Porphyromonas gingivalis htrA is involved in cellular invasion and in vivo survival

Proteolytic activity of surface-exposed HtrA determines its expression level and is needed to survive acidic conditions in Clostridioides difficile

To survive in the host, pathogenic bacteria need to be able to react to the unfavorable conditions that they encounter, like low pH, elevated temperatures, antimicrobial peptides and many more. These conditions may lead to unfolding of envelope proteins and this may be lethal. One of the mechanisms through which bacteria are able to survive these conditions is through the protease/foldase activity of the high temperature requirement A (HtrA) protein. The gut pathogen Clostridioides difficile encodes one HtrA homolog that is predicted to contain a membrane anchor and a single PDZ domain. The function of HtrA in C. difficile is hitherto unknown but previous work has shown that an insertional mutant of htrA displayed elevated toxin levels, less sporulation and decreased binding to target cells. Here, we show that HtrA is membrane associated and localized on the surface of C. difficile and characterize the requirements for proteolytic activity of recombinant soluble HtrA. In addition, we show that the level of HtrA in the bacteria heavily depends on its proteolytic activity. Finally, we show that proteolytic activity of HtrA is required for survival under acidic conditions.

Delineation of global, absolutely essential and conditionally essential pangenomes of Porphyromonas gingivalis

Porphyromonas gingivalis is a Gram-negative, anaerobic oral pathobiont, an etiological agent of periodontitis and the most commonly studied periodontal bacterium. Multiple low passage clinical isolates were sequenced, and their genomes compared to several laboratory strains. Phylogenetic distances were mapped, a gene absence-presence matrix generated, and core (present in all genomes) and accessory (absent in one or more genomes) genes delineated. Subsequently, a second pangenome delineating the prevalence of inherently essential genes was generated. The prevalence of genes conditionally essential for surviving tobacco exposure, abscess formation and epithelial invasion was also determined, in addition to genes encoding key proteolytic enzymes containing putative signal peptides. While the absolutely essential pangenome was highly conserved, significant differences in the complete and conditionally essential pangenomes were apparent. Thus, genetic plasticity appears to lie primarily in gene sets facilitating adaptation to variant disease-related environments. Those genes that are highly pervasive in the P. gingivalis absolutely essential pangenome or are highly prevalent and essential for fitness in disease-relevant models, may represent particularly attractive therapeutic targets worthy of further investigation. As mutations in absolutely essential genes are expected to be lethal, the data provided herein should also facilitate improved planning for P. gingivalis gene mutation strategies.

Investigating the role of a Tannerella forsythia HtrA protease in host protein degradation and inflammatory response

INTRODUCTION

Degradation of host proteins by bacterial proteases leads to the subversion of the host response and disruption of oral epithelial integrity, which is considered an essential factor in the progression of periodontitis. High-temperature requirement A (HtrA) protease, which is critical for bacterial survival and environmental adaptation, is found in several oral bacteria, including the periodontal pathogen Tannerella forsythia. This study investigated the proteolytic activity of HtrA from T. forsythia and its ability to modulate the host response.

METHODS

HtrA of T. forsythia was identified bioinformatically and produced as a recombinant protein. T. forsythia mutants with depleted and restored HtrA production were constructed. The effect of T. forsythia wild-type, mutants and recombinant HtrA on the degradation of casein and E-cadherin was tested in vitro. Additionally, the responses of human gingival fibroblasts and U937 macrophages to the different HtrA-stimuli were investigated and compared to those triggered by the HtrA-deficient mutant.

RESULTS

T. forsythia wild-type producing HtrA as well as the recombinant enzyme exhibited proteolytic activity towards casein and E-cadherin. No cytotoxic effect of either the wild-type, T. forsythia mutants or rHtrA on the viability of host cells was found. In hGFB and U937 macrophages, both T. forsythia species induced an inflammatory response of similar magnitude, as indicated by gene and protein expression of interleukin (IL)-1β, IL-6, IL-8, tumour necrosis factor α and monocyte chemoattractant protein (MCP)-1. Recombinant HtrA had no significant effect on the inflammatory response in hGFBs, whereas in U937 macrophages, it induced a transient inflammatory response at the early stage of infection.

CONCLUSION

HtrA of T. forsythia exhibit proteolytic activity towards the host adhesion molecule E-cadherin and has the potential to influence the host response. Its role in the progression of periodontitis needs further clarification.

Effects of green tea extract epigallocatechin-3-gallate (EGCG) on oral disease-associated microbes: a review

For thousands of years, caries, periodontitis and mucosal diseases, which are closely related to oral microorganisms, have always affected human health and quality of life. These complex microbiota present in different parts of the mouth can cause chronic infections in the oral cavity under certain conditions, some of which can also lead to acute and systemic diseases. With the mutation of related microorganisms and the continuous emergence of drug-resistant strains, in order to prevent and treat related diseases, in addition to the innovation of diagnosis and treatment technology, the development of new antimicrobial drugs is also important. Catechins are polyphenolic compounds in green tea, some of which are reported to provide health benefits for a variety of diseases. Studies have shown that epigallocatechin-3-gallate (EGCG) is the most abundant and effective active ingredient in green tea catechins, which acts against a variety of gram-positive and negative bacteria, as well as some fungi and viruses. This review aims to summarize the research progress on the activity of EGCG against common oral disease-associated organisms and discuss the mechanisms of these actions, hoping to provide new medication strategies for the prevention and treatment of oral infectious diseases, the future research of EGCG and its translation into clinical practice are also discussed.

Inherently and Conditionally Essential Protein Catabolism Genes of Porphyromonas gingivalis

Proteases are critical virulence determinants of Porphyromonas gingivalis, an emerging Alzheimer's disease, cancer, and arthritis pathogen and established agent of periodontitis. Transposon sequencing has been employed to define the core essential genome of this bacterium and genes conditionally essential in multiple environments - abscess formation; epithelial colonization; and cigarette smoke toxin exposure; as well as to elucidate genes required for iron acquisition and a functional type 9 secretion system. Validated and predicted protein catabolism genes identified include a combination of established virulence factors and a larger set of seemingly more mundane proteolytic genes. The functions and relevance of genes that share essentiality in multiple disease-relevant conditions are examined. These common stress-related genes may represent particularly attractive therapeutic targets for the control of P. gingivalis infections.

Variability in Genomic and Virulent Properties of Porphyromonas gingivalis Strains Isolated From Healthy and Severe Chronic Periodontitis Individuals

Porphyromonas gingivalis has been extensively associated with both the onset and progression of periodontitis. We previously isolated and characterized two P. gingivalis strains, one from a patient exhibiting severe chronic periodontitis (CP3) and another from a periodontally healthy individual (H3). We previously showed that CP3 and H3 exhibit differences in virulence since H3 showed a lower resistance to cationic peptides compared with CP3, and a lower ability to induce proliferation in gingival epithelial cells. Here, we aimed to determine whether differences in virulence between these two strains are associated with the presence or absence of specific genes encoding virulence factors. We sequenced the whole genomes of both P. gingivalis CP3 and H3 and conducted a comparative analysis regarding P. gingivalis virulence genetic determinants. To do so, we performed a homology search of predicted protein sequences in CP3 and H3 genomes against the most characterized virulence genes for P. gingivalis available in the literature. In addition, we performed a genomic comparison of CP3 and H3 with all the 62 genomes of P. gingivalis found in NCBI's RefSeq database. This approach allowed us to determine the evolutionary relationships of CP3 and H3 with other virulent and avirulent strains; and additionally, to detect variability in presence/absence of virulence genes among P. gingivalis genomes. Our results show genetic variability in the hemagglutinin genes. While CP3 possesses one copy of hagA and two of hagC, H3 has no hagA and only one copy of hagC. Experimentally, this finding is related to lower in vitro hemmaglutination ability of H3 compared to CP3. Moreover, while CP3 encodes a gene for a major fimbrium subunit FimA type 4 (CP3_00160), H3 possess a FimA type 1 (H3_01400). Such genetic differences are in agreement with both lower biofilm formation ability and less intracellular invasion to oral epithelial cells exhibited by H3, compared with the virulent strain CP3. Therefore, here we provide new results on the genome sequences, comparative genomics analyses, and phenotypic analyses of two P. gingivalis strains. The genomics comparison of these two strains with the other 62 genomes included in the analysis provided relevant results regarding genetic determinants and their association with P. gingivalis virulence.

Tea polyphenols: application in the control of oral microorganism infectious diseases

One of the most popular drinks worldwide, tea is rich in polyphenols and is beneficial to our health because it contributes to the prevention of many diseases. In the human oral cavity, there are more than 750 different species of bacteria living together within dental plaque. Some of the bacteria are pathogens that contribute to the development of oral diseases such as dental caries, periodontitis, pulpitis, mucosal disease, or halitosis through their virulence factors and their metabolites. Until now, many studies have reported that tea polyphenols (TPs) have evident inhibitory effects on some oral pathogenic microorganisms by suppressing pivotal steps of their pathogenic processes. The aim of this review is to summarize the effectiveness and mechanisms of TPs in inhibiting microorganisms, so as to provide new ideas for the prevention and treatment of oral diseases, and to contribute to the global dental public health.

Effects of quorum-sensing inhibition on experimental periodontitis induced by mixed infection in mice

This study aimed to verify, in in vivo settings, whether quorum-sensing inhibition molecules could attenuate alveolar bone loss induced by Porphyromonas gingivalis/Fusobacterium nucleatum co-infection and reduce the bacterial colonization of periodontal tissues. In BALB/c mice, periodontitis was induced through oral inoculation with P. gingivalis and F. nucleatum six times during a 42-d period. Quorum sensing inhibitors (a furanone compound and D-ribose) were administered simultaneously with bacterial infection. Linear and volumetric modifications of interproximal alveolar bone levels were compared between groups using micro-computed tomography. Total bacteria, and P. gingivalis and F. nucleatum DNA in periodontal tissues, were quantified using real-time PCR. Radiographic linear measurements demonstrated a significant reduction of alveolar bone loss, of approximately 40%, in mice treated with quorum sensing inhibitors when compared with the co-infection group. This was confirmed by a significant increase of residual bone volume in the test group. While total bacterial genes in the treatment group significantly decreased by 93% in periodontal tissue samples when quorum sensing inhibitors were administered, no significant differences of P. gingivalis DNA were found. Quorum sensing inhibitors reduced periodontal breakdown and bacterial infection in periodontal tissues after co-infection with P. gingivalis and F. nucleatum.

Green tea catechins potentiate the effect of antibiotics and modulate adherence and gene expression in Porphyromonas gingivalis

OBJECTIVES

A number of studies have brought evidence that green tea catechins may contribute to periodontal health. The objective of this study was to investigate the ability of a green tea extract and its principal constituent epigallocatechin-3-gallate (EGCG) to potentiate the antibacterial effects of antibiotics (metronidazole, tetracycline) against Porphyromonas gingivalis, and to modulate the adherence to oral epithelial cells and expression of genes coding for virulence factors and the high temperature requirement A (HtrA) stress protein in P. gingivalis.

METHODS

A broth microdilution assay was used to determine the antibacterial activity of the green tea extract and EGCG. The synergistic effects of either compounds in association with metronidazole or tetracycline were evaluated using the checkerboard technique. A fluorescent assay was used to determine bacterial adherence to oral epithelial cells. The modulation of gene expression in P. gingivalis was evaluated by quantitative RT-PCR. The Vibrio harveyi bioassay was used for monitoring quorum sensing inhibitory activity.

RESULTS

The MIC values of the green tea extract on P. gingivalis ranged from 250 to 1000 μg/ml, while those of EGCG ranged from 125 to 500 μg/ml. A marked synergistic effect on P. gingivalis growth was observed for the green tea extract or EGCG in combination with metronidazole. Both the green tea extract and EGCG caused a dose-dependent inhibition of P. gingivalis adherence to oral epithelial cells. On the one hand, green tea extract and EGCG dose-dependently inhibited the expression of several P. gingivalis genes involved in host colonization (fimA, hagA, hagB), tissue destruction (rgpA, kgp), and heme acquisition (hem). On the other hand, both compounds increased the expression of the stress protein htrA gene. The ability of the green tea extract and EGCG to inhibit quorum sensing may contribute to the modulation of gene expression.

CONCLUSIONS

This study explored the preventive and therapeutic potential of green tea catechins against periodontal disease. In addition to inhibit growth and adherence of P. gingivalis, a green tea extract and its main constituent EGCG was found to decrease the expression of genes coding for the major virulence factors.

Identification of Enterococcus faecalis antigens specifically expressed in vivo

Objectives

Molecular mechanism of the pathogenicity of Enterococcus faecalis (E. faecalis), a suspected endodontic pathogen, has not yet been adequately elucidated due to limited information on its virulence factors. Here we report the identification of in vivo expressed antigens of E. faecalis by using a novel immunoscreening technique called change-mediated antigen technology (CMAT) and an experimental animal model of endodontic infection.

Materials and Methods

Among 4,500 E. coli recombinant clones screened, 19 positive clones reacted reproducibly with hyperimmune sera obtained from rabbits immunized with E. faecalis cells isolated from an experimental endodontic infection. DNA sequences from 16 of these in vivo-induced (IVI) genes were determined.

Results

Identified protein antigens of E. faecalis included enzymes involved in housekeeping functions, copper resistance protein, putative outer membrane proteins, and proteins of unknown function.

Conclusions

In vivo expressed antigens of E. faecalis could be identified by using a novel immune-screening technique CMAT and an experimental animal model of endodontic infection. Detailed analysis of these IVI genes will lead to a better understanding of the molecular mechanisms involved in the endodontic infection of E. faecalis.

Biogenesis and function of Porphyromonas gingivalis outer membrane vesicles

Porphyromonas gingivalis is one of the keystone pathogens associated with chronic periodontitis. All P. gingivalis strains examined thus far produce outer membrane vesicles. Recent studies have found that vesicles possess some well-known virulence factors of P. gingivalis such as adhesins, toxins and proteolytic enzymes. Carrying most of the characteristic features of their parent P. gingivalis cells, vesicles communicate with host cells and other members of microbial biofilms, resulting in the transmission of virulence factors into these host cells and the formation of pathogenic bacteria-dominated microbial communities. An in-depth understanding of both the nature and role of vesicles in the pathogenicity of P. gingivalis is both important and timely, particularly when speaking of periodontitis and its related systemic effects.

The HtrA-like protease CD3284 modulates virulence of Clostridium difficile

In the past decade, Clostridium difficile has emerged as an important gut pathogen. Symptoms of C. difficile infection range from mild diarrhea to pseudomembranous colitis. Besides the two main virulence factors toxin A and toxin B, other virulence factors are likely to play a role in the pathogenesis of the disease. In other Gram-positive and Gram-negative pathogenic bacteria, conserved high-temperature requirement A (HtrA)-like proteases have been shown to have a role in protein homeostasis and quality control. This affects the functionality of virulence factors and the resistance of bacteria to (host-induced) environmental stresses. We found that the C. difficile 630 genome encodes a single HtrA-like protease (CD3284; HtrA) and have analyzed its role in vivo and in vitro through the creation of an isogenic ClosTron-based htrA mutant of C. difficile strain 630Δerm (wild type). In contrast to the attenuated phenotype seen with htrA deletion in other pathogens, this mutant showed enhanced virulence in the Golden Syrian hamster model of acute C. difficile infection. Microarray data analysis showed a pleiotropic effect of htrA on the transcriptome of C. difficile, including upregulation of the toxin A gene. In addition, the htrA mutant showed reduced spore formation and adherence to colonic cells. Together, our data show that htrA can modulate virulence in C. difficile.

The role of serine protease HtrA in acute ulcerative enterocolitis and extra-intestinal immune responses during Campylobacter jejuni infection of gnotobiotic IL-10 deficient mice

Campylobacter jejuni infections have a high prevalence worldwide and represent a significant socioeconomic burden. C. jejuni can cross the intestinal epithelial barrier as visualized in biopsies derived from human patients and animal models, however, the underlying molecular mechanisms and associated immunopathology are still not well understood. We have recently shown that the secreted serine protease HtrA (high temperature requirement A) plays a key role in C. jejuni cellular invasion and transmigration across polarized epithelial cells in vitro. In the present in vivo study we investigated the role of HtrA during C. jejuni infection of mice. We used the gnotobiotic IL-10^−/− mouse model to study campylobacteriosis following peroral infection with the C. jejuni wild-type (WT) strain NCTC11168 and the isogenic, non-polar NCTC11168ΔhtrA deletion mutant. Six days post infection (p.i.) with either strain mice harbored comparable intestinal C. jejuni loads, whereas ulcerative enterocolitis was less pronounced in mice infected with the ΔhtrA mutant strain. Moreover, ΔhtrA mutant infected mice displayed lower apoptotic cell numbers in the large intestinal mucosa, less colonic accumulation of neutrophils, macrophages and monocytes, lower large intestinal nitric oxide, IFN-γ, and IL-6 as well as lower TNF-α and IL-6 serum concentrations as compared to WT strain infected mice at day 6 p.i. Notably, immunopathological responses were not restricted to the intestinal tract given that liver and kidneys exhibited mild histopathological changes 6 days p.i. with either C. jejuni strain. We also found that hepatic and renal nitric oxide levels or renal TNF-α concentrations were lower in the ΔhtrA mutant as compared to WT strain infected mice. In conclusion, we show here that the C. jejuni HtrA protein plays a pivotal role in inducing host cell apoptosis and immunopathology during murine campylobacteriosis in the gut in vivo.

Periodontal pathogens and atherosclerosis: implications of inflammation and oxidative modification of LDL

Inflammation is well accepted to play a crucial role in the development of atherosclerotic lesions, and recent studies have demonstrated an association between periodontal disease and cardiovascular disease. Porphyromonas gingivalis and Aggregatibacter actinomycetemcomitans, causative agents of destructive chronic inflammation in the periodontium, can accelerate atheroma deposition in animal models. Emerging evidence suggests that vaccination against virulence factors of these pathogens and anti-inflammatory therapy may confer disease resistance. In this review, we focus on the role of inflammatory mechanisms and oxidative modification in the formation and activation of atherosclerotic plaques accelerated by P. gingivalis or A. actinomycetemcomitans in an ApoE-deficient mouse model and high-fat-diet-fed mice. Furthermore, we examine whether mucosal vaccination with a periodontal pathogen or the anti-inflammatory activity of catechins can reduce periodontal pathogen-accelerated atherosclerosis.

Proteomic analysis of Vibrio cholerae outer membrane vesicles

Outer membrane vesicles (OMVs) produced by Gram-negative bacteria provide an interesting research material for defining cell-envelope proteins without experimental cell disruption. OMVs are also promising immunogenic platforms and may play important roles in bacterial survival and pathogenesis. We used in-solution trypsin digestion coupled to mass spectrometry to identify 90 proteins present in OMVs of Vibrio cholerae when grown under conditions that activate the TCP pilus virulence regulatory protein (ToxT) virulence regulon. The ToxT expression profile and potential contribution to virulence of these proteins were assessed using ToxT and in vivo RNA-seq, Tn-seq, and cholera stool proteomic and other genome-wide data sets. Thirteen OMV-associated proteins appear to be essential for cell growth, and therefore may represent antibacterial drug targets. Another 12 nonessential OMV proteins, including DegP protease, were required for intestinal colonization in rabbits. Comparative proteomics of a degP mutant revealed the importance of DegP in the incorporation of nine proteins into OMVs, including ones involved in biofilm matrix formation and various substrates of the type II secretion system. Taken together, these results suggest that DegP plays an important role in determining the content of OMVs and also affects phenotypes such as intestinal colonization, proper function of the type II secretion system, and formation of biofilm matrix.

Identification of a novel bacterial outer membrane interleukin-1Β-binding protein from Aggregatibacter actinomycetemcomitans

Aggregatibacteractinomycetemcomitans is a gram-negative opportunistic oral pathogen. It is frequently associated with subgingival biofilms of both chronic and aggressive periodontitis, and the diseased sites of the periodontium exhibit increased levels of the proinflammatory mediator interleukin (IL)-1β. Some bacterial species can alter their physiological properties as a result of sensing IL-1β. We have recently shown that this cytokine localizes to the cytoplasm of A. actinomycetemcomitans in co-cultures with organotypic gingival mucosa. However, current knowledge about the mechanism underlying bacterial IL-1β sensing is still limited. In this study, we characterized the interaction of A. actinomycetemcomitans total membrane protein with IL-1β through electrophoretic mobility shift assays. The interacting protein, which we have designated bacterial interleukin receptor I (BilRI), was identified through mass spectrometry and was found to be Pasteurellaceae specific. Based on the results obtained using protein function prediction tools, this protein localizes to the outer membrane and contains a typical lipoprotein signal sequence. All six tested biofilm cultures of clinical A. actinomycetemcomitans strains expressed the protein according to phage display-derived antibody detection. Moreover, proteinase K treatment of whole A. actinomycetemcomitans cells eliminated BilRI forms that were outer membrane specific, as determined through immunoblotting. The protein was overexpressed in Escherichia coli in both the outer membrane-associated form and a soluble cytoplasmic form. When assessed using flow cytometry, the BilRI-overexpressing E. coli cells were observed to bind 2.5 times more biotinylated-IL-1β than the control cells, as detected with avidin-FITC. Overexpression of BilRI did not cause binding of a biotinylated negative control protein. In a microplate assay, soluble BilRI bound to IL-1β, but this binding was not specific, as a control protein for IL-1β also interacted with BilRI. Our findings suggest that A. actinomycetemcomitans expresses an IL-1β-binding surface-exposed lipoprotein that may be part of the bacterial IL-1β-sensing system.

Porphyromonas gingivalis strain specific interactions with human coronary artery endothelial cells: a comparative study

Both epidemiologic and experimental findings suggest that infection with Porphyromonas gingivalis exacerbates progression of atherosclerosis. As P. gingivalis exhibits significant strain variation, it is reasonable that different strains possess different capabilities and/or mechanisms by which they promote atherosclerosis. Using P. gingivalis strains that have been previously evaluated in the ApoE null atherosclerosis model, we assessed the ability of W83, A7436, 381, and 33277 to adhere, invade, and persist in human coronary artery endothelial (HCAE) cells. W83 and 381 displayed an equivalent ability to adhere to HCAE cells, which was significantly greater than both A7436 and 33277 (P<0.01). W83, 381, and 33277 were more invasive than A7436 (P<0.0001). However, only W83 and A7436 were able to remain viable up to 48 hours in HCAE cell cultures, whereas 381 was cleared by 48 hours and 33277 was cleared by 24 hours. These differences in persistence were in part due to strain specific differences in intracellular trafficking. Both W83 and 381 trafficked through the autophagic pathway, but not A7436 or 33277. Internalized 381 was the only strain that was dependent upon the autophagic pathway for its survival. Finally, we assessed the efficacy of these strains to activate HCAE cells as defined by production of IL-6, IL-8, IL-12p40, MCP-1, RANTES, TNF-α, and soluble adhesion molecules (sICAM-1, sVCAM-1, and sE-selectin). Only moderate inflammation was observed in cells infected with either W83 or A7436, whereas cells infected with 381 exhibited the most profound inflammation, followed by cells infected with 33277. These results demonstrate that virulence mechanisms among different P. gingivalis strains are varied and that pathogenic mechanisms identified for one strain are not necessarily applicable to other strains.

Differential response of Porphyromonas gingivalis to varying levels and duration of hydrogen peroxide-induced oxidative stress

Porphyromonas gingivalis, an anaerobic oral pathogen implicated in adult periodontitis, can exist in an environment of oxidative stress. To evaluate its adaptation to this environment, we have assessed the response of P. gingivalis W83 to varying levels and durations of hydrogen peroxide (H(2)O(2))-induced stress. When P. gingivalis was initially exposed to a subinhibitory concentration of H(2)O(2) (0.1 mM), an adaptive response to higher concentrations could be induced. Transcriptome analysis demonstrated that oxidative stress can modulate several functional classes of genes depending on the severity and duration of the exposure. A 10 min exposure to H(2)O(2) revealed increased expression of genes involved in DNA damage and repair, while after 15 min, genes involved in protein fate, protein folding and stabilization were upregulated. Approximately 9 and 2.8% of the P. gingivalis genome displayed altered expression in response to H(2)O(2) exposure at 10 and 15 min, respectively. Substantially more genes were upregulated (109 at 10 min; 47 at 15 min) than downregulated (76 at 10 min; 11 at 15 min) by twofold or higher in response to H(2)O(2) exposure. The majority of these modulated genes were hypothetical or of unknown function. One of those genes (pg1372) with DNA-binding properties that was upregulated during prolonged oxidative stress was inactivated by allelic exchange mutagenesis. The isogenic mutant P. gingivalis FLL363 (pg1372 : : ermF) showed increased sensitivity to H(2)O(2) compared with the parent strain. Collectively, our data indicate the adaptive ability of P. gingivalis to oxidative stress and further underscore the complex nature of its resistance strategy under those conditions.

Comprehensive transcriptome analysis of the periodontopathogenic bacterium Porphyromonas gingivalis W83

High-density tiling microarray and RNA sequencing technologies were used to analyze the transcriptome of the periodontopathogenic bacterium Porphyromonas gingivalis. The compiled P. gingivalis transcriptome profiles were based on total RNA samples isolated from three different laboratory culturing conditions, and the strand-specific transcription profiles generated covered the entire genome, including both protein coding and noncoding regions. The transcription profiles revealed various operon structures, 5'- and 3'-end untranslated regions (UTRs), differential expression patterns, and many novel, not-yet-annotated transcripts within intergenic and antisense regions. Further transcriptome analysis identified the majority of the genes as being expressed within operons and most 5' and 3' ends to be protruding UTRs, of which several 3' UTRs were extended to overlap genes carried on the opposite/antisense strand. Extensive antisense RNAs were detected opposite most insertion sequence (IS) elements. Pairwise comparative analyses were also performed among transcriptome profiles of the three culture conditions, and differentially expressed genes and metabolic pathways were identified. With the growing realization that noncoding RNAs play important biological functions, the discovery of novel RNAs and the comprehensive transcriptome profiles compiled in this study may provide a foundation to further understand the gene regulation and virulence mechanisms in P. gingivalis. The transcriptome profiles can be viewed at and downloaded from the Microbial Transcriptome Database website, http://bioinformatics.forsyth.org/mtd.

Genomic comparison of invasive and rare non-invasive strains reveals Porphyromonas gingivalis genetic polymorphisms

Background

Porphyromonas gingivalis strains are shown to invade human cells in vitro with different invasion efficiencies, varying by up to three orders of magnitude.

Objective

We tested the hypothesis that invasion-associated interstrain genomic polymorphisms are present in P. gingivalis and that putative invasion-associated genes can contribute to P. gingivalis invasion.

Design

Using an invasive (W83) and the only available non-invasive P. gingivalis strain (AJW4) and whole genome microarrays followed by two separate software tools, we carried out comparative genomic hybridization (CGH) analysis.

Results

We identified 68 annotated and 51 hypothetical open reading frames (ORFs) that are polymorphic between these strains. Among these are surface proteins, lipoproteins, capsular polysaccharide biosynthesis enzymes, regulatory and immunoreactive proteins, integrases, and transposases often with abnormal GC content and clustered on the chromosome. Amplification of selected ORFs was used to validate the approach and the selection. Eleven clinical strains were investigated for the presence of selected ORFs. The putative invasion-associated ORFs were present in 10 of the isolates. The invasion ability of three isogenic mutants, carrying deletions in PG0185, PG0186, and PG0982 was tested. The PG0185 (ragA) and PG0186 (ragB) mutants had 5.1×10³-fold and 3.6×10³-fold decreased in vitro invasion ability, respectively.

Conclusion

The annotation of divergent ORFs suggests deficiency in multiple genes as a basis for P. gingivalis non-invasive phenotype.

Cloning, expression and characterisation of an HtrA-like serine protease produced in vivo by Mycobacterium leprae

Members of the high temperature requirement A (HtrA) family of chaperone proteases have been shown to play a role in bacterial pathogenesis. In a recent report, we demonstrated that the gene ML0176, which codes for a predicted HtrA-like protease, a gene conserved in other species of mycobacteria, is transcribed by Mycobacterium leprae in human leprosy lesions. In the present study, the recombinant ML0176 protein was produced and its enzymatic properties investigated. M. lepraerecombinant ML0176 was able to hydrolyse a variety of synthetic and natural peptides. Similar to other HtrA proteins, this enzyme displayed maximum proteolytic activity at temperatures above 40 degrees C and was completely inactivated by aprotinin, a protease inhibitor with high selectivity for serine proteases. Finally, analysis of M. leprae ML0176 specificity suggested a broader cleavage preference than that of previously described HtrAs homologues. In summary, we have identified an HtrA-like protease in M. lepraethat may constitute a potential new target for the development of novel prophylactic and/or therapeutic strategies against mycobacterial infections.

A member of the peptidase M48 superfamily of Porphyromonas gingivalis is associated with virulence in vitro and in vivo

Background

In vivo-induced antigen technology was previously used to identify 115 genes induced in Porphyromonas gingivalis W83 during human infection. One of these, PG2197, a conserved hypothetical protein which has homology to a Zn-dependent protease, was examined with respect to a role in disease.

Design

The expression of PG2197 in human periodontitis patients was investigated, but as there is increasing evidence of a direct relationship between P. gingivalis and cardiovascular disease, a mutation was constructed in this gene to also determine its role in adherence, invasion, and persistence within human coronary artery endothelial cells (HCAEC) and neutrophil killing susceptibility.

Results

Plaque samples from 20 periodontitis patients were analyzed by real-time PCR, revealing that PG2197 was expressed in 60.0% of diseased sites compared to 15.8% of healthy sites, even though P. gingivalis was detected in equal numbers from both sites. The expression of this gene was also found to be up-regulated in microarrays at 5 and 30 min of invasion of HCAEC. Interestingly, a PG2197 mutant displayed increased adherence, invasion, and persistence within HCAEC when compared to the wild-type strain.

Conclusion

This gene appears to be important for the virulence of P. gingivalis, both in vivo and in vitro.

Quantitative detection of periodontopathic bacteria in atherosclerotic plaques from coronary arteries

Oral pathogens, including periodontopathic bacteria, are thought to be aetiological factors in the development of cardiovascular disease. In this study, the presence of Aggregatibacter actinomycetemcomitans, Fusobacterium nucleatum-periodonticum-simiae group, Porphyromonas gingivalis, Prevotella intermedia, Prevotella nigrescens and Tannerella forsythia in atheromatous plaques from coronary arteries was determined by real-time PCR. Forty-four patients displaying cardiovascular disease were submitted to periodontal examination and endarterectomy of coronary arteries. Approximately 60-100 mg atherosclerotic tissue was removed surgically and DNA was obtained. Quantitative detection of periodontopathic bacteria was performed using universal and species-specific TaqMan probe/primer sets. Total bacterial and periodontopathic bacterial DNA were found in 94.9 and 92.3 %, respectively, of the atheromatous plaques from periodontitis patients, and in 80.0 and 20.0 %, respectively, of atherosclerotic tissues from periodontally healthy subjects. All periodontal bacteria except for the F. nucleatum-periodonticum-simiae group were detected, and their DNA represented 47.3 % of the total bacterial DNA obtained from periodontitis patients. Porphyromonas gingivalis, A. actinomycetemcomitans and Prevotella intermedia were detected most often. The presence of two or more periodontal species could be observed in 64.1 % of the samples. In addition, even in samples in which a single periodontal species was detected, additional unidentified microbial DNA could be observed. The significant number of periodontopathic bacterial DNA species in atherosclerotic tissue samples from patients with periodontitis suggests that the presence of these micro-organisms in coronary lesions is not coincidental and that they may in fact contribute to the development of vascular diseases.

Comparative transcriptomic analysis of Porphyromonas gingivalis biofilm and planktonic cells

BACKGROUND

Porphyromonas gingivalis in subgingival dental plaque, as part of a mature biofilm, has been strongly implicated in the onset and progression of chronic periodontitis. In this study using DNA microarray we compared the global gene expression of a P. gingivalis biofilm with that of its planktonic counterpart grown in the same continuous culture.

RESULTS

Approximately 18% (377 genes, at 1.5 fold or more, P-value < 0.01) of the P. gingivalis genome was differentially expressed when the bacterium was grown as a biofilm. Genes that were down-regulated in biofilm cells, relative to planktonic cells, included those involved in cell envelope biogenesis, DNA replication, energy production and biosynthesis of cofactors, prosthetic groups and carriers. A number of genes encoding transport and binding proteins were up-regulated in P. gingivalis biofilm cells. Several genes predicted to encode proteins involved in signal transduction and transcriptional regulation were differentially regulated and may be important in the regulation of biofilm growth.

CONCLUSION

This study analyzing global gene expression provides insight into the adaptive response of P. gingivalis to biofilm growth, in particular showing a down regulation of genes involved in growth and metabolic activity.