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

Photodynamic disruption of a polymicrobial biofilm of two periodontal species using indocyanine green-loaded nanospheres

OBJECTIVE

Antimicrobial photodynamic therapy (aPDT) is considered a potential treatment for biofilm infections, which have become an increasing health issue because of the rise in antimicrobial resistance. This study aimed to evaluate the bactericidal effect of aPDT using indocyanine green-loaded nanospheres with chitosan coating (ICG-Nano/c) against polymicrobial periodontal biofilms.

METHODS

Composite biofilms of Porphyromonas gingivalis and Streptococcus gordonii were constructed in 96-well plates, and aPDT with ICG-Nano/c and an 810 nm diode laser was performed either by direct irradiation or transmitting irradiation through a 3-mm-thick gingival model. The efficacy of ICG-Nano/c-based aPDT was compared with antibiotics (minocycline and amoxicillin). Additionally, attenuated aPDT under sublethal conditions was used to investigate gene expression related to the antioxidant response (oxyR and sod of P. gingivalis) and biofilm formation via quorum sensing (luxS of both species) with real-time polymerase chain reaction.

RESULTS

ICG-Nano/c-based aPDT significantly reduced the bacterial load in the biofilm, achieving at least a 2 log10 reduction in colony-forming units within 5 min for both irradiation methods. After 6 h of treatment, the bactericidal effects of aPDT and antibiotics were similar, but after 32 h, antibiotics were more effective, particularly against P. gingivalis. Attenuated aPDT showed a slight increase in sod expression in P. gingivalis, while luxS expression decreased in both bacteria.

CONCLUSION

The ICG-Nano/c-based aPDT system exerted a certain degree of bactericidal activity against a composite biofilm of periodontal bacteria. Therefore, it has potential as an alternative option or adjunctive therapy to conventional antibiotics in periodontal treatment.

Growth of Porphyromonas gingivalis on human serum albumin triggers programmed cell death

Aims

Gingival crevicular fluid (GCF) constitutes the primary growth substrate for Porphyromonas gingivalis in vivo. The goal of this work was to evaluate the growth of different strains of P. gingivalis on human serum albumin (HSA), a major constituent of GCF.

Methods

Growth of five different strains of P. gingivalis in the HSA medium was examined and, surprisingly, three of the strains underwent autolysis within 24 h. Comparative transcriptomic analysis was used to identify genes involved in autolysis.

Results

Two highly related reference strains (W50 and W83) differed dramatically in their survival when grown on HSA. Strain W83 grew fast and lysed within 24 h, while W50 survived for an additional 20 h. Differential gene expression analysis led us to a gene cluster containing enzymes involved in arginine metabolism and a gene predicted to be lytic murein transglycosylase, which are known to play a role in autolysis. Deletion of this gene (PG0139) resulted in a mutant that did not lyse, and complementation restored the HSA lysis phenotype, indicating that this enzyme plays a central role in the autolysis of P. gingivalis.

Conclusions

P. gingivalis undergoes autolysis when provided with HSA as a substrate for growth.

DNA-aptamer-nanographene oxide as a targeted bio-theragnostic system in antimicrobial photodynamic therapy against Porphyromonas gingivalis

The aim of this study was to design and evaluate the specificity of a targeted bio-theragnostic system based on DNA-aptamer-nanographene oxide (NGO) against Porphyromonas gingivalis during antimicrobial photodynamic therapy (aPDT). Following synthesis and confirmation of NGO, the binding of selected labeled DNA-aptamer to NGO was performed and its hemolytic activity, cytotoxic effect, and release times were evaluated. The specificity of DNA-aptamer-NGO to P. gingivalis was determined. The antimicrobial effect, anti-biofilm potency, and anti-metabolic activity of aPDT were then assessed after the determination of the bacteriostatic and bactericidal concentrations of DNA-aptamer-NGO against P. gingivalis. Eventually, the apoptotic effect and anti-virulence capacity of aPDT based on DNA-aptamer-NGO were investigated. The results showed that NGO with a flaky, scale-like, and layered structure in non-cytotoxic DNA-aptamer-NGO has a continuous release in the weak-acid environment within a period of 240 h. The binding specificity of DNA-aptamer-NGO to P. gingivalis was confirmed by flow cytometry. When irradiated, non-hemolytic DNA-aptamer-NGO were photoactivated, generated ROS, and led to a significant decrease in the cell viability of P. gingivalis (P < 0.05). Also, the data indicated that DNA-aptamer-NGO-mediated aPDT led to a remarkable reduction of biofilms and metabolic activity of P. gingivalis compared to the control group (P < 0.05). In addition, the number of apoptotic cells increased slightly (P > 0.05) and the expression level of genes involved in bacterial biofilm formation and response to oxidative stress changed significantly after exposure to aPDT. It is concluded that aPDT using DNA-aptamer-NGO as a targeted bio-theragnostic system is a promising approach to detect and eliminate P. gingivalis as one of the main bacteria involved in periodontitis in periopathogenic complex in real-time and in situ.

Comparisons of the killing effect of direct current partially mediated by reactive oxygen species on Porphyromonas gingivalis and Prevotella intermedia in planktonic state and biofilm state - an in vitro study

Background/purpose

Bacterial biofilms formed on the surface of tissues and biomaterials are major causes of chronic infections in humans. Among them, Porphyromonas gingivalis (P. gingivalis) and Prevotella intermedia (P. intermedia) are anaerobic pathogens causing dental infections associated with periodontitis. In this study, we evaluated the killing effect and underlying mechanisms of direct current (DC) as an antimicrobial method in vitro.

Materials and methods

We chose P. gingivalis and P. intermedia in different states to make comparisons of the killing effect of DC. By viable bacteria counting, fluorescent live/dead staining, reactive oxygen species (ROS) assay, addition of ROS scavenger DMTU and mRNA expression assay of ROS scavenging genes, the role of ROS in the killing effect was explored.

Results

The planktonic and biofilm states of two bacteria could be effectively killed by low-intensity DC. For the killing effect of 1000 μA DC, there were significant differences whether on planktonic P. gingivalis and P. intermedia (mean killing values: 2.40 vs 2.62 log₁₀ CFU/mL) or on biofilm state of those (mean killing values: 0.63 vs 0.98 log₁₀ CFU/mL). 1000 μA DC greatly induced ROS production and the mRNA expression of ROS scavenging genes. DMTU could partially decrease the killing values of DC and downregulate corresponding gene’s expression.

Conclusion

1000 μA DC can kill P. gingivalis and P. intermedia in two states by promoting overproduction of ROS, and P. intermedia is more sensitive to DC than P. gingivalis. These findings indicate low-intensity DC may be a promising approach in treating periodontal infections.

How Microbes Defend Themselves From Incoming Hydrogen Peroxide

Microbes rely upon iron as a cofactor for many enzymes in their central metabolic processes. The reactive oxygen species (ROS) superoxide and hydrogen peroxide react rapidly with iron, and inside cells they can generate both enzyme and DNA damage. ROS are formed in some bacterial habitats by abiotic processes. The vulnerability of bacteria to ROS is also apparently exploited by ROS-generating host defense systems and bacterial competitors. Phagocyte-derived O 2 - can toxify captured bacteria by damaging unidentified biomolecules on the cell surface; it is unclear whether phagocytic H2O2, which can penetrate into the cell interior, also plays a role in suppressing bacterial invasion. Both pathogenic and free-living microbes activate defensive strategies to defend themselves against incoming H2O2. Most bacteria sense the H2O2via OxyR or PerR transcription factors, whereas yeast uses the Grx3/Yap1 system. In general these regulators induce enzymes that reduce cytoplasmic H2O2 concentrations, decrease the intracellular iron pools, and repair the H2O2-mediated damage. However, individual organisms have tailored these transcription factors and their regulons to suit their particular environmental niches. Some bacteria even contain both OxyR and PerR, raising the question as to why they need both systems. In lab experiments these regulators can also respond to nitric oxide and disulfide stress, although it is unclear whether the responses are physiologically relevant. The next step is to extend these studies to natural environments, so that we can better understand the circumstances in which these systems act. In particular, it is important to probe the role they may play in enabling host infection by microbial pathogens.

Anti-Bacterial and Anti-Inflammatory Effects of Toothpaste with Swiss Medicinal Herbs towards Patients Suffering from Gingivitis and Initial Stage of Periodontitis: from Clinical Efficacy to Mechanisms

Objective: To distinguish clinical effects and mechanisms of sodium monofluorophosphate plus xylitol and herbal extracts of Swiss medicinal plants (Chamomilla recutita, Arnica montana, Echinacea purpurea, and Salvia officinalis). Materials and Methods: A 2-month-long comparative clinical study of toothpaste containing 1450 ppm sodium monofluorophosphate and xylitol (control, 15 patients) and toothpaste additionally containing extracts of the medicinal herbs (experiment, 35 patients) was performed on patients with gingivitis and the initial stage of periodontitis. Clinical indices of gingivitis/periodontitis were quantified by Loe & Silness’s, CPITN, OHI-S, and PMA indexes. The pro-inflammatory and anti-inflammatory interleukins, nitrites/nitrates, total antioxidant activity, and bacterial pattern characteristic for gingivitis and periodontitis were quantified in the gingival crevicular fluid and plaque. In the in vitro tests, direct anti-bacterial effects, inhibition of catalase induction in Staphylococcus aureus, in response to oxidative burst of phagocytes, and intracellular bacterial killing were determined for the toothpastes, individual plant extracts, and their mixture. Results: Experimental toothpaste was more efficient clinically and in the diminishing of bacterial load specific for gingivitis/periodontitis. Although the control toothpaste exerted a direct moderate anti-bacterial effect, herbal extracts provided anti-inflammatory, anti-oxidant, direct, and indirect anti-bacterial actions through inhibition of bacterial defence against phagocytes. Conclusions: Chemical and plant-derived anti-bacterials to treat gingivitis and periodontitis at the initial stage should be used in combination amid their different mechanisms of action. Plant-derived actives for oral care could substitute toxic chemicals due to multiple modes of positive effects.

PgRsp Is a Novel Redox-Sensing Transcription Regulator Essential for Porphyromonas gingivalis Virulence

Porphyromonas gingivalis is one of the etiological agents of chronic periodontitis. Both heme and oxidative stress impact expression of genes responsible for its survival and virulence. Previously we showed that P. gingivalis ferric uptake regulator homolog affects expression of a gene encoding a putative Crp/Fnr superfamily member, termed P. gingivalis redox-sensing protein (PgRsp). Although PgRsp binds heme and shows the highest similarity to proteins assigned to the CooA family, it could be a member of a novel, separate family of proteins with unknown function. Expression of the pgrsp gene is autoregulated and iron/heme dependent. Genes encoding proteins engaged in the oxidative stress response were upregulated in the pgrsp mutant (TO11) strain compared with the wild-type strain. The TO11 strain showed higher biomass production, biofilm formation, and coaggregation ability with Tannerella forsythia and Prevotella intermedia. We suggest that PgRsp may regulate production of virulence factors, proteases, Hmu heme acquisition system, and FimA protein. Moreover, we observed growth retardation of the TO11 strain under oxidative conditions and decreased survival ability of the mutant cells inside macrophages. We conclude that PgRsp protein may play a role in the oxidative stress response using heme as a ligand for sensing changes in redox status, thus regulating the alternative pathway of the oxidative stress response alongside OxyR.

Deletion of a conserved transcript PG_RS02100 expressed during logarithmic growth in Porphyromonas gingivalis results in hyperpigmentation and increased tolerance to oxidative stress

The oral obligate anaerobe Porphyromonas gingivalis possesses a small conserved transcript PG_RS02100 of unknown function we previously identified using small RNA-seq analysis as expressed during logarithmic growth. In this study, we sought to determine if PG_RS02100 plays a role in P. gingivalis growth or stress response. We show that a PG_RS02100 deletion mutant’s (W83Δ514) ability to grow under anaerobic conditions was no different than wildtype (W83), but it was better able to survive hydrogen peroxide exposure when cultured under heme limiting growth conditions, and was more aerotolerant when plated on enriched whole blood agar and exposed to atmospheric oxygen. Together, these results indicate that PG_RS02100 plays a role in surviving oxidative stress in actively growing P. gingivalis and that P. gingivalis’ response to exogenous hydrogen peroxide stress is linked to heme availability. Relative qRT-PCR expression analysis of oxyR, trx-1, tpx, sodB, ahpC, dinF, cydB, and frd, in W83Δ514 and W83 in response to 1 h exogenous dioxygen or hydrogen peroxide exposure, when cultured with varying heme availability, support our phenotypic evidence that W83Δ514 has a more highly primed defense system against exogenous peroxide, dioxygen, and heme generated ROS. Interestingly, W83Δ514 turned black faster than W83 when cultured on whole blood agar, suggesting it was able to accumulate heme more rapidly. The mechanism of increased heme acquisition observed in W83Δ514 is not yet known. However, it is clear that PG_RS02100 is involved in modulating the P. gingivalis cell surface in a manner related to survival, particularly against oxidative stress.

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.

Effect of extracytoplasmic function sigma factors on autoaggregation, hemagglutination, and cell surface properties of Porphyromonas gingivalis

Porphyromonas gingivalis is a bacterium frequently isolated from chronic periodontal lesions and is involved in the development of chronic periodontitis. To colonize the gingival crevice, P. gingivalis has to adapt to environmental stresses. Microbial gene expression is regulated by transcription factors such as those in two-component systems and extracytoplasmic function (ECF) sigma factors. ECF sigma factors are involved in the regulation of environmental stress response genes; however, the roles of individual ECF sigma factors are largely unknown. The purpose of this study was to investigate the functions, including autoaggregation, hemagglutination, gingipain activity, susceptibility to antimicrobial agents, and surface structure formation, of P. gingivalis ECF sigma factors encoded by SigP (PGN_0274), SigCH (PGN_0319), PGN_0450, PGN_0970, and SigH (PGN_1740). Various physiological aspects of the sigP mutant were affected; autoaggregation was significantly decreased at 60 min (p < 0.001), hemagglutination activity was markedly reduced, and enzymatic activities of Kgp and Rgps were significantly decreased (p < 0.001). The other mutants also showed approximately 50% reduction in Rgps activity. Kgp activity was significantly reduced in the sigH mutant (p < 0.001). No significant differences in susceptibilities to tetracycline and ofloxacin were observed in the mutants compared to those of the wild-type strain. However, the sigP mutant displayed an increased susceptibility to ampicillin, whereas the PGN_0450 and sigH mutants showed reduced susceptibility. Transmission electron microscopy images revealed increased levels of outer membrane vesicles formed at the cell surfaces of the sigP mutant. These results indicate that SigP is important for bacterial surface-associated activities, including gingipain activity, autoaggregation, hemagglutination, vesicle formation, and antimicrobial susceptibility.

Genes Contributing to Porphyromonas gingivalis Fitness in Abscess and Epithelial Cell Colonization Environments

Porphyromonas gingivalis is an important cause of serious periodontal diseases, and is emerging as a pathogen in several systemic conditions including some forms of cancer. Initial colonization by P. gingivalis involves interaction with gingival epithelial cells, and the organism can also access host tissues and spread haematogenously. To better understand the mechanisms underlying these properties, we utilized a highly saturated transposon insertion library of P. gingivalis, and assessed the fitness of mutants during epithelial cell colonization and survival in a murine abscess model by high-throughput sequencing (Tn-Seq). Transposon insertions in many genes previously suspected as contributing to virulence showed significant fitness defects in both screening assays. In addition, a number of genes not previously associated with P. gingivalis virulence were identified as important for fitness. We further examined fitness defects of four such genes by generating defined mutations. Genes encoding a carbamoyl phosphate synthetase, a replication-associated recombination protein, a nitrosative stress responsive HcpR transcription regulator, and RNase Z, a zinc phosphodiesterase, showed a fitness phenotype in epithelial cell colonization and in a competitive abscess infection. This study verifies the importance of several well-characterized putative virulence factors of P. gingivalis and identifies novel fitness determinants of the organism.

Periodontal status and serum biomarker levels in HFE haemochromatosis patients. A case-series study

AIM

To investigate the association between periodontal status and serum biomarkers in patients with HFE haemochromatosis.

MATERIAL AND METHODS

This clinical case series included 84 HFE-C282Y homozygous patients. Periodontal evaluation was performed using clinical attachment level, probing depth, gingival bleeding index, visible plaque index and gingival index. Serum markers of iron metabolism were collected from medical records. The relationship between serum biomarkers of iron burden and the severity of periodontitis was investigated.

RESULTS

The study population consisted of 47 men and 37 women, routinely treated in the Unit of Hepatology, University Hospital, Rennes. All patients presented with periodontitis (mild: n = 1, moderate: n = 37 and severe: n = 46). There was a positive association between transferrin saturation >45% and the severity of periodontitis (adjusted odds ratio = 5.49, p = .002).

CONCLUSION

Severe periodontitis is associated with the severity of iron burden in patients with HFE-related hereditary haemochromatosis. Dental examination should be included in the initial assessment of all these patients.

Meristem Plant Cells as a Sustainable Source of Redox Actives for Skin Rejuvenation

Recently, aggressive advertisement claimed a “magic role” for plant stem cells in human skin rejuvenation. This review aims to shed light on the scientific background suggesting feasibility of using plant cells as a basis of anti-age cosmetics. When meristem cell cultures obtained from medicinal plants are exposed to appropriate elicitors/stressors (ultraviolet, ultrasound ultraviolet (UV), ultrasonic waves, microbial/insect metabolites, heavy metals, organic toxins, nutrient deprivation, etc.), a protective/adaptive response initiates the biosynthesis of secondary metabolites. Highly bioavailable and biocompatible to human cells, low-molecular weight plant secondary metabolites share structural/functional similarities with human non-protein regulatory hormones, neurotransmitters, pigments, polyamines, amino-/fatty acids. Their redox-regulated biosynthesis triggers in turn plant cell antioxidant and detoxification molecular mechanisms resembling human cell pathways. Easily isolated in relatively large quantities from contaminant-free cell cultures, plant metabolites target skin ageing mechanisms, above all redox imbalance. Perfect modulators of cutaneous oxidative state via direct/indirect antioxidant action, free radical scavenging, UV protection, and transition-metal chelation, they are ideal candidates to restore photochemical/redox/immune/metabolic barriers, gradually deteriorating in the ageing skin. The industrial production of plant meristem cell metabolites is toxicologically and ecologically sustainable for fully “biological” anti-age cosmetics.

Effects of Standardised Fermented Papaya Gel on Clinical Symptoms, Inflammatory Cytokines, and Nitric Oxide Metabolites in Patients with Chronic Periodontitis: An Open Randomised Clinical Study

The clinical efficacy of topical administration of standardised fermented papaya gel (SFPG), known to have antioxidant and anti-inflammatory properties, versus conventional therapy was evaluated in a group of 84 patients with moderate-to-severe periodontitis, randomly assigned to control group (n = 45) undergoing traditional pharmacologic/surgical protocols or to experimental group (n = 39), additionally treated with intragingival pocket SFPG (7 g) applications (15 min daily for 10 days). Patients undergoing SFPG treatment showed significant (P < 0.05), durable improvement of three major clinical indices of disease severity: reduced bleeding (day 7), plaque and gingival conditions (day 14), and consistent gingival pocket depth reduction (day 45). Proinflammatory nitric oxide metabolites reached normal values in plasma (day 14) and gingival crevicular fluid (GCF) at day 45 with SFPG applications compared to controls that did not reach normalisation. Levels of highly increased proinflammatory (IL-1B, IL-6) and suppressed anti-inflammatory (IL-10) cytokines normalised in the SFPG group by days 14 (plasma) and 45 (GCF), but never in the control group. Although not acting directly as antibiotic, SFPG acted in synergy with human granulocytes blocking adaptive catalase induction in S. aureus in response to granulocyte-derived oxidative stress, thus enhancing intracellular bacterial killing.

Fimbriae-mediated outer membrane vesicle production and invasion of Porphyromonas gingivalis

Porphyromonas gingivalis is a keystone periopathogen that plays an essential role in the progress of periodontitis. Like other gram-negative bacteria, the ability of P. gingivalis to produce outer membrane vesicles is a strategy used to interact with, and survive within its biological niches. Here we compared the protein components associated with vesicles derived from a fimbriated strain (33277) and an afimbriated strain (W83) of P. gingivalis using proteomic analyses. Some well-known virulence factors were identified in vesicles from both strains, such as gingipains and hemagglutinin. In contrast, FimC, FimD, and FimE, minor components of long fimbriae were found exclusively in 33277 vesicles, while proteins with a tetratricopeptide repeat (TPR) domain were unique to W83 vesicles. We found that significantly more 33277 than W83 vesicles were internalized into human oral keratinocytes and gingival fibroblasts. Interestingly, FimA, a well-known adhesin responsible for the attachment and invasion of P. gingivalis into host cells, was not essential for the invasive capabilities of P. gingivalis vesicles. Rather minor components of long fimbriae were required for an efficient invasive activity of vesicles. The most striking finding was that P. gingivalis strains lacking or having a reduced FimA expression showed a significant reduction in vesiculation. These results suggest that production and pathogenicity of P. gingivalis vesicles may largely depend on expression of the fim locus, and that the integration of vesicle production and pathogenicity with fimbrial expression may allow P. gingivalis to confer upon itself certain functional advantages.

Metabolome variations in the Porphyromonas gingivalis vimA mutant during hydrogen peroxide-induced oxidative stress

The adaptability and survival of Porphyromonas gingivalis in the oxidative microenvironment of the periodontal pocket are indispensable for survival and virulence, and are modulated by multiple systems. Among the various genes involved in P. gingivalis oxidative stress resistance, vimA gene is a part of the 6.15-kb locus. To elucidate the role of a P. gingivalis vimA-defective mutant in oxidative stress resistance, we used a global approach to assess the transcriptional profile, to study the unique metabolome variations affecting survival and virulence in an environment typical of the periodontal pocket. A multilayered protection strategy against oxidative stress was noted in P. gingivalis FLL92 with upregulation of detoxifying genes. The duration of oxidative stress was shown to differentially modulate transcription with 94 (87%) genes upregulated twofold during 10 min and 55 (83.3%) in 15 min. Most of the upregulated genes (55%), fell in the hypothetical/unknown/unassigned functional class. Metabolome variation showed reduction in fumarate and formaldehyde, hence resorting to alternative energy generation and maintenance of a reduced metabolic state. There was upregulation of transposases, genes encoding for the metal ion binding protein transport and secretion system.

Iron- and hemin-dependent gene expression of Porphyromonas gingivalis

Although iron under anaerobic conditions is more accessible and highly reactive because of its reduced form, iron-dependent regulation is not well known in anaerobic bacteria. Here, we investigated iron- and hemin-dependent gene regulation in Porphyromonas gingivalis, an established periodontopathogen that primarily inhabits anaerobic pockets. Whole-genome microarrays of P. gingivalis genes were used to compare the levels of gene expression under iron-replete and iron-depleted conditions as well as under hemin-replete and hemin-depleted conditions. Under iron-depleted conditions, the expression of genes encoding proteins that participate in iron uptake and adhesion/invasion of host cells was increased, while that of genes encoding proteins involved in iron storage, energy metabolism, and electron transport was decreased. Interestingly, many of the genes with altered expression had no known function. Limiting the amount of hemin also resulted in a reduced expression of the genes encoding proteins involved in energy metabolism and electron transport. However, hemin also had a significant effect on many other biological processes such as oxidative stress protection and lipopolysaccharide synthesis. Overall, comparison of the data from iron-depleted conditions to those from hemin-depleted ones showed that although some regulation is through the iron derived from hemin, there also is significant distinct regulation through hemin only. Furthermore, our data showed that the molecular mechanisms of iron-dependent regulation are novel as the deletion of the putative Fur protein had no effect on the expression of iron-regulated genes. Finally, our functional studies demonstrated greater survivability of host cells in the presence of the iron-stressed bacterium than the iron-replete P. gingivalis cells. The major iron-regulated proteins encoded by PG1019-20 may play a role in this process as deletion of these sequences also resulted in reduced survival of the bacterium when grown with eukaryotic cells. Taken together, the results of this study demonstrated the utility of whole-genome microarray analysis for the identification of genes with altered expression profiles during varying growth conditions and provided a framework for the detailed analysis of the molecular mechanisms of iron and hemin acquisition, metabolism and virulence of P. gingivalis.

Microarray analysis of the transcriptional responses of Porphyromonas gingivalis to polyphosphate

BACKGROUND

Polyphosphate (polyP) has bactericidal activity against a gram-negative periodontopathogen Porphyromonas gingivalis, a black-pigmented gram-negative anaerobic rod. However, current knowledge about the mode of action of polyP against P. gingivalis is incomplete. To elucidate the mechanisms of antibacterial action of polyP against P. gingivalis, we performed the full-genome gene expression microarrays, and gene ontology (GO) and protein-protein interaction network analysis of differentially expressed genes (DEGs).

RESULTS

We successfully identified 349 up-regulated genes and 357 down-regulated genes (>1.5-fold, P < 0.05) in P. gingivalis W83 treated with polyP75 (sodium polyphosphate, Na(n+2)P(n)O3(n+1); n = 75). Real-time PCR confirmed the up- and down-regulation of some selected genes. GO analysis of the DEGs identified distinct biological themes. Using 202 DEGs belonging to the biological themes, we generated the protein-protein interaction network based on a database of known and predicted protein interactions. The network analysis identified biological meaningful clusters related to hemin acquisition, energy metabolism, cell envelope and cell division, ribosomal proteins, and transposon function.

CONCLUSIONS

polyP probably exerts its antibacterial effect through inhibition of hemin acquisition by the bacterium, resulting in severe perturbation of energy metabolism, cell envelope biosynthesis and cell division, and elevated transposition. Further studies will be needed to elucidate the exact mechanism by which polyP induces up-regulation of the genes related to ribosomal proteins. Our results will shed new light on the study of the antibacterial mechanism of polyP against other related bacteria belonging to the black-pigmented Bacteroides species.