isolated from wheat roots, colonizes the wheat rhizosphere with a large population size. We previously showed that a manganese-containing superoxide dismutase (MnSOD2), encoded by the sodA2 gene, plays an important role in colonization of the wheat rhizosphere by B. cereus 905. In this study, we identified a gene, ptsI, which positively regulates transcription of sodA2. ptsI encodes Enzyme I of the phosphotransferase system (PTS), a major regulator of carbohydrate uptake in bacteria. Assays of β-galactosidase activity and real-time quantitative PCR showed that loss of ptsI caused a 70% reduction in sodA2 expression. The ΔptsI mutant also showed a 1000-fold reduction in colonization of wheat roots, as well as a reduced growth rate in minimal media with either glucose or succinate as the sole carbon source. Artificial induction of sodA2 in the ΔptsI mutant partially restored root colonizing ability and utilization of succinate, but not glucose. These results suggest that the PTS plays an important role in rhizosphere colonization by both promoting nutrient utilization and regulating sodA2 expression in B. cereus 905.

Identification of Streptococcus cristatus peptides that repress expression of virulence genes in Porphyromonas gingivalis

Dental plaque is a complex multispecies biofilm, and is a direct precursor of periodontal disease. The virulence of periodontal pathogens, such as Porphyromonas gingivalis, is expressed in the context of this polymicrobial community. Previously, we reported an antagonistic relationship between Streptococcus cristatus and P. gingivalis, and identified arginine deiminase (ArcA) of S. cristatus as the signaling molecule to which P. gingivalis responds by repressing the expression and production of FimA protein. Here we demonstrate that direct interaction between P. gingivalis and S. cristatus is necessary for the cell-cell communication. Two surface proteins of P. gingivalis, PGN_0294 and PGN_0806, were found to interact with S. cristatus ArcA. Using a peptide array analysis, we identified several P. gingivalis-binding sites of ArcA, which led to the discovery of an 11-mer peptide with the native sequence of ArcA that repressed expression of fimbriae and of gingipains. These data indicate that a functional motif of ArcA is sufficient to selectively alter virulence gene expression in P. gingivalis, and PGN_0294 and PGN_0806 may serve as receptors for ArcA. Our findings provide a molecular basis for future rational design of agents that interfere with the initiation and formation of a P. gingivalis-induced pathogenic community.

Protein Analysis of Sapienic Acid-Treated Porphyromonas gingivalis Suggests Differential Regulation of Multiple Metabolic Pathways

Lipids endogenous to skin and mucosal surfaces exhibit potent antimicrobial activity against Porphyromonas gingivalis, an important colonizer of the oral cavity implicated in periodontitis. Our previous work demonstrated the antimicrobial activity of the fatty acid sapienic acid (C(16:1Δ6)) against P. gingivalis and found that sapienic acid treatment alters both protein and lipid composition from those in controls. In this study, we further examined whole-cell protein differences between sapienic acid-treated bacteria and untreated controls, and we utilized open-source functional association and annotation programs to explore potential mechanisms for the antimicrobial activity of sapienic acid. Our analyses indicated that sapienic acid treatment induces a unique stress response in P. gingivalis resulting in differential expression of proteins involved in a variety of metabolic pathways. This network of differentially regulated proteins was enriched in protein-protein interactions (P = 2.98 × 10(-8)), including six KEGG pathways (P value ranges, 2.30 × 10(-5) to 0.05) and four Gene Ontology (GO) molecular functions (P value ranges, 0.02 to 0.04), with multiple suggestive enriched relationships in KEGG pathways and GO molecular functions. Upregulated metabolic pathways suggest increases in energy production, lipid metabolism, iron acquisition and processing, and respiration. Combined with a suggested preferential metabolism of serine, which is necessary for fatty acid biosynthesis, these data support our previous findings that the site of sapienic acid antimicrobial activity is likely at the bacterial membrane.

IMPORTANCE

P. gingivalis is an important opportunistic pathogen implicated in periodontitis. Affecting nearly 50% of the population, periodontitis is treatable, but the resulting damage is irreversible and eventually progresses to tooth loss. There is a great need for natural products that can be used to treat and/or prevent the overgrowth of periodontal pathogens and increase oral health. Sapienic acid is endogenous to the oral cavity and is a potent antimicrobial agent, suggesting a potential therapeutic or prophylactic use for this fatty acid. This study examines the effects of sapienic acid treatment on P. gingivalis and highlights the membrane as the likely site of antimicrobial activity.

Oxidative stress enhances the expression of sulfur assimilation genes: preliminary insights on the Enterococcus faecalis iron-sulfur cluster machinery regulation

The Firmicutes bacteria participate extensively in virulence and pathological processes. Enterococcus faecalis is a commensal microorganism; however, it is also a pathogenic bacterium mainly associated with nosocomial infections in immunocompromised patients. Iron-sulfur [Fe-S] clusters are inorganic prosthetic groups involved in diverse biological processes, whose in vivo formation requires several specific protein machineries. Escherichia coli is one of the most frequently studied microorganisms regarding [Fe-S] cluster biogenesis and encodes the iron-sulfur cluster and sulfur assimilation systems. In Firmicutes species, a unique operon composed of the sufCDSUB genes is responsible for [Fe-S] cluster biogenesis. The aim of this study was to investigate the potential of the E. faecalis sufCDSUB system in the [Fe-S] cluster assembly using oxidative stress and iron depletion as adverse growth conditions. Quantitative real-time polymerase chain reaction demonstrated, for the first time, that Gram-positive bacteria possess an OxyR component responsive to oxidative stress conditions, as fully described for E. coli models. Likewise, strong expression of the sufCDSUB genes was observed in low concentrations of hydrogen peroxide, indicating that the lowest concentration of oxygen free radicals inside cells, known to be highly damaging to [Fe-S] clusters, is sufficient to trigger the transcriptional machinery for prompt replacement of [Fe-S] clusters.

Identification of a diguanylate cyclase and its role in Porphyromonas gingivalis virulence

Porphyromonas gingivalis is a Gram-negative obligate anaerobic bacterium and is considered a keystone pathogen in the initiation of periodontitis, one of the most widespread infectious diseases. Bacterial bis-(3'-5') cyclic GMP (cyclic di-GMP [c-di-GMP]) serves as a second messenger and is involved in modulating virulence factors in numerous bacteria. However, the role of this second messenger has not been investigated in P. gingivalis, mainly due to a lack of an annotation regarding diguanylate cyclases (DGCs) in this bacterium. Using bioinformatics tools, we found a protein, PGN_1932, containing a GGDEF domain. A deletion mutation in the pgn_1932 gene had a significant effect on the intracellular c-di-GMP level in P. gingivalis. Genetic analysis showed that expression of the fimA and rgpA genes, encoding the major protein subunit of fimbriae and an arginine-specific proteinase, respectively, was downregulated in the pgn_1932 mutant. Correspondingly, FimA protein production and the fimbrial display on the mutant were significantly reduced. Mutations in the pgn_1932 gene also had a significant impact on the adhesive and invasive capabilities of P. gingivalis, which are required for its pathogenicity. These findings provide evidence that the PGN_1932 protein is both responsible for synthesizing c-di-GMP and involved in biofilm formation and host cell invasion by P. gingivalis by controlling the expression and biosynthesis of FimA.

Structures of the Porphyromonas gingivalis OxyR regulatory domain explain differences in expression of the OxyR regulon in Escherichia coli and P. gingivalis

OxyR transcriptionally regulates Escherichia coli oxidative stress response genes through a reversibly reducible cysteine disulfide biosensor of cellular redox status. Structural changes induced by redox changes in these cysteines are conformationally transmitted to the dimer subunit interfaces, which alters dimer and tetramer interactions with DNA. In contrast to E. coli OxyR regulatory-domain structures, crystal structures of Porphyromonas gingivalis OxyR regulatory domains show minimal differences in dimer configuration on changes in cysteine disulfide redox status. This locked configuration of the P. gingivalis OxyR regulatory-domain dimer closely resembles the oxidized (activating) form of the E. coli OxyR regulatory-domain dimer. It correlates with the observed constitutive activation of some oxidative stress genes in P. gingivalis and is attributable to a single amino-acid insertion in P. gingivalis OxyR relative to E. coli OxyR. Modelling of full-length P. gingivalis, E. coli and Neisseria meningitidis OxyR-DNA complexes predicts different modes of DNA binding for the reduced and oxidized forms of each.

Antimicrobial strategies centered around reactive oxygen species--bactericidal antibiotics, photodynamic therapy, and beyond

Reactive oxygen species (ROS) can attack a diverse range of targets to exert antimicrobial activity, which accounts for their versatility in mediating host defense against a broad range of pathogens. Most ROS are formed by the partial reduction in molecular oxygen. Four major ROS are recognized comprising superoxide (O2•-), hydrogen peroxide (H2O2), hydroxyl radical (•OH), and singlet oxygen ((1)O2), but they display very different kinetics and levels of activity. The effects of O2•- and H2O2 are less acute than those of •OH and (1)O2, because the former are much less reactive and can be detoxified by endogenous antioxidants (both enzymatic and nonenzymatic) that are induced by oxidative stress. In contrast, no enzyme can detoxify •OH or (1)O2, making them extremely toxic and acutely lethal. The present review will highlight the various methods of ROS formation and their mechanism of action. Antioxidant defenses against ROS in microbial cells and the use of ROS by antimicrobial host defense systems are covered. Antimicrobial approaches primarily utilizing ROS comprise both bactericidal antibiotics and nonpharmacological methods such as photodynamic therapy, titanium dioxide photocatalysis, cold plasma, and medicinal honey. A brief final section covers reactive nitrogen species and related therapeutics, such as acidified nitrite and nitric oxide-releasing nanoparticles.

OxyR activation in Porphyromonas gingivalis in response to a hemin-limited environment

Porphyromonas gingivalis is a Gram-negative obligately anaerobic bacterium associated with several forms of periodontal disease, most closely with chronic periodontitis. Previous studies demonstrated that OxyR plays an important role in the aerotolerance of P. gingivalis by upregulating the expression of oxidative-stress genes. Increases in oxygen tension and in H(2)O(2) both induce activation of OxyR. It is also known that P. gingivalis requires hemin as an iron source for its growth. In this study, we found that a hemin-limited growth environment significantly enhanced OxyR activity in P. gingivalis. As a result, expression of sod, dps, and ahpC was also upregulated. Using a chromatin immunoprecipitation quantitative PCR (qPCR) analysis, DNA binding of activated OxyR to the promoter of the sod gene was enhanced in P. gingivalis grown under hemin-limited conditions compared to excess-hemin conditions. Cellular tolerance of H(2)O(2) was also enhanced when hemin was limited in the growth medium of P. gingivalis. Our work supports a model in which hemin serves as a signal for the regulation of OxyR activity and indicates that P. gingivalis coordinately regulates expression of oxidative-stress-related genes by this hemin concentration-dependent pathway.

Peroxide-sensing transcriptional regulators in bacteria

The ability to maintain intracellular concentrations of toxic reactive oxygen species (ROS) within safe limits is essential for all aerobic life forms. In bacteria, as well as other organisms, ROS are produced during the normal course of aerobic metabolism, necessitating the constitutive expression of ROS scavenging systems. However, bacteria can also experience transient high-level exposure to ROS derived either from external sources, such as the host defense response, or as a secondary effect of other seemingly unrelated environmental stresses. Consequently, transcriptional regulators have evolved to sense the levels of ROS and coordinate the appropriate oxidative stress response. Three well-studied examples of these are the peroxide responsive regulators OxyR, PerR, and OhrR. OxyR and PerR are sensors of primarily H(2)O(2), while OhrR senses organic peroxide (ROOH) and sodium hypochlorite (NaOCl). OxyR and OhrR sense oxidants by means of the reversible oxidation of specific cysteine residues. In contrast, PerR senses H(2)O(2) via the Fe-catalyzed oxidation of histidine residues. These transcription regulators also influence complex biological phenomena, such as biofilm formation, the evasion of host immune responses, and antibiotic resistance via the direct regulation of specific proteins.

Oxidative stress resistance in Porphyromonas gingivalis

Porphyromonas gingivalis, a black-pigmented, Gram-negative anaerobe, is an important etiologic agent of periodontal disease. The harsh inflammatory condition of the periodontal pocket implies that this organism has properties that will facilitate its ability to respond and adapt to oxidative stress. Because the stress response in the pathogen is a major determinant of its virulence, a comprehensive understanding of its oxidative stress resistance strategy is vital. We discuss multiple mechanisms and systems that clearly work in synergy to defend and protect P. gingivalis against oxidative damage caused by reactive oxygen species. The involvement of multiple hypothetical proteins and/or proteins of unknown function in this process may imply other unique mechanisms and potential therapeutic targets.

Role of the Porphyromonas gingivalis extracytoplasmic function sigma factor, SigH

Little is known about the regulatory mechanisms that allow Porphyromonas gingivalis to survive in the oral cavity. Here we characterize the sigma (σ) factor SigH, one of six extracytoplasmic function (ECF) σ factors encoded in the P. gingivalis genome. Our results indicate that sigH expression is upregulated by exposure to molecular oxygen, suggesting that sigH plays a role in adaptation of P. gingivalis to oxygen. Furthermore, several genes involved in oxidative stress protection, such as sod, trx, tpx, ftn, feoB2 and the hemin uptake hmu locus, are downregulated in a mutant deficient in SigH designated as V2948. ECF σ consensus sequences were identified upstream of the transcriptional start sites of these genes, consistent with the SigH-dependent regulation of these genes. Growth of V2948 was inhibited in the presence of 6% oxygen when compared with the wild-type W83 strain, whereas in anaerobic conditions both strains were able to grow. In addition, reduced growth of V2948 was observed in the presence of peroxide and the thiol-oxidizing reagent diamide when compared with the W83 strain. The SigH-deficient strain V2948 also exhibited reduced hemin uptake, consistent with the observed reduced expression of genes involved in hemin uptake. Finally, survival of V2948 was reduced in the presence of host cells compared with the wild-type W83 strain. Collectively, our studies demonstrate that SigH is a positive regulator of gene expression required for survival of the bacterium in the presence of oxygen and oxidative stress, hemin uptake and virulence.

Effects of chronic sub-lethal oxidative stress on biofilm formation by Azotobacter vinelandii

This work showed that perturbations of the physiological steady-state level of reactive oxygen species (ROS) affected biofilm genesis and the characteristics of the model bacterium Azotobacter vinelandii. To get a continuous endogenous source of ROS, a strain exposed to chronic sub-lethal oxidative stress was deprived of the gene coding for the antioxidant rhodanese-like protein RhdA (MV474). In this study MV474 biofilm showed (i) a seven-fold higher growth rate, (ii) induction of catalase and alkyl-hydroxyl-peroxidase enzymes, (iii) higher average thicknesses due to increased production of a polysaccharide-rich extracellular matrix and (iv) less susceptibility to hydrogen peroxide than the wild-type strain (UW136). MV474 showed increased swimming and swarming activity and the swarming colonies experienced a higher level of oxidative stress compared to UW136. A continuous exogenous source of ROS increased biofilm formation in UW136. Overall, chronic sub-lethal oxidative events promoted sessile behavior in A. vinelandii.

Differential expression and adherence of Porphyromonas gingivalis FimA genotypes

Porphyromonas gingivalis is a primary pathogen involved in the initiation and progression of adult chronic periodontitis. Its colonization on oral surfaces is a necessary first step leading to infection. FimA, a subunit protein of major (long) fimbriae, is a well-known virulence factor. Based on its nucleotide sequence, FimA is classified into several genotypes. We compared here the transcriptional levels of the fimA gene in several P. gingivalis strains using real-time polymerase chain reaction analysis, fimbrial display on the P. gingivalis surface using transmission electronic microscopy, and the adherence competencies of P. gingivalis strains carrying different types of FimAs towards saliva and Streptococcus gordonii surfaces using mutagenesis analysis. We demonstrated differential expression of each fimA gene in these P. gingivalis strains. A correlation of the transcription level of fimA and binding activity of P. gingivalis was revealed. We show that P. gingivalis strains with genotype I and II of FimA are efficient in interaction with saliva or S. gordonii. This work highlights the important role of FimA type I and II in P. gingivalis attachment to oral surfaces.

Porphyromonas gingivalis-dendritic cell interactions: consequences for coronary artery disease

An estimated 80 million US adults have one or more types of cardiovascular diseases. Atherosclerosis is the single most important contributor to cardiovascular diseases; however, only 50% of atherosclerosis patients have currently identified risk factors. Chronic periodontitis, a common inflammatory disease, is linked to an increased cardiovascular risk. Dendritic cells (DCs) are potent antigen presenting cells that infiltrate arterial walls and may destabilize atherosclerotic plaques in cardiovascular disease. While the source of these DCs in atherosclerotic plaques is presently unclear, we propose that dermal DCs from peripheral inflamed sites such as CP tissues are a potential source. This review will examine the role of the opportunistic oral pathogen Porphyromonas gingivalis in invading DCs and stimulating their mobilization and misdirection through the bloodstream. Based on our published observations, combined with some new data, as well as a focused review of the literature we will propose a model for how P. gingivalis may exploit DCs to gain access to systemic circulation and contribute to coronary artery disease. Our published evidence supports a significant role for P. gingivalis in subverting normal DC function, promoting a semimature, highly migratory, and immunosuppressive DC phenotype that contributes to the inflammatory development of atherosclerosis and, eventually, plaque rupture.

oxyR, a LysR-type regulator involved in Klebsiella pneumoniae mucosal and abiotic colonization

Colonization of the gastrointestinal tract is the first event in Klebsiella pneumoniae nosocomial infections, followed by colonization of the bladder or respiratory tract or entry into the bloodstream. To survive in the host, bacteria must harbor specific traits and overcome multiple stresses. OxyR is a conserved bacterial transcription factor with a key role both in the upregulation of defense mechanisms against oxidative stress and in pathogenesis by enhancing biofilm formation, fimbrial expression, and mucosal colonization. A homolog of oxyR was detected in silico in the K. pneumoniae sequenced genome and amplified from the LM21 wild-type strain. To determine the role of oxyR in K. pneumoniae host-interaction processes, an oxyR isogenic mutant was constructed, and its behavior was assessed. At concentrations lower than 10(7) ml(-1), oxyR-deficient organisms were easily killed by micromolar concentrations of H(2)O(2) and exhibited typical aerobic phenotypes. The oxyR mutant was impaired in biofilm formation and types 1 and 3 fimbrial gene expression. In addition, the oxyR mutant was unable to colonize the murine gastrointestinal tract, and in vitro assays showed that it was defective in adhesion to Int-407 and HT-29 intestinal epithelial cells. The behavior of the oxyR mutant was also determined under hostile conditions, reproducing stresses encountered in the gastrointestinal environment: deletion of oxyR resulted in higher sensitivity to bile and acid stresses but not to osmotic stress. These results show the pleiotropic role of oxyR in K. pneumoniae gastrointestinal colonization.

The OxyR homologue in Tannerella forsythia regulates expression of oxidative stress responses and biofilm formation

Tannerella forsythia is an anaerobic periodontal pathogen that encounters constant oxidative stress in the human oral cavity due to exposure to air and reactive oxidative species from coexisting dental plaque bacteria as well as leukocytes. In this study, we sought to characterize a T. forsythia ORF with close similarity to bacterial oxidative stress response sensor protein OxyR. To analyse the role of this OxyR homologue, a gene deletion mutant was constructed and characterized. Aerotolerance, survival after hydrogen peroxide challenge and transcription levels of known bacterial antioxidant genes were then determined. Since an association between oxidative stress and biofilm formation has been observed in bacterial systems, we also investigated the role of the OxyR protein in biofilm development by T. forsythia. Our results showed that aerotolerance, sensitivity to peroxide challenge and the expression of oxidative stress response genes were significantly reduced in the mutant as compared with the wild-type strain. Moreover, the results of biofilm analyses showed that, as compared with the wild-type strain, the oxyR mutant showed significantly less autoaggregation and a reduced ability to form mixed biofilms with Fusobacterium nucleatum. In conclusion, a gene annotated in the T. forsythia genome as an oxyR homologue was characterized. Our studies showed that the oxyR homologue in T. forsythia constitutively activates antioxidant genes involved in resistance to peroxides as well as oxygen stress (aerotolerance). In addition, the oxyR deletion attenuates biofilm formation in T. forsythia.

Regulation of hemin binding proteins by a novel transcriptional activator in Porphyromonas gingivalis

One of the features of the periodontal pathogen Porphyromonas gingivalis is the presence of complex iron acquisition systems that include an hmuYRSTUV locus. HmuY and HmuR are hemin binding proteins required for P. gingivalis growth. Previous studies have demonstrated that expression of the hmu locus is regulated in response to environmental changes, such as growth phases. However, the mechanisms involved in hmu gene regulation are poorly understood. Here we report that a novel transcriptional activator, PG1237, is required for the expression of humY and humR, but not other iron acquisition-related genes, such as fetB and tlr, which also encode hemin binding proteins. Real-time reverse transcription-PCR analysis revealed that a mutation in the pg1237 gene decreased expression of hmuY and hmuR 149- and 25-fold, respectively, compared to that observed in the wild-type strain. In addition, differential expression of hmuY, hmuR, and the pg1237 gene was found to be quorum-sensing dependent, such that higher expression levels of these genes were observed when P. gingivalis was grown at a lower cell density, such as that seen during the early exponential growth phase. This work demonstrates the involvement of a novel transcriptional activator, PG1237, in expression of the hmu operon in a cell density-dependent fashion.