Tannerella forsythia, a periodontal pathogen entering the genomic era

A Flagellin-Adjuvanted Trivalent Mucosal Vaccine Targeting Key Periodontopathic Bacteria

Periodontal disease (PD) is caused by microbial dysbiosis and accompanying adverse inflammatory responses. Due to its high incidence and association with various systemic diseases, disease-modifying treatments that modulate dysbiosis serve as promising therapeutic approaches. In this study, to simulate the pathophysiological situation, we established a "temporary ligature plus oral infection model" that incorporates a temporary silk ligature and oral infection with a cocktail of live Tannerella forsythia (Tf), Pophyromonas gingivalis (Pg), and Fusobacterium nucleatum (Fn) in mice and tested the efficacy of a new trivalent mucosal vaccine. It has been reported that Tf, a red complex pathogen, amplifies periodontitis severity by interacting with periodontopathic bacteria such as Pg and Fn. Here, we developed a recombinant mucosal vaccine targeting a surface-associated protein, BspA, of Tf by genetically combining truncated BspA with built-in adjuvant flagellin (FlaB). To simultaneously induce Tf-, Pg-, and Fn-specific immune responses, it was formulated as a trivalent mucosal vaccine containing Tf-FlaB-tBspA (BtB), Pg-Hgp44-FlaB (HB), and Fn-FlaB-tFomA (BtA). Intranasal immunization with the trivalent mucosal vaccine (BtB + HB + BtA) prevented alveolar bone loss and gingival proinflammatory cytokine production. Vaccinated mice exhibited significant induction of Tf-tBspA-, Pg-Hgp44-, and Fn-tFomA-specific IgG and IgA responses in the serum and saliva, respectively. The anti-sera and anti-saliva efficiently inhibited epithelial cell invasion by Tf and Pg and interfered with biofilm formation by Fn. The flagellin-adjuvanted trivalent mucosal vaccine offers a novel method for modulating dysbiotic bacteria associated with periodontitis. This approach leverages the adjuvant properties of flagellin to enhance the immune response, aiming to restore a balanced microbial environment and improve periodontal health.

Bioorthogonal Labeling and Click-Chemistry-Based Visualization of the Tannerella forsythia Cell Wall

The objective of this chapter is to provide a detailed protocol for the peptidoglycan (cell wall) labeling of the periodontal pathogen Tannerella forsythia and the development of a laboratory-safe Escherichia coli strain utilizing the N-acetylmuramic acid recycling enzymes AmgK, N-acetylmuramate/N-acetylglucosamine kinase, and MurU, N-acetylmuramate alpha-1-phosphate uridylyltransferase, from T. forsythia. The procedure involves bioorthogonal labeling of bacterial cells with an azido-modified analog of the amino sugar, N-acetylmuramic acid, through "click chemistry" with a fluorescent dye. The protocol is suitable for the generation of fluorescently labeled peptidoglycan molecules for applications in the study of bacterial and peptidoglycan trafficking in the host cells and cell wall recycling in complex microbiomes.

Oral microbial communities in children, caregivers, and associations with salivary biomeasures and environmental tobacco smoke exposure

Human oral microbial communities are diverse, with implications for oral and systemic health. Oral microbial communities change over time; thus, it is important to understand how healthy versus dysbiotic oral microbiomes differ, especially within and between families. There is also a need to understand how the oral microbiome composition is changed within an individual including by factors such as environmental tobacco smoke (ETS) exposure, metabolic regulation, inflammation, and antioxidant potential. Using archived saliva samples collected from caregivers and children during a 90-month follow-up assessment in a longitudinal study of child development in the context of rural poverty, we used 16S rRNA gene sequencing to determine the salivary microbiome. A total of 724 saliva samples were available, 448 of which were from caregiver/child dyads, an additional 70 from children and 206 from adults. We compared children's and caregivers' oral microbiomes, performed "stomatotype" analyses, and examined microbial relations with concentrations of salivary markers associated with ETS exposure, metabolic regulation, inflammation, and antioxidant potential (i.e., salivary cotinine, adiponectin, C-reactive protein, and uric acid) assayed from the same biospecimens. Our results indicate that children and caregivers share much of their oral microbiome diversity, but there are distinct differences. Microbiomes from intrafamily individuals are more similar than microbiomes from nonfamily individuals, with child/caregiver dyad explaining 52% of overall microbial variation. Notably, children harbor fewer potential pathogens than caregivers, and participants' microbiomes clustered into two groups, with major differences being driven by Streptococcus spp. Differences in salivary microbiome composition associated with ETS exposure, and taxa associated with salivary analytes representing potential associations between antioxidant potential, metabolic regulation, and the oral microbiome. IMPORTANCE The human oral cavity is a multi-environment habitat that harbors a diversity of microorganisms. This oral microbiome is often transmitted between cohabitating individuals, which may associate oral and systemic health within family members. Furthermore, family social ecology plays a significant role in childhood development, which may be associated with lifelong health outcomes. In this study, we collected saliva from children and their caregivers and used 16S rRNA gene sequencing to characterize their oral microbiomes. We also analyzed salivary biomeasures of environmental tobacco smoke exposure, metabolic regulation, inflammation, and antioxidant potential. We show there are differences in individuals' oral microbiomes mainly due to Streptococcus spp. that family members share much of their microbes, and several bacterial taxa associate with the selected salivary biomeasures. Our results suggest there are large-scale oral microbiome patterns, and there are likely relationships between oral microbiomes and the social ecology of families.

Bacterial Sialic Acid Catabolism at the Host–Microbe Interface

Sialic acids consist of nine-carbon keto sugars that are commonly found at the terminal end of mucins. This positional feature of sialic acids contributes to host cell interactions but is also exploited by some pathogenic bacteria in evasion of host immune system. Moreover, many commensals and pathogens use sialic acids as an alternative energy source to survive within the mucus-covered host environments, such as the intestine, vagina, and oral cavity. Among the various biological events mediated by sialic acids, this review will focus on the processes necessary for the catabolic utilization of sialic acid in bacteria. First of all, transportation of sialic acid should be preceded before its catabolism. There are four types of transporters that are used for sialic acid uptake; the major facilitator superfamily (MFS), the tripartite ATP-independent periplasmic C4-dicarboxilate (TRAP) multicomponent transport system, the ATP binding cassette (ABC) transporter, and the sodium solute symporter (SSS). After being moved by these transporters, sialic acid is degraded into an intermediate of glycolysis through the well-conserved catabolic pathway. The genes encoding the catabolic enzymes and transporters are clustered into an operon(s), and their expression is tightly controlled by specific transcriptional regulators. In addition to these mechanisms, we will cover some researches about sialic acid utilization by oral pathogens.

Prevalence of Periodontal Pathogens in Slovak Patients with Periodontitis and Their Possible Aspect of Transmission from Companion Animals to Humans

Oral health and diseases are greatly influenced by oral bacteria. During dysbiosis, bacterial composition changes, which can lead to periodontitis. Periodontitis in humans is associated with periodontal pathogens such as Treponema denticola, Porphyromonas gingivalis, Tannerella forsythia and Aggregatibacter actinomycetemcomitans. Animal-to-human transmission of some of these pathogens has also been reported. The aim of this study was to evaluate the prevalence of periodontal pathogens in Slovak patients and to assess the possible risk of transmission of these pathogens from animals to their owners. The presence of periodontal pathogens in dental plaque was monitored by PCR. Amplified products were analysed using Sanger sequencing. T. forsythia isolates were assessed for the susceptibility to different antibiotics using the disk diffusion method. In humans, T. denticola, P. gingivalis, T. forsythia and A. actinomycetemcomitans were present in 69.23%, 69.23%, 100% and 84.62%, respectively. Most isolates of T. forsythia were susceptible to amoxicillin-clavulanic acid, clindamycin and moxifloxacin, but they were resistant to metronidazole. The transmission of T. forsythia from animals to their owners was not proven based on sequence analysing. On the other hand, transmission of Porphyromonas gulae was confirmed, but the risk of its involvement in the pathogenesis of periodontitis in humans must be further investigated.

Investigating Peptidoglycan Recycling Pathways in Tannerella forsythia with N-Acetylmuramic Acid Bioorthogonal Probes

The human oral microbiome is the second largest microbial community in humans, harboring over 700 bacterial species, which aid in digestion and protect from growth of disease-causing pathogens. One such oral pathogen, Tannerella forsythia, along with other species, contributes to the pathogenesis of periodontitis. T. forsythia is unable to produce its own N-acetylmuramic acid (NAM) sugar, essential for peptidoglycan biosynthesis and therefore must scavenge NAM from other species with which it cohabitates. Here, we explore the recycling potential of T. forsythia for NAM uptake with a bioorthogonal modification into its peptidoglycan, allowing for click-chemistry-based visualization of the cell wall structure. Additionally, we identified NAM recycling enzyme homologues in T. forsythia that are similar to the enzymes found in Pseudomonas putida. These homologues were then genetically transformed into a laboratory safe Escherichia coli strain, resulting in the efficient incorporation of unnatural NAM analogues into the peptidoglycan backbone and its visualization, alone or in the presence of human macrophages. This strain will be useful in further studies to probe NAM recycling and peptidoglycan scavenging pathways of T. forsythia and other cohabiting bacteria.

The Association between Tannerella forsythia and the Onset of Fever in Older Nursing Home Residents: A Prospective Cohort Study

Background: Periodontal pathogens are related to the incidence of systemic diseases. This study aimed to examine whether periodontal pathogen burden is associated with the risk of fever onset in older adults. Methods: Older adults in nursing homes, aged ≥65 years, were enrolled. The study was set in Kitakyushu, Japan. The body temperatures of participants were ≥37.2 °C and were recorded for eight months. As periodontal pathogens, Porphyromonas gingivalis, Treponema denticola, and Tannerella forsythia were qualified by a real-time polymerase chain reaction at the baseline. For statistical analysis, the number of bacterial counts was logarithmically conversed to 10 as a base. Results: Data from 56 participants with a median age of 88 (62−98) years were available for analysis. The logarithmic-conversed bacterial counts of T. forsythia, but not P. gingivalis or T. denticola, were associated with the onset of fever in older residents. The Kaplan−Meier method revealed that the group with <104 of T. forsythia had significantly less cumulative fever incidence than the group with ≥104 of T. forsythia. The group with ≥104 of T. forsythia was associated with an increased risk of fever onset (hazard ratio, 3.7; 98% confidence interval, 1.3−10.2; p = 0.012), which was adjusted for possible confounders. Conclusions: Bacterial burden of T. forsythia in the oral cavity was associated with the risk of the onset of fever in older nursing homes residents.

Tannerella forsythia strains differentially induce interferon gamma-induced protein 10 (IP-10) expression in macrophages due to lipopolysaccharide heterogeneity

Tannerella forsythia is strongly implicated in the development of periodontitis, an inflammatory disease that destroys the bone and soft tissues supporting the tooth.  To date, the knowledge of the virulence attributes of T. forsythia species has mainly come from studies with a laboratory adapted strain (ATCC 43 037). In this study, we focused on two T. forsythia clinical isolates, UB4 and UB20, in relation to their ability to activate macrophages. We found that these clinical isolates differentially induced proinflammatory cytokine expression in macrophages. Prominently, the expression of the chemokine protein IP-10 (CXCL10) was highly induced by UB20 as compared to UB4 and the laboratory strain ATCC 43 037. Our study focused on the lipopolysaccharide component (LPS) of these strains and found that UB20 expressed a smooth-type LPS, unlike UB4 and ATCC 43 037 each of which expressed a rough-type LPS. The LPS from UB20, via activation of TLR4, was found to be a highly potent inducer of IP-10 expression via signaling through STAT1 (signal transducer and activator of transcription-1). These data suggest that pathogenicity of T. forsythia species could be strain dependent and the LPS heterogeneity associated with the clinical strains might be responsible for their pathogenic potential and severity of periodontitis.

Dental chews positively shift the oral microbiota of adult dogs

Microbiota plays a prominent role in periodontal disease, but the canine oral microbiota and how dental chews may affect these populations have been poorly studied. We aimed to determine the differences in oral microbiota of adult dogs consuming dental chews compared with control dogs consuming only a diet. Twelve adult female beagle dogs (mean age = 5.31 ± 1.08 yr) were used in a replicated 4 × 4 Latin square design consisting of 28-d periods. Treatments (n = 12/group) included: diet only (CT); diet + Bones & Chews Dental Treats (BC; Chewy, Inc., Dania Beach, FL); diet + Dr. Lyon's Grain-Free Dental Treats (DL; Dr. Lyon's, LLC, Dania Beach, FL); and diet + Greenies Dental Treats (GR; Mars Petcare US, Franklin, TN). Each day, one chew was provided 4 h after mealtime. On day 27, breath samples were analyzed for total volatile sulfur compound concentrations using a Halimeter. On day 0 of each period, teeth were cleaned by a veterinary dentist blinded to treatments. Teeth were scored for plaque, calculus, and gingivitis by the same veterinary dentist on day 28 of each period. After scoring, salivary (SAL), subgingival (SUB), and supragingival (SUP) samples were collected for microbiota analysis using Illumina MiSeq. All data were analyzed using SAS (version 9.4) using the Mixed Models procedure, with P < 0.05 considered significant. All dogs consuming chews had lower calculus coverage and thickness, pocket depth and bleeding, plaque thickness, and halitosis compared with CT. In all sites of collection, CT dogs had a higher relative abundance of one or more potentially pathogenic bacteria (Porphyromonas, Anaerovorax, Desulfomicrobium, Tannerella, and Treponema) and lower relative abundance of one or more genera associated with oral health (Neisseria, Corynebacterium, Capnocytophaga, Actinomyces, Lautropia, Bergeyella, and Moraxella) than those fed chews. DL reduced Porphyromonas in SUP and SUB samples. DL and GR reduced Treponema in SUP samples. DL increased Corynebacterium in all sites of collection. BC increased Corynebacterium in SAL samples. DL and GR increased Neisseria in SAL samples. DL increased Actinomyces in the SUB sample. GR increased Actinomyces in SAL samples. Our results suggest that the dental chews tested in this study may aid in reducing periodontal disease risk in dogs by beneficially shifting the microbiota inhabiting plaque and saliva of a dog's oral cavity. These shifts occurred over a short period of time and were correlated with improved oral health scores.

Protective Action of L. salivarius SGL03 and Lactoferrin against COVID-19 Infections in Human Nasopharynx

In this study, we used live viral particles from oral secretions from 17 people infected with SARS-CoV-2 and from 17 healthy volunteers, which were plated on a suitable medium complete for all microorganisms and minimal for L.salivarius growth. Both types of media also contained an appropriately prepared vector system pGEM-5Zf (+) based on the lactose operon (beta-galactosidase system). Incubation was carried out on both types of media for 24 h with the addition of 200 μL of Salistat SGL03 solution in order to test its inhibitory effect on the coronavirus contained in the oral mucosa and nasopharynx, visible as light blue virus particles on the test plates, which gradually disappeared in the material collected from infected persons over time. Regardless of the conducted experiments, swabs were additionally taken from the nasopharynx of infected and healthy people after rinsing the throat and oral mucosa with Salistat SGL03. In both types of experiments, after 24 h of incubation on appropriate media with biological material, we did not find any virus particles. Results were also confirmed by MIC and MBC tests. Results prove that lactoferrin, as one of the ingredients of the preparation, is probably a factor that blocks the attachment of virus particles to the host cells, determining its anti-viral properties. The conducted preliminary experiments constitute a very promising model for further research on the anti-viral properties of the ingredients contained in the Salistat SGL03 dietary supplement.

Microbiota populations in supragingival plaque, subgingival plaque, and saliva habitats of adult dogs

Background

Oral diseases are common in dogs, with microbiota playing a prominent role in the disease process. Oral cavity habitats harbor unique microbiota populations that have relevance to health and disease. Despite their importance, the canine oral cavity microbial habitats have been poorly studied. The objectives of this study were to (1) characterize the oral microbiota of different habitats of dogs and (2) correlate oral health scores with bacterial taxa and identify what sites may be good options for understanding the role of microbiota in oral diseases. We used next-generation sequencing to characterize the salivary (SAL), subgingival (SUB), and supragingival (SUP) microbial habitats of 26 healthy adult female Beagle dogs (4.0 ± 1.2 year old) and identify taxa associated with periodontal disease indices.

Results

Bacterial species richness was highest for SAL, moderate for SUB, and lowest for SUP samples (p < 0.001). Unweighted and weighted principal coordinates plots showed clustering by habitat, with SAL and SUP samples being the most different from one another. Bacteroidetes, Proteobacteria, Firmicutes, Fusobacteria, Actinobacteria, and Spirochaetes were the predominant phyla in all habitats. Paludibacter, Filifactor, Peptostreptococcus, Fusibacter, Anaerovorax, Fusobacterium, Leptotrichia, Desulfomicrobium, and TG5 were enriched in SUB samples, while Actinomyces, Corynebacterium, Leucobacter, Euzebya, Capnocytophaga, Bergeyella, Lautropia, Lampropedia, Desulfobulbus, Enhydrobacter, and Moraxella were enriched in SUP samples. Prevotella, SHD-231, Helcococcus, Treponema, and Acholeplasma were enriched in SAL samples. p-75-a5, Arcobacter, and Pasteurella were diminished in SUB samples. Porphyromonas, Peptococcus, Parvimonas, and Campylobacter were diminished in SUP samples, while Tannerella, Proteocalla, Schwartzia, and Neisseria were diminished in SAL samples. Actinomyces, Corynebacterium, Capnocytophaga, Leptotrichia, and Neisseria were associated with higher oral health scores (worsened health) in plaque samples.

Conclusions

Our results demonstrate the differences that exist among canine salivary, subgingival plaque and supragingival plaque habitats. Salivary samples do not require sedation and are easy to collect, but do not accurately represent the plaque populations that are most important to oral disease. Plaque Actinomyces, Corynebacterium, Capnocytophaga, Leptotrichia, and Neisseria were associated with higher (worse) oral health scores. Future studies analyzing samples from progressive disease stages are needed to validate these results and understand the role of bacteria in periodontal disease development.

The sialyl-O-acetylesterase NanS of Tannerella forsythia encompasses two catalytic modules with different regiospecificity for O7 and O9 of sialic acid

The periodontal pathogen Tannerella forsythia utilizes host sialic acids as a nutrient source. To also make O-acetylated sialyl residues susceptible to the action of its sialidase and sialic acid up-take system, Tannerella produces NanS, an O-acetylesterase with two putative catalytic domains. Here, we analyzed NanS by homology modeling, predicted a catalytic serine-histidine-aspartate triad for each catalytic domain and performed individual domain inactivation by single alanine exchanges of the triad nucleophiles S32 and S311. Subsequent functional analyses revealed that both domains possess sialyl-O-acetylesterase activity, but differ in their regioselectivity with respect to position O9 and O7 of sialic acid. The 7-O-acetylesterase activity inherent to the C-terminal domain of NanS is unique among sialyl-O-acetylesterases and fills the current gap in tools targeting 7-O-acetylation. Application of the O7-specific variant NanS-S32A allowed us to evidence the presence of cellular 7,9-di-O-acetylated sialoglycans by monitoring the gain in 9-O-acetylation upon selective removal of acetyl groups from O7. Moreover, we established de-7,9-O-acetylation by wild-type NanS as an easy and efficient method to validate the specific binding of three viral lectins commonly used for the recognition of (7),9-O-acetylated sialoglycans. Their binding critically depends on an acetyl group in O9, yet de-7,9-O-acetylation proved advantageous over de-9-O-acetylation as the additional removal of the 7-O-acetyl group eliminated ligand formation by 7,9-ester migration. Together, our data show that NanS gained dual functionality through recruitment of two esterase modules with complementary activities. This enables Tannerella to scavenge 7,9-di-O-acetylated sialyl residues and provides a novel, O7-specific tool for studying sialic acid O-acetylation.

Utilization of different MurNAc sources by the oral pathogen Tannerella forsythia and role of the inner membrane transporter AmpG

BACKGROUND

The Gram-negative oral pathogen Tannerella forsythia strictly depends on the external supply of the essential bacterial cell wall sugar N-acetylmuramic acid (MurNAc) for survival because of the lack of the common MurNAc biosynthesis enzymes MurA/MurB. The bacterium thrives in a polymicrobial biofilm consortium and, thus, it is plausible that it procures MurNAc from MurNAc-containing peptidoglycan (PGN) fragments (muropeptides) released from cohabiting bacteria during natural PGN turnover or cell death. There is indirect evidence that in T. forsythia, an AmpG-like permease (Tanf_08365) is involved in cytoplasmic muropeptide uptake. In E. coli, AmpG is specific for the import of N-acetylglucosamine (GlcNAc)-anhydroMurNAc(-peptides) which are common PGN turnover products, with the disaccharide portion as a minimal requirement. Currently, it is unclear which natural, complex MurNAc sources T. forsythia can utilize and which role AmpG plays therein.

RESULTS

We performed a screen of various putative MurNAc sources for T. forsythia mimicking the situation in the natural habitat and compared bacterial growth and cell morphology of the wild-type and a mutant lacking AmpG (T. forsythia ΔampG). We showed that supernatants of the oral biofilm bacteria Porphyromonas gingivalis and Fusobacterium nucleatum, and of E. coli ΔampG, as well as isolated PGN and defined PGN fragments obtained after enzymatic digestion, namely GlcNAc-anhydroMurNAc(-peptides) and GlcNAc-MurNAc(-peptides), could sustain growth of T. forsythia wild-type, while T. forsythia ΔampG suffered from growth inhibition. In supernatants of T. forsythia ΔampG, the presence of GlcNAc-anhMurNAc and, unexpectedly, also GlcNAc-MurNAc was revealed by tandem mass spectrometry analysis, indicating that both disaccharides are substrates of AmpG. The importance of AmpG in the utilization of PGN fragments as MurNAc source was substantiated by a significant ampG upregulation in T. forsythia cells cultivated with PGN, as determined by quantitative real-time PCR. Further, our results indicate that PGN-degrading amidase, lytic transglycosylase and muramidase activities in a T. forsythia cell extract are involved in PGN scavenging.

CONCLUSION

T. forsythia metabolizes intact PGN as well as muropeptides released from various bacteria and the bacterium's inner membrane transporter AmpG is essential for growth on these MurNAc sources, and, contrary to the situation in E. coli, imports both, GlcNAc-anhMurNAc and GlcNAc-MurNAc fragments.

Effect of Ligilactobacillus salivarius and Other Natural Components against Anaerobic Periodontal Bacteria

In this present study, the bacteriostatic effect of Salistat SGL03 and the Lactobacillus salivarius strain contained in it was investigated in adults in in vivo and in vitro tests on selected red complex bacteria living in the subgingival plaque, inducing a disease called periodontitis, i.e., chronic periodontitis. Untreated periodontitis can lead to the destruction of the gums, root cementum, periodontium, and alveolar bone. Anaerobic bacteria, called periopathogens or periodontopathogens, play a key role in the etiopathogenesis of periodontitis. The most important periopathogens of the oral microbiota are: Porphyromonas gingivalis, Tannerella forsythia, Treponema denticola and others. Our hypothesis was verified by taking swabs of scrapings from the surface of the teeth of female hygienists (volunteers) on full and selective growth media for L. salivarius. The sizes of the zones of growth inhibition of periopathogens on the media were measured before (in vitro) and after consumption (in vivo) of Salistat SGL03, based on the disk diffusion method, which is one of the methods of testing antibiotic resistance and drug susceptibility of pathogenic microorganisms. Additionally, each of the periopathogens analyzed by the reduction inoculation method, was treated with L. salivarius contained in the SGL03 preparation and incubated together in Petri dishes. The bacteriostatic activity of SGL03 preparation in selected periopathogens was also analyzed using the minimum inhibition concentration (MIC) and minimum bactericidal concentration (MBC) tests. The obtained results suggest the possibility of using the Salistat SGL03 dietary supplement in the prophylaxis and support of the treatment of periodontitis-already treated as a civilization disease.

Purification of Tannerella forsythia Surface-Layer (S-Layer) Proteins

The objective of this chapter is to provide a detailed purification protocol for the surface-layer (S-layer) glycoproteins of the periodontal pathogen Tannerella forsythia. The procedure involves detergent based solubilization of the bacterial S-layer followed by cesium chloride gradient centrifugation and gel permeation chromatography. The protocol is suitable for the isolation of S-layer glycoproteins from T. forsythia strains with diverse O-glycan structures, and aid in understanding the biochemical basis and the role of protein O-glycosylation in bacterial pathogenesis.

Crystal structure of Type IX secretion system PorE C-terminal domain from Porphyromonas gingivalis in complex with a peptidoglycan fragment

Porphyromonas gingivalis, the major human pathogen associated to periodontal diseases, utilizes the Bacteroidetes-specific type IX secretion system (T9SS) to export virulence factors. PorE is a periplasmic multi-domain lipoprotein associated to the outer membrane that was recently identified as essential for T9SS function. Little is known on T9SS at the structural level, and in particular its interaction with peptidoglycan. This prompted us to carry out structural studies on PorE full length as well as on its four isolated domains. Here we report the crystal structure of the C-terminal OmpA_C-like putative peptidoglycan-binding domain at 1.55 Å resolution. An electron density volume was identified in the protein cleft, making it possible to build a naturally-occurring peptidoglycan fragment. This result suggests that PorE interacts with peptidoglycan and that PorE could anchor T9SS to the cell wall.

Persistence of Tannerella forsythia and Fusobacterium nucleatum in dental plaque: a strategic alliance

PURPOSE OF REVIEW

The Gram-negative oral pathogen Tannerella forsythia is implicated in the pathogenesis of periodontitis, an inflammatory disease characterized by progressive destruction of the tooth supporting structures affecting over 700 million people worldwide. This review highlights the basis of why and how T. forsythia interacts with Fusobacterium nucleatum, a bacterium considered to be a bridge between the early and late colonizing bacteria of the dental plaque.

RECENT FINDINGS

The recent findings indicate that these two organisms have a strong mutualistic relationship that involves foraging by T. forsythia on F. nucleatum peptidoglycan and utilization of glucose, released by the hydrolytic activity of T. forsythia glucanase, as a nutrient by F. nucleatum. In addition, T. forsythia has the unique ability to generate a toxic and inflammogenic compound, methylglyoxal, from glucose. This compound can induce inflammation, leading to the degradation of periodontal tissues and release of host components as nutrients for bacteria to further exacerbate the disease.

SUMMARY

In summary, this article will present our current understanding of mechanisms underpinning T. forsythia-F. nucleatum mutualism, and how this mutualism might impact periodontal disease progression.

Structure-based mechanism of cysteine-switch latency and of catalysis by pappalysin-family metallopeptidases

Tannerella forsythia is an oral dysbiotic periodontopathogen involved in severe human periodontal disease. As part of its virulence factor armamentarium, at the site of colonization it secretes mirolysin, a metallopeptidase of the unicellular pappalysin family, as a zymogen that is proteolytically auto-activated extracellularly at the Ser54-Arg55 bond. Crystal structures of the catalytically impaired promirolysin point mutant E225A at 1.4 and 1.6 Å revealed that latency is exerted by an N-terminal 34-residue pro-segment that shields the front surface of the 274-residue catalytic domain, thus preventing substrate access. The catalytic domain conforms to the metzincin clan of metallopeptidases and contains a double calcium site, which acts as a calcium switch for activity. The pro-segment traverses the active-site cleft in the opposite direction to the substrate, which precludes its cleavage. It is anchored to the mature enzyme through residue Arg21, which intrudes into the specificity pocket in cleft sub-site S1'. Moreover, residue Cys23 within a conserved cysteine-glycine motif blocks the catalytic zinc ion by a cysteine-switch mechanism, first described for mammalian matrix metallopeptidases. In addition, a 1.5 Å structure was obtained for a complex of mature mirolysin and a tetradecapeptide, which filled the cleft from sub-site S1' to S6'. A citrate molecule in S1 completed a product-complex mimic that unveiled the mechanism of substrate binding and cleavage by mirolysin, the catalytic domain of which was already preformed in the zymogen. These results, including a preference for cleavage before basic residues, are likely to be valid for other unicellular pappalysins derived from archaea, bacteria, cyanobacteria, algae and fungi, including archetypal ulilysin from Methanosarcina acetivorans. They may further apply, at least in part, to the multi-domain orthologues of higher organisms.

Red complex: Polymicrobial conglomerate in oral flora: A review

Oral diseases are the complex host responses composed of a broad array of inflammatory cells, and cytokines, chemokines, and mediators derived from the cells resident in the gingival tissues, as well as from the emigrating inflammatory cells. A chronic polymicrobial challenge to the local host tissues triggers this response, which under certain circumstances, and in a subset of the population, leads to the progressing soft and hard tissue destruction that characterizes periodontitis. The red complex has been proposed as a pathogenic consortium, consisting of P. gingivalis, T. denticola, and T. forsythia. This review has attempted to examine the virulence potential and determinants of these commensal opportunists.

miR-155 promotes macrophage pyroptosis induced by Porphyromonas gingivalis through regulating the NLRP3 inflammasome

OBJECTIVE

The aim of this study is to detect pyroptosis in macrophages stimulated with Porphyromonas gingivalis and elucidate the mechanism by which P. gingivalis induces pyroptosis in macrophages.

METHODS

The immortalized human monocyte cell line U937 was stimulated with P. gingivalis W83. Flow cytometry was carried out to detect pyroptosis in macrophages. The expression of miR-155 was detected by real-time PCR and inhibited using RNAi. Suppressor of cytokine signaling (SOCS) 1, cleaved GSDMD, caspase (CAS)-1, caspase-11, apoptosis-associated speck-like protein (ASC), and NOD-like receptor protein 3 (NLRP3) were detected by Western blotting, and IL-1β and IL-18 were detected by ELISA.

RESULTS

The rate of pyroptosis in macrophages and the expression of miR-155 increased upon stimulation with P. gingivalis and pyroptosis rate decreased when miR-155 was silenced. GSDMD-NT, CAS-11, CAS-1, ASC, NLRP3, IL-1β, and IL-18 levels increased, but SOCS1 decreased in U937 cells after stimulated with P. gingivalis. These changes were weakened in P. gingivalis-stimulated U937 macrophages transfected with lentiviruses carrying miR-155 shRNA compared to those transfected with non-targeting control sequence. However, there was no significant difference in ASC expression between P. gingivalis-stimulated shCont and shMiR-155 cells.

CONCLUSIONS

Porphyromonas gingivalis promotes pyroptosis in macrophages during early infection. miR-155 is involved in this process through regulating the NLRP3 inflammasome.

Peptidoglycan-type analysis of the N-acetylmuramic acid auxotrophic oral pathogen Tannerella forsythia and reclassification of the peptidoglycan-type of Porphyromonas gingivalis

BACKGROUND

Tannerella forsythia is a Gram-negative oral pathogen. Together with Porphyromonas gingivalis and Treponema denticola it constitutes the "red complex" of bacteria, which is crucially associated with periodontitis, an inflammatory disease of the tooth supporting tissues that poses a health burden worldwide. Due to the absence of common peptidoglycan biosynthesis genes, the unique bacterial cell wall sugar N-acetylmuramic acid (MurNAc) is an essential growth factor of T. forsythia to build up its peptidoglycan cell wall. Peptidoglycan is typically composed of a glycan backbone of alternating N-acetylglucosamine (GlcNAc) and MurNAc residues that terminates with anhydroMurNAc (anhMurNAc), and short peptides via which the sugar backbones are cross-linked to build up a bag-shaped network.

RESULTS

We investigated T. forsythia's peptidoglycan structure, which is an essential step towards anti-infective strategies against this pathogen. A new sensitive radioassay was developed which verified the presence of MurNAc and anhMurNAc in the cell wall of the bacterium. Upon digest of isolated peptidoglycan with endo-N-acetylmuramidase, exo-N-acetylglucosaminidase and muramyl-L-alanine amidase, respectively, peptidoglycan fragments were obtained. HPLC and mass spectrometry (MS) analyses revealed the presence of GlcNAc-MurNAc-peptides and the cross-linked dimer with retention-times and masses, respectively, equalling those of control digests of Escherichia coli and P. gingivalis peptidoglycan. Data were confirmed by tandem mass spectrometry (MS2) analysis, revealing the GlcNAc-MurNAc-tetra-tetra-MurNAc-GlcNAc dimer to contain the sequence of the amino acids alanine, glutamic acid, diaminopimelic acid (DAP) and alanine, as well as a direct cross-link between DAP on the third and alanine on the fourth position of the two opposite stem peptides. The stereochemistry of DAP was determined by reversed-phase HPLC after dabsylation of hydrolysed peptidoglycan to be of the meso-type.

CONCLUSION

T. forsythia peptidoglycan is of the A1γ-type like that of E. coli. Additionally, the classification of P. gingivalis peptidoglycan as A3γ needs to be revised to A1γ, due to the presence of meso-DAP instead of LL-DAP, as reported previously.

Effects of Sodium Tripolyphosphate on Oral Commensal and Pathogenic Bacteria

Polyphosphate (polyP) is a food additive with antimicrobial activity. Here we evaluated the effects of sodium tripolyphosphate (polyP3, Na₅P₃O₁₀) on four major oral bacterial species, in both single- and mixed-culture. PolyP3 inhibited three opportunistic pathogenic species: Fusobacterium nucleatum, Prevotella intermedia, and Porphyromonas gingivalis. On the contrary, a commensal bacterium Streptococcus gordonii was relatively less susceptible to polyP3 than the pathogens. When all bacterial species were co-cultured, polyP3 (≥ 0.09%) significantly reduced their total growth and biofilm formation, among which the three pathogenic bacteria were selectively inhibited. Collectively, polyP3 may be an alternative antibacterial agent to control oral pathogenic bacteria.

Protein glycosylation: Sweet or bitter for bacterial pathogens?

Protein glycosylation systems in many bacteria are often associated with crucial biological processes like pathogenicity, immune evasion and host-pathogen interactions, implying the significance of protein-glycan linkage. Similarly, host protein glycosylation has been implicated in antimicrobial activity as well as in promoting growth of beneficial strains. In fact, few pathogens notably modulate host glycosylation machineries to facilitate their survival. To date, diverse chemical and biological strategies have been developed for conjugate vaccine production for disease control. Bioconjugate vaccines, largely being produced by glycoengineering using PglB (the N-oligosaccharyltransferase from Campylobacter jejuni) in suitable bacterial hosts, have been highly promising with respect to their effectiveness in providing protective immunity and ease of production. Recently, a novel method of glycoconjugate vaccine production involving an O-oligosaccharyltransferase, PglL from Neisseria meningitidis, has been optimized. Nevertheless, many questions on defining antigenic determinants, glycosylation markers, species-specific differences in glycosylation machineries, etc. still remain unanswered, necessitating further exploration of the glycosylation systems of important pathogens. Hence, in this review, we will discuss the impact of bacterial protein glycosylation on its pathogenesis and the interaction of pathogens with host protein glycosylation, followed by a discussion on strategies used for bioconjugate vaccine development.

The contribution of Tannerella forsythia dipeptidyl aminopeptidase IV in the breakdown of collagen

In this study, we characterized a serine protease from Tannerella forsythia that degrades gelatin, type I, and III collagen. Tannerella forsythia is associated with periodontitis progression and severity. The primary goal of this research was to understand the mechanisms by which T. forsythia contributes to periodontitis progression. One of our previous metatranscriptomic analysis revealed that during periodontitis progression T. forsythia highly expressed the bfor_1659 ORF. The N-terminal end is homologous to dipeptidyl aminopeptidase IV (DPP IV). DPP IV is a serine protease that cleaves X-Pro or X-Ala dipeptide from the N-terminal end of proteins. Collagen type I is rich in X-Pro and X-Ala sequences, and it is the primary constituent of the periodontium. This work assessed the collagenolytic and gelatinolytic properties of BFOR_1659. To that end, the complete BFOR_1659 and its domains were purified as His-tagged recombinant proteins, and their collagenolytic activity was tested on collagen-like substrates, collagen type I and III combined, and on the extracellular matrix (ECM) formed on human gingival fibroblasts culture HGF-1. BFOR_1659 was only found in T. forsythia supernatants, highlighting its potential role on the pathogenicity of T. forsythia. We also found that BFOR_1659 efficiently degrades all tested substrates but the individual domains were inactive. Given that BFOR_1659 is highly expressed in the periodontal pocket, its clinical relevance is suggested to periodontitis progression.

Detection of Tannerella forsythia bspA and prtH genotypes among periodontitis patients and healthy subjects-A case-Control study

BACKGROUND

T. forsythia a gram negative, anaerobe inhabits the mature biofilm present at sites expressing progressive periodontitis. It is a part of "red complex" group which contributes to the pathogenesis of periodontitis. The BspA protein and prtH gene encoded cysteine protease play a vital role in the virulence of T. forsythia. The present study aims to detect the two genotypes (bspA and prtH) in periodontitis and healthy subjects.

MATERIALS & METHOD

Subgingival plaque samples were collected from periodontitis patients and healthy subjects (Chronic Periodontitis n = 128, Aggressive Periodontitis n = 72, healthy subjects n = 200). The samples were screened for the presence of T. forsythia 16S rRNA, bspA and prtH genotypes by Polymerase Chain Reaction. The prevalence of the genotypes between periodontitis patients and healthy subjects was compared with Pearson's Chi-square test. A P value of < 0.05 was considered to be statistically significant.

RESULTS

The prevalence for T. forsythia in Chronic Periodontitis (n = 128), Aggressive Periodontitis (n = 72) and health (n = 200) was 73.4%, 59.7% and 10.5% respectively. The prevalence of T.forsythia bspA/prtH genotypes was 81.90%/43.60%, 88.40%/53.50% and 33.30%/14.3% in Chronic Periodontitis, aggressive Periodontitis and health respectively. Compared to healthy subjects, the odds of detecting T.forsythia 16S rRNA was 18.53 times high in individuals with periodontitis (P = 0.0001).

CONCLUSION

The high odds ratio of T.forsythia 16S rRNA among periodontitis strongly suggests its role in periodontitis. In addition, the high prevalence of T. forsythia bspA genotype among Chronic Periodontitis signifies it as a useful marker for chronic periodontitis.

Prevalence of two Entamoeba gingivalis ST1 and ST2-kamaktli subtypes in the human oral cavity under various conditions

Advances in molecular biology have facilitated analyses of the oral microbiome; however, the parasites role is poorly understood. Periodontal disease is a multifactorial process involving complex interactions among microorganisms, the host, and environmental factors. At present, the precise composition of the mouth parasites microbiota is unclear. Two protozoan species have been detected in the oral microbiota: Trichomonas tenax and Entamoeba gingivalis, and a new variant, E. gingivalis-ST2-kamaktli, was recently identified by us. In this study, both E. gingivalis and the new E. gingivalis-ST2-kamaktli variant were detected in the oral cavities of people with healthy periodontium, individuals undergoing orthodontic treatment, and patients with periodontal disease. In the group with healthy periodontium, the prevalence of E. gingivalis-ST1 was 48.6% and that of E. gingivalis-ST2-kamaktli 29.5%, with a combined prevalence of 54.3%. In patients undergoing orthodontics treatment, 81.2% carried both amoebas, with 47.5% having E. gingivalis-ST1 and 73.8% E. gingivalis-ST2-kamaktli. In people with periodontal disease, the prevalence of E. gingivalis-ST1 was 57.8%, and that of E. gingivalis-ST2-kamaktli 50.0%, with a combined prevalence of 73.5%; hence, E. gingivalis-ST1 and E gingivalis-ST2-kamaktli were detected in all three groups. The question arises, what are E. gingivalis-ST1 and E. gingivalis-ST2-kamaktli doing in the oral cavity? Although, the answer remains unclear, our results suggest that each amoeba subtype is genetically distinct, and they exhibit different patterns of infectious behavior. We hypothesize that E. gingivalis-ST1 and E. gingivalis-ST2-kamaktli may represent separate species. Our data contribute to better understanding of the roles of E. gingivalis-ST1 and E. gingivalis-ST2-kamaktli in the oral microbiota.

Tannerella forsythia-produced methylglyoxal causes accumulation of advanced glycation endproducts to trigger cytokine secretion in human monocytes

The periodontal pathogen Tannerella forsythia has the unique ability to produce methylglyoxal (MGO), an electrophilic compound which can covalently modify amino acid side chains and generate inflammatory adducts known as advanced glycation endproducts (AGEs). In periodontitis, concentrations of MGO in gingival-crevicular fluid are increased and are correlated with the T. forsythia load. However, the source of MGO and the extent to which MGO may contribute to periodontal inflammation has not been fully explored. In this study we identified a functional homolog of the enzyme methylglyoxal synthase (MgsA) involved in the production of MGO in T. forsythia. While wild-type T.forsythia produced a significant amount of MGO in the medium, a mutant lacking this homolog produced little to no MGO. Furthermore, compared with the spent medium of the T. forsythia parental strain, the spent medium of the T. forsythia mgsA-deletion strain induced significantly lower nuclear factor-kappa B activity as well as proinflammogenic and pro-osteoclastogenic cytokines from THP-1 monocytes. The ability of T. forsythia to induce protein glycation endproducts via MGO was confirmed by an electrophoresis-based collagen chain mobility shift assay. Together these data demonstrated that T. forsythia produces MGO, which may contribute to inflammation via the generation of AGEs and thus act as a potential virulence factor of the bacterium.

N-Acetylmuramic Acid (MurNAc) Auxotrophy of the Oral Pathogen Tannerella forsythia: Characterization of a MurNAc Kinase and Analysis of Its Role in Cell Wall Metabolism

Tannerella forsythia is an anaerobic, Gram-negative oral pathogen that thrives in multispecies gingival biofilms associated with periodontitis. The bacterium is auxotrophic for the commonly essential bacterial cell wall sugar N-acetylmuramic acid (MurNAc) and, thus, strictly depends on an exogenous supply of MurNAc for growth and maintenance of cell morphology. A MurNAc transporter (Tf_MurT; Tanf_08375) and an ortholog of the Escherichia coli etherase MurQ (Tf_MurQ; Tanf_08385) converting MurNAc-6-phosphate to GlcNAc-6-phosphate were recently described for T. forsythia. In between the respective genes on the T. forsythia genome, a putative kinase gene is located. In this study, the putative kinase (Tf_MurK; Tanf_08380) was produced as a recombinant protein and biochemically characterized. Kinetic studies revealed Tf_MurK to be a 6-kinase with stringent substrate specificity for MurNAc exhibiting a 6 × 104-fold higher catalytic efficiency (kcat/Km ) for MurNAc than for N-acetylglucosamine (GlcNAc) with kcat values of 10.5 s-1 and 0.1 s-1 and Km values of 200 μM and 116 mM, respectively. The enzyme kinetic data suggest that Tf_MurK is subject to substrate inhibition (Ki[S] = 4.2 mM). To assess the role of Tf_MurK in the cell wall metabolism of T. forsythia, a kinase deletion mutant (ΔTf_murK::erm) was constructed. This mutant accumulated MurNAc intracellularly in the exponential phase, indicating the capability to take up MurNAc, but inability to catabolize MurNAc. In the stationary phase, the MurNAc level was reduced in the mutant, while the level of the peptidoglycan precursor UDP-MurNAc-pentapeptide was highly elevated. Further, according to scanning electron microscopy evidence, the ΔTf_murK::erm mutant was more tolerant toward low MurNAc concentration in the medium (below 0.5 μg/ml) before transition from healthy, rod-shaped to fusiform cells occurred, while the parent strain required > 1 μg/ml MurNAc for optimal growth. These data reveal that T. forsythia readily catabolizes exogenous MurNAc but simultaneously channels a proportion of the sugar into peptidoglycan biosynthesis. Deletion of Tf_murK blocks MurNAc catabolism and allows the direction of MurNAc solely to peptidoglycan biosynthesis, resulting in a growth advantage in MurNAc-depleted medium. This work increases our understanding of the T. forsythia cell wall metabolism and may pave new routes for lead finding in the treatment of periodontitis.

Investigation of a Novel Predictive Biomarker Profile for the Outcome of Periodontal Treatment

BACKGROUND

An ability to predict the response to conventional non-surgical treatment of a periodontal site would be advantageous. However, biomarkers or tests devised to achieve this have lacked sensitivity. The aim of this study is to assess the ability of a novel combination of biomarkers to predict treatment outcome of patients with chronic periodontitis.

METHODS

Gingival crevicular fluid (GCF) and subgingival plaque were collected from 77 patients at three representative sites, one healthy (probing depth [PD] ≤3 mm) and two diseased (PD ≥6 mm), at baseline and at 3 and 6 months after treatment. Patients received standard non-surgical periodontal treatment at each time point as appropriate. The outcome measure was improvement in probing depth of ≥2 mm. Concentrations of active enzymes (matrix metalloproteinase [MMP]-8, elastase, and sialidase) in GCF and subgingival plaque levels of Porphyromonas gingivalis, Tannerella forsythia, and Fusobacterium nucleatum were analyzed for prediction of the outcome measure.

RESULTS

Using threshold values of MMP-8 (94 ng/μL), elastase (33 ng/μL), sialidase (23 ng/μL), and levels of P. gingivalis (0.23%) and T. forsythia (0.35%), receiver operating characteristic curves analysis demonstrated that these biomarkers at baseline could differentiate healthy from diseased sites (sensitivity and specificity ≥77%). Furthermore, logistic regression showed that this combination of these biomarkers at baseline provided accurate predictions of treatment outcome (≥92%).

CONCLUSION

The "fingerprint" of GCF enzymes and bacteria described here offers a way to predict the outcome of non-surgical periodontal treatment on a site-specific basis.

A structure-derived snap-trap mechanism of a multispecific serpin from the dysbiotic human oral microbiome

Enduring host-microbiome relationships are based on adaptive strategies within a particular ecological niche. Tannerella forsythia is a dysbiotic member of the human oral microbiome that inhabits periodontal pockets and contributes to chronic periodontitis. To counteract endopeptidases from the host or microbial competitors, T. forsythia possesses a serpin-type proteinase inhibitor called miropin. Although serpins from animals, plants, and viruses have been widely studied, those from prokaryotes have received only limited attention. Here we show that miropin uses the serpin-type suicidal mechanism. We found that, similar to a snap trap, the protein transits from a metastable native form to a relaxed triggered or induced form after cleavage of a reactive-site target bond in an exposed reactive-center loop. The prey peptidase becomes covalently attached to the inhibitor, is dragged 75 Å apart, and is irreversibly inhibited. This coincides with a large conformational rearrangement of miropin, which inserts the segment upstream of the cleavage site as an extra β-strand in a central β-sheet. Standard serpins possess a single target bond and inhibit selected endopeptidases of particular specificity and class. In contrast, miropin uniquely blocked many serine and cysteine endopeptidases of disparate architecture and substrate specificity owing to several potential target bonds within the reactive-center loop and to plasticity in accommodating extra β-strands of variable length. Phylogenetic studies revealed a patchy distribution of bacterial serpins incompatible with a vertical descent model. This finding suggests that miropin was acquired from the host through horizontal gene transfer, perhaps facilitated by the long and intimate association of T. forsythia with the human gingiva.

Energy dispersive spectroscopy-scanning transmission electron microscope observations of free radical production in human polymorphonuclear leukocytes phagocytosing non-opsonized Tannerella forsythia

We investigated the association between human polymorphonuclear leukocytes (PMNs) and non-opsonized Tannerella forsythia ATCC 43037 displaying a serum-resistant surface layer (S-layer). When PMNs were mixed with T. forsythia in suspension, the cells phagocytosed T. forsythia cells. Nitro blue tetrazolium (NBT) reduction, indicative of O2- production, was observed by light microscopy; cerium (Ce) perhydroxide deposition, indicative of H₂ O₂ production, was observed by electron microscopy. We examined the relationship between high-molecular-weight proteins of the S-layer and Ce reaction (for T. forsythia phagocytosis) using electron microscopic immunolabeling. Immunogold particles were localized within the PMNs and on cell surfaces, labelling at the same Ce-reacted sites where the S-layer was present. We then used energy dispersive spectroscopy (EDS)-scanning transmission electron microscope (STEM) to perform Ce and nitrogen (N) (for S-layer immunocytochemistry) elemental analysis on the phagocytosed cells. That is, the elemental mapping and analysis of N by EDS appeared to reflect the presence of the same moieties detected by the 3,3'-diaminobenzidine-tetrahydrochloride (DAB) reaction with horseradish peroxidase (HRP)-conjugated secondary antibodies, instead of immunogold labeling. We focused on the use of EDS-STEM to visualize the presence of N resulting from the DAB reaction. In a parallel set of experiments, we used EDS-STEM to perform Ce and gold (Au; from immunogold labeling of the S-layer) elemental analysis on the same phagocytosing cells.

Regulation and Molecular Basis of Environmental Muropeptide Uptake and Utilization in Fastidious Oral Anaerobe Tannerella forsythia

Tannerella forsythia is a Gram-negative oral anaerobe associated with periodontitis. This bacterium is auxotrophic for the peptidoglycan amino sugar N-acetylmuramic (MurNAc) and likely relies on scavenging peptidoglycan fragments (muropeptides) released by cohabiting bacteria during their cell wall recycling. Many Gram-negative bacteria utilize an inner membrane permease, AmpG, to transport peptidoglycan fragments into their cytoplasm. In the T. forsythia genome, the Tanf_08365 ORF has been identified as a homolog of AmpG permease. In order to confirm the functionality of Tanf_08365, a reporter system in an Escherichia coli host was generated that could detect AmpG-dependent accumulation of cytosolic muropeptides via a muropeptide-inducible β-lactamase reporter gene. In trans complementation of this reporter strain with a Tanf_08365 containing plasmid caused significant induction of β-lactamase activity compared to that with an empty plasmid control. These data indicated that Tanf_08365 acted as a functional muropeptide permease causing accumulation of muropeptides in E. coli and thus suggested that it is a permease involved in muropeptide scavenging in T. forsythia. Furthermore, we showed that the promoter regulating the expression of Tanf_08365 was activated significantly by a hybrid two-component system regulatory protein, GppX. We also showed that compared to the parental T. forsythia strain a mutant lacking GppX in which the expression of AmpG was reduced significantly attenuated in utilizing free muropeptides. In summary, we have uncovered the mechanism by which this nutritionally fastidious microbe accesses released muropeptides in its environment, opening up the possibility of targeting this activity to reduce its numbers in periodontitis patients with potential benefits in the treatment of disease.

Draft Genome Sequence of Tannerella forsythia Clinical Isolate 9610

We present here the draft genome sequence of Tannerella forsythia 9610, a clinical isolate obtained from a periodontitis patient. The genome is composed of 79 scaffolds with 82 contigs, for a length of 3,201,941 bp and a G+C of 47.3%.

Macrophage inducible C-type lectin (Mincle) recognizes glycosylated surface (S)-layer of the periodontal pathogen Tannerella forsythia

The oral pathogen Tannerella forsythia is implicated in the development of periodontitis, a common inflammatory disease that leads to the destruction of the gum and tooth supporting tissues, often leading to tooth loss. T. forsythia is a unique Gram-negative organism endowed with an elaborate protein O-glycosylation system that allows the bacterium to express a glycosylated surface (S)-layer comprising two high molecular weight glycoproteins modified with O-linked oligosaccharides. The T. forsythia S-layer has been implicated in the modulation of cytokine responses of antigen presenting cells, such as macrophages, that play a significant role during inflammation associated with periodontitis. The macrophage-inducible C-type lectin receptor (Mincle) is an FcRγ-coupled pathogen recognition receptor that recognizes a wide variety of sugar containing ligands from fungal and bacterial pathogens. In this study, we aimed to determine if Mincle might be involved in the recognition of T. forsythia S-layer and modulation of cytokine response of macrophages against the bacterium. Binding studies using recombinant Mincle-Fc fusion protein indicated a specific Ca2+-dependent binding of Mincle to T. forsythia S-layer. Subsequent experiments with Mincle-expressing and Mincle-knockdown macrophages revealed a role for Mincle/S-layer interaction in the induction of both pro- and anti-inflammatory cytokine secretion in macrophages stimulated with T. forsythia as well as its S-layer. Together, these studies revealed Mincle as an important macrophage receptor involved in the modulation of cytokine responses of macrophages against T. forsythia, and thus may play a critical role in orchestrating the host immune response against the bacterium.

Mirolysin, a LysargiNase from Tannerella forsythia, proteolytically inactivates the human cathelicidin, LL-37

Tannerella forsythia is a periodontal pathogen expressing six secretory proteolytic enzymes with a unique multidomain structure referred to as KLIKK proteases. Two of these proteases, karilysin and mirolysin, were previously shown to protect the bacterium against complement-mediated bactericidal activity. The latter metalloprotease, however, was not characterized at the protein level. Therefore, we purified recombinant mirolysin and subjected it to detailed biochemical characterization. Mirolysin was obtained as a 66 kDa zymogen, which autoproteolytically processed itself into a 31 kDa active form via truncations at both the N- and C-termini. Further autodegradation was prevented by calcium. Substrate specificity was determined by the S1' subsite of the substrate-binding pocket, which shows strong preference for Arg and Lys at the carbonyl side of a scissile peptide bond (P1' residue). The protease cleaved an array of host proteins, including human fibronectin, fibrinogen, complement proteins C3, C4, and C5, and the antimicrobial peptide, LL-37. Degradation of LL-37 abolished not only the bactericidal activity of the peptide, but also its ability to bind lipopolysaccharide (LPS), thus quenching the endotoxin proinflammatory activity. Taken together, these results indicate that, through cleavage of LL-37 and complement proteins, mirolysin might be involved in evasion of the host immune response.

Identification of a Novel N-Acetylmuramic Acid Transporter in Tannerella forsythia

Tannerella forsythia is a Gram-negative periodontal pathogen lacking the ability to undergo de novo synthesis of amino sugars N-acetylmuramic acid (MurNAc) and N-acetylglucosamine (GlcNAc) that form the disaccharide repeating unit of the peptidoglycan backbone. T. forsythia relies on the uptake of these sugars from the environment, which is so far unexplored. Here, we identified a novel transporter system of T. forsythia involved in the uptake of MurNAc across the inner membrane and characterized a homolog of the Escherichia coli MurQ etherase involved in the conversion of MurNAc-6-phosphate (MurNAc-6-P) to GlcNAc-6-P. The genes encoding these components were identified on a three-gene cluster spanning Tanf_08375 to Tanf_08385 located downstream from a putative peptidoglycan recycling locus. We show that the three genes, Tanf_08375, Tanf_08380, and Tanf_08385, encoding a MurNAc transporter, a putative sugar kinase, and a MurQ etherase, respectively, are transcriptionally linked. Complementation of the Tanf_08375 and Tanf_08380 genes together in trans, but not individually, rescued the inability of an E. coli mutant deficient in the phosphotransferase (PTS) system-dependent MurNAc transporter MurP as well as that of a double mutant deficient in MurP and components of the PTS system to grow on MurNAc. In addition, complementation with this two-gene construct in E. coli caused depletion of MurNAc in the medium, further confirming this observation. Our results show that the products of Tanf_08375 and Tanf_08380 constitute a novel non-PTS MurNAc transporter system that seems to be widespread among bacteria of the Bacteroidetes phylum. To the best of our knowledge, this is the first identification of a PTS-independent MurNAc transporter in bacteria.

IMPORTANCE

In this study, we report the identification of a novel transporter for peptidoglycan amino sugar N-acetylmuramic acid (MurNAc) in the periodontal pathogen T. forsythia It has been known since the late 1980s that T. forsythia is a MurNAc auxotroph relying on environmental sources for this essential sugar. Most sugar transporters, and the MurNAc transporter MurP in particular, require a PTS phosphorelay to drive the uptake and concurrent phosphorylation of the sugar through the inner membrane in Gram-negative bacteria. Our study uncovered a novel type of PTS-independent MurNAc transporter, and although so far, it seems to be unique to T. forsythia, it may be present in a range of bacteria both of the oral cavity and gut, especially of the phylum Bacteroidetes.

Identification and characterization of a chymotrypsin-like serine protease from periodontal pathogen, Tannerella forsythia

Tannerella forsythia is a bacteria associated with severe periodontal disease. This study reports identification and characterization of a membrane-associated serine protease from T. forsythia. The protease was isolated from T. forsythia membrane fractions and shown to cleave both gelatin and type I collagen. The protease was able to cleave both substrates over a wide range of pH values, however optimal cleavage occurred at pH 7.5 for gelatin and 8.0 for type I collagen. The protease was also shown to cleave both gelatin and type I collagen at the average reported temperature for the gingival sulcus however it showed a lack of thermal stability with a complete loss of activity by 60 °C. When treated with protease inhibitors the enzyme's activity could only be completely inhibited by serine protease inhibitors antipain and phenylmethanesulfonyl fluoride (PMSF). Further characterization of the protease utilized serine protease synthetic peptides. The protease cleaved N-succinyl-Ala-Ala-Pro-Phe p-nitroanilide but not N_α-benzoyl-dl-arginine p-nitroanilide (BAPNA) or N-methoxysuccinyl-Ala-Ala-Pro-Val p-nitroanilide indicating that the protease is a chymotrypsin-like serine protease. Since type I collagen is a major component in the gingival tissues and periodontal ligament, identification and characterization of this enzyme provides important information regarding the role of T. forsythia in periodontal disease.

Emerging facets of prokaryotic glycosylation

Glycosylation of proteins is one of the most prevalent post-translational modifications occurring in nature, with a wide repertoire of biological implications. Pathways for the main types of this modification, the N- and O-glycosylation, can be found in all three domains of life-the Eukarya, Bacteria and Archaea-thereby following common principles, which are valid also for lipopolysaccharides, lipooligosaccharides and glycopolymers. Thus, studies on any glycoconjugate can unravel novel facets of the still incompletely understood fundamentals of protein N- and O-glycosylation. While it is estimated that more than two-thirds of all eukaryotic proteins would be glycosylated, no such estimate is available for prokaryotic glycoproteins, whose understanding is lagging behind, mainly due to the enormous variability of their glycan structures and variations in the underlying glycosylation processes. Combining glycan structural information with bioinformatic, genetic, biochemical and enzymatic data has opened up an avenue for in-depth analyses of glycosylation processes as a basis for glycoengineering endeavours. Here, the common themes of glycosylation are conceptualised for the major classes of prokaryotic (i.e. bacterial and archaeal) glycoconjugates, with a special focus on glycosylated cell-surface proteins. We describe the current knowledge of biosynthesis and importance of these glycoconjugates in selected pathogenic and beneficial microbes.

Lysine-specific proteolytic activity responsible for forsythia detaching factor modification

OBJECTIVES

The objective of the present study was to clarify the lysine-specific proteolytic activity derived from periodontal pathogens responsible for Forsythia detaching factor (FDF) modification.

DESIGN

The activity responsible for FDF modification in Tannerella forsythia and Porphyromonas gingivalis were evaluated by colorimetric assay using Ac-Arg-Ala-Lys-p-nitroaniline as a substrate. FDF modification in T. forsythia and P. gingivalis were evaluated by Western blotting using recombinant FDF (rFDF) as a substrate. Furthermore, the activity in GCF of 20 patients with periodontitis and 10 healthy subjects was also evaluated by colorimetric assay. Bacteria in subgingival plaque were detected using polymerase chain reaction.

RESULTS

The activity of both bacteria in colorimetric assay were 21.35 unit (P. gingivalis) and 3.61 unit (T. forsythia), respectively. Western blot analysis revealed that P. gingivalis was found to efficiently degrade rFDF and T. forsythia partially cleaved rFDF. The activity in GCF from patients with periodontitis (clinically healthy sites: CH, deep bleeding sites: DB and deep non-bleeding sites: DNB) was significantly higher than those from healthy subjects (healthy sites: H). Among the patients with periodontitis, the activity from CH was significantly lower than those from DB and DNB. T. forsythia was detected in 68.4% of DNB, in 78.4% of DB and in none of CH. P. gingivalis was detected in 63.2% of DNB, in 84.0% of DB and in 10.5% of CH. No bacterium was detected in healthy subjects.

CONCLUSION

The lysine-specific proteolytic activity responsible for FDF modification correlates with the presence of major periodontal pathogens.

In vitro Resistance Testing of Porphyromonas gingivalis, Prevotella intermedia, and Tannerella forsythia to Triclosan

AIM

To determine the sensitivity of Porphyromonas gingivalis, Prevotella intermedia, and Tannerella forsythia to triclosan, and determine if these bacteria develop resistance to triclosan upon prolonged exposure.

MATERIALS AND METHODS

Susceptibility to triclosan was tested against three periodontal pathogens P. gingivalis, P. intermedia, and T. forsythia. Escherichia coli strains sensitive and resistant to triclosan were used as biological controls to confirm the efficacy of triclosan in the assays. Agar plates were prepared locally with vitamin K and hemin-supplemented medium.

RESULTS

Porphyromonas gingivalis and P. intermedia did not grow on plates containing ≥ 2 μg/ml triclosan, while T. forsythia did not grow on ≥ 1.66 μg/ml. Colonies of P. intermedia resistant to triclosan developed after prolonged incubation at 2 μg/ml, but this resistance disappeared during subculture in the absence of triclosan.

CONCLUSION

No significant resistance to triclosan was detected for these species.

CLINICAL SIGNIFICANCE

Dental products containing triclosan can be beneficial in controlling periodontal disease.

Sialic acid transporter NanT participates in Tannerella forsythia biofilm formation and survival on epithelial cells

Tannerella forsythia is a periodontal pathogen implicated in periodontitis. This gram-negative pathogen depends on exogenous peptidoglycan amino sugar N-acetylmuramic acid (NAM) for growth. In the biofilm state the bacterium can utilize sialic acid (Neu5Ac) instead of NAM to sustain its growth. Thus, the sialic acid utilization system of the bacterium plays a critical role in the growth and survival of the organism in the absence of NAM. We sought the function of a T. forsythia gene annotated as nanT coding for an inner-membrane sugar transporter located on a sialic acid utilization genetic cluster. To determine the function of this putative sialic acid transporter, an isogenic nanT-deletion mutant generated by allelic replacement strategy was evaluated for biofilm formation on NAM or Neu5Ac, and survival on KB epithelial cells. Moreover, since T. forsythia forms synergistic biofilms with Fusobacterium nucleatum, co-biofilm formation activity in mixed culture and sialic acid uptake in culture were also assessed. The data showed that the nanT-inactivated mutant of T. forsythia was attenuated in its ability to uptake sialic acid. The mutant formed weaker biofilms compared to the wild-type strain in the presence of sialic acid and as co-biofilms with F. nucleatum. Moreover, compared to the wild-type T. forsythia nanT-inactivated mutant showed reduced survival when incubated on KB epithelial cells. Taken together, the data presented here demonstrate that NanT-mediated sialic transportation is essential for sialic acid utilization during biofilm growth and survival of the organism on epithelial cells and implies sialic acid might be key for its survival both in subgingival biofilms and during infection of human epithelial cells in vivo.

Pathogenic potential of Tannerella forsythia enolase

Although enolases are cytosolic enzymes involved in the glycolytic pathway, they can also be secreted or expressed on the surface of a variety of eukaryotic cells and bacteria. Surface-exposed enolases of eukaryotes and bacteria can function as plasminogen receptors. Furthermore, antibodies raised against bacterial enolases can react with host enolases, suggesting molecular mimicry between bacterial and host enzymes. In this study, we analyzed an enolase of the major periodontopathogen Tannerella forsythia, which is either secreted or present on the cell surface, via matrix-assisted laser desorption ionization time-of-flight mass spectrometry and immunofluorescence, respectively. The T. forsythia enolase retained the enzymatic activity converting 2-phosphoglycerate to phosphoenolpyruvate and showed plasminogen binding and activating ability, which resulted in the degradation of fibronectin secreted from human gingival fibroblasts. In addition, it induced proinflammatory cytokine production, including interleukin-1β (IL-1β), IL-6, IL-8, and tumour necrosis factor-α (TNF-a) in the human THP-1 monocytic cell line. Taken together, our results demonstrate that T. forsythia enolase plays a role in pathogenesis in the host by plasminogen activation and proinflammatory cytokine induction, which has the potential to exaggerate inflammation in periodontitis.

KLIKK proteases of Tannerella forsythia: putative virulence factors with a unique domain structure

Comparative genomics of virulent Tannerella forsythia ATCC 43037 and a close health-associated relative, Tannerella BU063, revealed, in the latter, the absence of an entire array of genes encoding putative secretory proteases that possess a nearly identical C-terminal domain (CTD) that ends with a -Lys-Leu-Ile-Lys-Lys motif. This observation suggests that these proteins, referred to as KLIKK proteases, may function as virulence factors. Re-sequencing of the loci of the KLIKK proteases found only six genes grouped in two clusters. All six genes were expressed by T. forsythia in routine culture conditions, although at different levels. More importantly, a transcript of each gene was detected in gingival crevicular fluid (GCF) from periodontitis sites infected with T. forsythia indicating that the proteases are expressed in vivo. In each protein, a protease domain was flanked by a unique N-terminal profragment and a C-terminal extension ending with the CTD. Partially purified recombinant proteases showed variable levels of proteolytic activity in zymography gels and toward protein substrates, including collagen, gelatin, elastin, and casein. Taken together, these results indicate that the pathogenic strain of T. forsythia secretes active proteases capable of degrading an array of host proteins, which likely represents an important pathogenic feature of this bacterium.

Bacteriophage and their potential roles in the human oral cavity

The human oral cavity provides the perfect portal of entry for viruses and bacteria in the environment to access new hosts. Hence, the oral cavity is one of the most densely populated habitats of the human body containing some 6 billion bacteria and potentially 35 times that many viruses. The role of these viral communities remains unclear; however, many are bacteriophage that may have active roles in shaping the ecology of oral bacterial communities. Other implications for the presence of such vast oral phage communities include accelerating the molecular diversity of their bacterial hosts as both host and phage mutate to gain evolutionary advantages. Additional roles include the acquisitions of new gene functions through lysogenic conversions that may provide selective advantages to host bacteria in response to antibiotics or other types of disturbances, and protection of the human host from invading pathogens by binding to and preventing pathogens from crossing oral mucosal barriers. Recent evidence suggests that phage may be more involved in periodontal diseases than were previously thought, as their compositions in the subgingival crevice in moderate to severe periodontitis are known to be significantly altered. However, it is unclear to what extent they contribute to dysbiosis or the transition of the microbial community into a state promoting oral disease. Bacteriophage communities are distinct in saliva compared to sub- and supragingival areas, suggesting that different oral biogeographic niches have unique phage ecology shaping their bacterial biota. In this review, we summarize what is known about phage communities in the oral cavity, the possible contributions of phage in shaping oral bacterial ecology, and the risks to public health oral phage may pose through their potential to spread antibiotic resistance gene functions to close contacts.

Point-of-care detection of Tannerella forsythia using an antigen-antibody assisted dielectrophoretic impedance measurement method

The importance of periodontal treatment planning based on diagnosis with clinical detection of periodontal pathogens has been well recognized. However, reliable detection and quantification methods that can be conveniently used at chair-side have yet to be developed. This study aimed to evaluate the clinical use of a novel apparatus which uses an antigen-antibody reaction assisted dielectrophoretic impedance measurement (AA-DEPIM) for the detection of a prominent periodontal pathogen, Tannerella forsythia. A total of 15 patients with a clinical diagnosis of chronic periodontitis, three periodontally healthy volunteers and two with gingivitis were subjected to clinical and microbiological examinations. Saliva samples were analyzed for the presence of T. forsythia using AA-DEPIM, PCR-Invader and real-time PCR methods. The measurement values for total bacteria and T. forsythia using the prototype AA-DEPIM apparatus were significantly greater in periodontitis group than those in healthy/gingivitis group. Using the AA-DEPIM apparatus with tentative cut-off values, T. forsythia was detected for 14 (12 with periodontitis and 2 either healthy or with gingivitis) out of 20 individuals. The measurement for the detection of T. forsythia by the AA-DEPIM method showed a significant positive correlation with the detection by PCR-Invader (r = 0.541, p = 0.01) and the real-time PCR method (r = 0.834, p = 0.01). When the PCR-Invader method was used as a reference, the sensitivity and specificity of the AA-DEPIM method were 76.5% and 100%, respectively. The results suggested that the AA-DEPIM method has potential to be used for clinically evaluating salivary presence of T. forsythia at chair-side.

TRIAL REGISTRATION

UMIN Clinical Trials Registry (UMIN-CTR) UMIN000012181.

A pathogenic trace of Tannerella forsythia - shedding of soluble fully active tumor necrosis factor α from the macrophage surface by karilysin

Tannerella forsythia is implicated as a pathogen causing chronic and aggressive periodontitis. However, its virulence factors, including numerous putative proteases, are mostly uncharacterized. Karilysin is a newly described matrix metalloprotease-like enzyme of T. forsythia. Since pathogen-derived proteases may affect the host defense system via modulation of the cytokine network, the aim of this study was to determine the influence of karilysin on tumor necrosis factor-α (TNF-α). The results showed that karilysin cleaved the membrane form of TNF-α on the surface of macrophages, and that this led to an increased concentration of soluble TNF-α in the conditioned medium. Importantly, despite partial degradation of soluble TNF-α by karilysin, the released cytokine retained its biological activity, inducing apoptosis and stimulating autocrine pathway of pro-inflammatory gene expression. Notably, the observed effect required proteolytic activity by karilysin, since a catalytically inactive mutant of the enzyme did not affect TNF-α secretion. The shedding was independent of the activity of ADAM17, a major endogenous TNF-α converting enzyme. Karilysin-dependent TNF-α release from the cell surface is likely to occur in vivo because human plasma, the main constituent of gingival crevicular fluid, only slightly affected the sheddase activity of karilysin. Taken together, these results indicate that karilysin modulates the host immune response through regulation of TNF-α secretion, and should therefore be considered as a new virulence factor of T. forsythia.

Genetic characteristics and pathogenic mechanisms of periodontal pathogens

Periodontal disease is caused by a group of bacteria that utilize a variety of strategies and molecular mechanisms to evade or overcome host defenses. Recent research has uncovered new evidence illuminating interesting aspects of the virulence of these bacteria and their genomic variability. This paper summarizes some of the strategies utilized by the major species - Aggregatibacter actinomycetemcomitans, Tannerella forsythia, Treponema denticola, and Porphyromonas gingivalis - implicated in the pathogenesis of periodontal disease. Whole-genome sequencing of 14 diverse A. actinomycetemcomitans strains has revealed variations in their genetic content (ranging between 0.4% and 19.5%) and organization. Strikingly, isolates from human periodontal sites showed no genomic changes during persistent colonization. T. forsythia manipulates the cytokine responses of macrophages and monocytes through its surface glycosylation. Studies have revealed that bacterial surface-expressed O-linked glycans modulate T-cell responses during periodontal inflammation. Periodontal pathogens belonging to the "red complex" consortium express neuraminidases, which enables them to scavenge sialic acid from host glycoconjugates. Analysis of recent data has demonstrated that the cleaved sialic acid acts as an important nutrient for bacterial growth and a molecule for the decoration of bacteria surfaces to help evade the host immune attack. In addition, bacterial entry into host cells is also an important prerequisite for the lifestyle of periodontal pathogens such as P. gingivalis. Studies have shown that, after its entry into the cell, this bacterium uses multiple sorting pathways destined for autophagy, lysosomes, or recycling pathways. In addition, P. gingivalis releases outer membrane vesicles which enter cells via endocytosis and cause cellular functional impairment.

Pathogens and host immunity in the ancient human oral cavity

Calcified dental plaque (dental calculus) preserves for millennia and entraps biomolecules from all domains of life and viruses. We report the first, to our knowledge, high-resolution taxonomic and protein functional characterization of the ancient oral microbiome and demonstrate that the oral cavity has long served as a reservoir for bacteria implicated in both local and systemic disease. We characterize (i) the ancient oral microbiome in a diseased state, (ii) 40 opportunistic pathogens, (iii) ancient human-associated putative antibiotic resistance genes, (iv) a genome reconstruction of the periodontal pathogen Tannerella forsythia, (v) 239 bacterial and 43 human proteins, allowing confirmation of a long-term association between host immune factors, 'red complex' pathogens and periodontal disease, and (vi) DNA sequences matching dietary sources. Directly datable and nearly ubiquitous, dental calculus permits the simultaneous investigation of pathogen activity, host immunity and diet, thereby extending direct investigation of common diseases into the human evolutionary past.

Periodontal disease associated with red complex bacteria in dogs

OBJECTIVE

Red complex bacteria (Treponema denticola, Tannerella forsythia and Porphyromonas gingivalis) play a major role in the aetiology of periodontal disease in humans. This study was designed to evaluate the association of such bacteria with periodontal disease in dogs.

METHODS

Seventy-three subgingival samples taken from dogs ranging from 2 months to 12 years (median age 4 years) were tested for red complex bacteria using a polymerase chain reaction assay.

RESULTS

Thirty-six of 73 (49 · 3%) dogs were found to be positive for T. forsythia and P. gingivalis. Dogs with gingivitis or periodontitis were more likely to be infected with T. forsythia and P. gingivalis [odds ratio (OR) 5 · 4 (confidence interval (CI) 1 · 9-15 · 6), P = 0 · 002] than healthy animals. Only 3 (4 · 1%) of 73 samples were positive for red complex bacteria, but the association with periodontal disease was not significant.

CONCLUSION AND CLINICAL RELEVANCE

The results indicate that involvement of red complex bacteria in periodontal disease in dogs is similar to that observed in humans. Only the concurrent presence of T. forsythia and P. gingivalis were correlated to periodontal disease in dogs in this study.