Viscosity-dependent locomotion of oral spirochetes

The Mechanistic Pathways of Periodontal Pathogens Entering the Brain: The Potential Role of Treponema denticola in Tracing Alzheimer’s Disease Pathology

Alzheimer’s Disease (AD) is a complex neurodegenerative disease and remains the most common form of dementia. The pathological features include amyloid (Aβ) accumulation, neurofibrillary tangles (NFTs), neural and synaptic loss, microglial cell activation, and an increased blood–brain barrier permeability. One longstanding hypothesis suggests that a microbial etiology is key to AD initiation. Among the various periodontal microorganisms, Porphyromonas gingivalis has been considered the keystone agent to potentially correlate with AD, due to its influence on systemic inflammation. P. gingivalis together with Treponema denticola and Tannerella forsythia belong to the red complex consortium of bacteria advocated to sustain periodontitis within a local dysbiosis and a host response alteration. Since the implication of P. gingivalis in the pathogenesis of AD, evidence has emerged of T. denticola clusters in some AD brain tissue sections. This narrative review explored the potential mode of spirochetes entry into the AD brain for tracing pathology. Spirochetes are slow-growing bacteria, which can hide within ganglia for many years. It is this feature in combination with the ability of these bacteria to evade the hosts’ immune responses that may account for a long lag phase between infection and plausible AD disease symptoms. As the locus coeruleus has direct connection between the trigeminal nuclei to periodontal free nerve endings and proprioceptors with the central nervous system, it is plausible that they could initiate AD pathology from this anatomical region.

The bank of swimming organisms at the micron scale (BOSO-Micro)

Unicellular microscopic organisms living in aqueous environments outnumber all other creatures on Earth. A large proportion of them are able to self-propel in fluids with a vast diversity of swimming gaits and motility patterns. In this paper we present a biophysical survey of the available experimental data produced to date on the characteristics of motile behaviour in unicellular microswimmers. We assemble from the available literature empirical data on the motility of four broad categories of organisms: bacteria (and archaea), flagellated eukaryotes, spermatozoa and ciliates. Whenever possible, we gather the following biological, morphological, kinematic and dynamical parameters: species, geometry and size of the organisms, swimming speeds, actuation frequencies, actuation amplitudes, number of flagella and properties of the surrounding fluid. We then organise the data using the established fluid mechanics principles for propulsion at low Reynolds number. Specifically, we use theoretical biophysical models for the locomotion of cells within the same taxonomic groups of organisms as a means of rationalising the raw material we have assembled, while demonstrating the variability for organisms of different species within the same group. The material gathered in our work is an attempt to summarise the available experimental data in the field, providing a convenient and practical reference point for future studies.

Propulsive nanomachines: the convergent evolution of archaella, flagella and cilia

Echoing the repeated convergent evolution of flight and vision in large eukaryotes, propulsive swimming motility has evolved independently in microbes in each of the three domains of life. Filamentous appendages – archaella in Archaea, flagella in Bacteria and cilia in Eukaryotes – wave, whip or rotate to propel microbes, overcoming diffusion and enabling colonization of new environments. The implementations of the three propulsive nanomachines are distinct, however: archaella and flagella rotate, while cilia beat or wave; flagella and cilia assemble at their tips, while archaella assemble at their base; archaella and cilia use ATP for motility, while flagella use ion-motive force. These underlying differences reflect the tinkering required to evolve a molecular machine, in which pre-existing machines in the appropriate contexts were iteratively co-opted for new functions and whose origins are reflected in their resultant mechanisms. Contemporary homologies suggest that archaella evolved from a non-rotary pilus, flagella from a non-rotary appendage or secretion system, and cilia from a passive sensory structure. Here, we review the structure, assembly, mechanism and homologies of the three distinct solutions as a foundation to better understand how propulsive nanomachines evolved three times independently and to highlight principles of molecular evolution.

The Role of Treponema denticola Motility in Synergistic Biofilm Formation With Porphyromonas gingivalis

Chronic periodontitis has a polymicrobial biofilm etiology and interactions between key oral bacterial species, such as Porphyromonas gingivalis and Treponema denticola contribute to disease progression. P. gingivalis and T. denticola are co-localized in subgingival plaque and have been previously shown to exhibit strong synergy in growth, biofilm formation and virulence in an animal model of disease. The motility of T. denticola, although not considered as a classic virulence factor, may be involved in synergistic biofilm development between P. gingivalis and T. denticola. We determined the role of T. denticola motility in polymicrobial biofilm development using an optimized transformation protocol to produce two T. denticola mutants targeting the motility machinery. These deletion mutants were non-motile and lacked the gene encoding the flagellar hook protein of the periplasmic flagella (ΔflgE) or a component of the stator motor that drives the flagella (ΔmotB). The specificity of these gene deletions was determined by whole genome sequencing. Quantitative proteomic analyses of mutant strains revealed that the specific inactivation of the motility-associated gene, motB, had effects beyond motility. There were 64 and 326 proteins that changed in abundance in the ΔflgE and ΔmotB mutants, respectively. In the ΔflgE mutant, motility-associated proteins showed the most significant change in abundance confirming the phenotype change for the mutant was related to motility. However, the inactivation of motB as well as stopping motility also upregulated cellular stress responses in the mutant indicating pleiotropic effects of the mutation. T. denticola wild-type and P. gingivalis displayed synergistic biofilm development with a 2-fold higher biomass of the dual-species biofilms than the sum of the monospecies biofilms. Inactivation of T. denticola flgE and motB reduced this synergy. A 5-fold reduction in dual-species biofilm biomass was found with the motility-specific ΔflgE mutant suggesting that T. denticola periplasmic flagella are essential in synergistic biofilm formation with P. gingivalis.

Comparative analysis of motility and other properties of Treponema denticola strains

The periodontitis-associated pathogen Treponema denticola is a spirochetal bacterium that swims by rotating its cell body like a corkscrew using periplasmic flagella. We compared physiologic and pathogenic properties, including motility, in four strains of T. denticola. Phase-contrast microscopy showed differential motility between the strains; ATCC 35404 showed the highest motility, followed by ATCC 33521, and the remaining two strains (ATCC 35405 and ATCC 33520) showed the lowest motility. Transmission electron microscopy showed that the low motility strains exhibited extracellular flagellar protrusions resulting from elongated flagella. Treponemal flagellar filaments are composed of three flagellins of FlaB1, FlaB2 and FlaB3. FlaB1 expression was comparable between the strains, whereas FlaB2 expression was lowest in ATCC 35404. FlaB3 expression varied among strains, with ATCC 35405, ATCC 33520, ATCC 33521, and ATCC 35404 showing the highest to lowest expression levels, respectively. Additionally, the low motility strains showed faster electrophoretic mobility of FlaB3, suggesting that posttranslational modifications of these proteins may have varied, because the amino acid sequences of FlaB3 were identical between the strains. These results suggest that inappropriate expression of FlaB2 and FlaB3 caused the unusual elongation of flagella that resulted in decreased motility. Furthermore, the low motility strains grew to higher bacterial density, and showed greater chymotrypsin-like protease activity, and more bacterial cells associated with gingival epithelial cells in comparison with the high motility strains. There may be a relationship between motility and these properties, but the genetic factors underlying this association remain unclear.

Borrelia burgdorferi CheD Promotes Various Functions in Chemotaxis and the Pathogenic Life Cycle of the Spirochete

Borrelia burgdorferi possesses a sophisticated chemotaxis signaling system; however, the roles of the majority of the chemotaxis proteins in the infectious life cycle have not yet been demonstrated. Specifically, the role of CheD during host colonization has not been demonstrated in any bacterium. Here, we systematically characterized the B. burgdorferi CheD homolog using genetics and biochemical and mouse-tick-mouse infection cycle studies. Bacillus subtilis CheD plays an important role in chemotaxis by deamidation of methyl-accepting chemotaxis protein receptors (MCPs) and by increasing the receptor kinase activity or enhancing CheC phosphatase activity, thereby regulating the levels of the CheY response regulator. Our biochemical analysis indicates that B. burgdorferi CheD significantly enhances CheX phosphatase activity by specifically interacting with the phosphatase. Moreover, CheD specifically binds two of the six MCPs, indicating that CheD may also modulate the receptor proteins. Although the motility of the cheD mutant cells was indistinguishable from that of the wild-type cells, the mutant did exhibit reduced chemotaxis. Importantly, the mutant showed significantly reduced infectivity in C3H/HeN mice via needle inoculation. Mouse-tick-mouse infection assays indicated that CheD is dispensable for acquisition or transmission of spirochetes; however, the viability of cheD mutants in ticks is marginally reduced compared to that of the wild-type or complemented cheD spirochetes. These data suggest that CheD plays an important role in the chemotaxis and pathogenesis of B. burgdorferi We propose potential connections between CheD, CheX, and MCPs and discuss how these interactions play critical roles during the infectious life cycle of the spirochete.

Porphyromonas gingivalis and Treponema denticola synergistic polymicrobial biofilm development

Chronic periodontitis has a polymicrobial biofilm aetiology and interactions between key bacterial species are strongly implicated as contributing to disease progression. Porphyromonas gingivalis, Treponema denticola and Tannerella forsythia have all been implicated as playing roles in disease progression. P. gingivalis cell-surface-located protease/adhesins, the gingipains, have been suggested to be involved in its interactions with several other bacterial species. The aims of this study were to determine polymicrobial biofilm formation by P. gingivalis, T. denticola and T. forsythia, as well as the role of P. gingivalis gingipains in biofilm formation by using a gingipain null triple mutant. To determine homotypic and polymicrobial biofilm formation a flow cell system was employed and the biofilms imaged and quantified by fluorescent in situ hybridization using DNA species-specific probes and confocal scanning laser microscopy imaging. Of the three species, only P. gingivalis and T. denticola formed mature, homotypic biofilms, and a strong synergy was observed between P. gingivalis and T. denticola in polymicrobial biofilm formation. This synergy was demonstrated by significant increases in biovolume, average biofilm thickness and maximum biofilm thickness of both species. In addition there was a morphological change of T. denticola in polymicrobial biofilms when compared with homotypic biofilms, suggesting reduced motility in homotypic biofilms. P. gingivalis gingipains were shown to play an essential role in synergistic polymicrobial biofilm formation with T. denticola.

Enhanced low-Reynolds-number propulsion in heterogeneous viscous environments

It has been known for some time that some microorganisms can swim faster in high-viscosity gel-forming polymer solutions. These gel-like media come to mimic highly viscous heterogeneous environment that these microorganisms encounter in-vivo. The qualitative explanation of this phenomena first offered by Berg and Turner [Nature (London) 278, 349 (1979)], suggests that propulsion enhancement is a result of flagellum pushing on quasi-rigid loose polymer network formed in some polymer solutions. Inspired by these observations, inertia-less propulsion in a heterogeneous viscous medium composed of sparse array of stationary obstacles embedded into a incompressible Newtonian liquid is considered. It is demonstrated that for prescribed propulsion gaits, including propagating surface distortions and rotating helical filament, the propulsion speed is enhanced when compared to swimming in purely viscous solvent. It is also shown that the locomotion in heterogenous viscous media is characterized by improved hydrodynamic efficiency. The results of the rigorous numerical simulation of the rotating helical filament propelled through a random sparse array of stationary obstructions are in close agreement with predictions of the proposed resistive force theory based on effective media approximation.

Major proteins and antigens of Treponema denticola

Treponema denticola is a Gram-negative, motile, asaccharolytic, anaerobic spirochaete which along with Porphyromonas gingivalis and Tannerella forsythia has been shown to form a bacterial consortium called the Red Complex that is strongly associated with the clinical progression of chronic periodontitis. T. denticola was grown in continuous culture in a complex medium with a mean generation time of 15.75 h. Samples from two different membrane-enriched preparations and a cytoplasm-enriched preparation were separated by two-dimensional gel electrophoresis and the proteins identified by MALDI-TOF/TOF mass spectrometry. In total, 219 non-redundant proteins were identified including numerous virulence factors, lipoproteins, ABC transporter proteins and enzymes involved in the metabolism of nine different amino acids of which glycine seems to be of particular importance. Novel findings include the identification of several abundant peptide uptake systems, and the identification of three flagellar filament outer layer proteins. Two-dimensional Western blot analysis using sera from mice immunized with formalin-killed T. denticola cells suggested that Msp, PrcA, OppA, OppA10, MglB, TmpC and several flagellar filament proteins are antigenic.

Effect of glucose on Treponema denticola cell behavior

INTRODUCTION

Treponema denticola inhabits the oral subgingival environment and is part of a proteolytic benzoyl-dl-arginine-naphthylamide-positive 'red complex' associated with active periodontal disease. Spirochetes have a unique form of chemotactic motility that may contribute to their virulence. Chemotaxis is essential for efficient nutrient-directed translocation.

METHODS

We examined the effect of glucose on T. denticola cell velocity, expression of periplasmic flagella proteins, and chemotaxis, e.g. translocation into capillary tubes.

RESULTS

The presence of glucose did not significantly effect T. denticola cell velocity in high viscosity conditions nor did it alter periplasmic flagella protein expression. The addition of glucose to capillary tubes resulted in greater numbers of T. denticola cells in tubes containing glucose. A non-motile mutant did not migrate into capillary tubes containing glucose.

CONCLUSION

These results are consistent with a chemotactic response to glucose that is motility dependent.

The flagellar cytoskeleton of the spirochetes

The recent discoveries of prokaryotic homologs of all three major eukaryotic cytoskeletal proteins (actin, tubulin, intermediate filaments) have spurred a resurgence of activity in the field of bacterial morphology. In spirochetes, however, it has long been known that the flagellar filaments act as a cytoskeletal protein structure, contributing to their shape and conferring motility on this unique phylum of bacteria. Therefore, revisiting the spirochete cytoskeleton may lead to new paradigms for exploring general features of prokaryotic morphology. This review discusses the role that the periplasmic flagella in spirochetes play in maintaining shape and producing motility. We focus on four species of spirochetes: Borrelia burgdorferi, Treponema denticola, Treponema phagedenis and Leptonema (formerly Leptospira) illini. In spirochetes, the flagella reside in the periplasmic space. Rotation of the flagella in the above species by a flagellar motor induces changes in the cell morphology that drives motility. Mutants that do not produce flagella have a markedly different shape than wild-type cells.

Prostaglandin E2Is a Main Mediator in Receptor Activator of Nuclear Factor-κB Ligand-Dependent Osteoclastogenesis Induced byPorphyromonas gingivalis, Treponema denticola, andTreponema socranskii

BACKGROUND

Periodontitis is an inflammatory disease that often leads to destruction of alveolar bone; a number of bacteria in subgingival plaque are associated with bone destruction in periodontitis. To understand the mechanism of how periodontopathogens induce osteoclastogenesis, we determined which mediators are involved in the osteoclastogenesis.

METHODS

We investigated effects of sonicates from three periodontopathic bacteria, Porphyromonas gingivalis, Treponema denticola, and Treponema socranskii, on osteoclast formation in a co-culture system of mouse calvaria-derived osteoblasts and bone marrow cells. The osteoclast formation was determined by tartrate resistant acid phosphatase (TRAP) staining. The expression of the receptor activator of nuclear factor-kappa B ligand (RANKL), prostaglandin E(2) (PGE(2)) and osteoprotegerin (OPG) in mouse calvaria-derived osteoblasts was determined by immunoassay.

RESULTS

Each bacterial sonicate induced the osteoclast formation in the co-culture system. These bacterial sonicates increased the expression of RANKL and PGE(2), and decreased the expression of OPG in osteoblasts. The addition of OPG, an inhibitor of RANKL, in the co-culture completely suppressed the osteoclastogenesis that was stimulated by each bacterial sonicate. Indomethacin, which is an inhibitor of PGE(2) synthesis, reduced more than 88% of the osteoclast formation induced by each bacterial sonicate. Indomethacin inhibited more than 80% of RANKL expression in osteoblasts induced by T. denticola and T. socranskii, and 59% by P. gingivalis. Indomethacin completely recovered the depression of OPG expression in osteoblasts by T. denticola and T. socranskii to the level of the untreated osteoblasts. Indomethacin recovered the reduction of OPG expression by P. gingivalis to 67%.

CONCLUSION

These findings suggest that the osteoclastogenesis by P. gingivalis, T. denticola, and T. socranskii is mediated by a RANKL-dependent pathway and that PGE(2) is a main factor in the pathway by the enhancing of RANKL expression and the depression of osteoprotegerin, a RANKL inhibitor.

Treponema species associated with abscesses of endodontic origin

Spirochetes have been frequently observed in abscesses of endodontic origin, but they have rarely been identified. This study sought to investigate the prevalence of eight oral treponemes in acute periradicular abscesses using a species-specific nested polymerase chain reaction assay. Purulent exudate was collected by aspiration from 19 cases diagnosed as acute periradicular abscesses and DNA extracted from the samples was initially amplified using universal 16S rDNA primers. A second round of amplification used the first polymerase chain reaction products to detect a specific fragment of the 16S rDNA of each Treponema species. The species-specific nPCR assay used in this study allowed the detection of Treponema denticola in 79%(15 of 19), Treponema socranskii in 26%(5 of 19), Treponema pectinovorum in 21% (4 of 19), Treponema amylovorum in 16% (3 of 19), and Treponema medium in 5% (1 of 19) of the cases. Spirochetal DNA was found in 89% of the cases (17 of 19). The number of Treponema species per case ranged from 1 to 3 (mean, 1.5). Treponema vincentii, Treponema lecithinolyticum and Treponema maltophilum were not detected in any pus sample. The present data lend support to the assertion that Treponema species, particularly T. denticola and T. socranskii, may be involved in the pathogenesis of acute periradicular abscesses.

Development of a novel chloramphenicol resistance expression plasmid used for genetic complementation of a fliG deletion mutant in Treponema denticola

A new expression plasmid containing the fla operon promoter and a staphylococcal chloramphenicol resistance gene, was constructed to help assess the role of fliG in Treponema denticola motility. Deletion of fliG resulted in a nonmotile mutant with a markedly decreased number of flagellar filaments. Wild-type fliG genes from T. denticola and from Treponema pallidum were cloned into this expression plasmid. In both cases, the gene restored the ability of the mutant to gyrate its cell ends and enabled colony spreading in agarose. This shuttle plasmid enables high-level expression of genes in T. denticola and possesses an efficient selectable marker that provides a new tool for treponemal genetics.

Genetic analysis of Treponema denticola ATCC 35405 biofilm formation

Treponema denticola is a major aetiological organism implicated in periodontal disease. The interaction of T. denticola with other oral bacteria, in particular Porphyromonas gingivalis, in biofilm formation is thought to be an important step in the onset of periodontal disease. The interaction between T. denticola and P. gingivalis has been examined using a panel of T. denticola mutants and their effects on mixed biofilm formation tested in a static biofilm model. T. denticola ATCC 35405 did not form detectable biofilms on various inert surfaces. However, the spirochaete was demonstrated to form a biofilm with preattached P. gingivalis 381. T. denticola cfpA, which lacks the cytoplasmic filament, was unable to produce a mixed biofilm with P. gingivalis. A T. denticola flgE mutant which lacks the flagella hook protein and is therefore non-motile displayed a reduced, but readily detectable, ability to form a mixed biofilm as did the T. denticola mutant which does not possess the major outer sheath protein (Msp). The T. denticola lrrA mutant was only moderately defective in forming mixed biofilms with P. gingivalis. However, the T. denticola methyl-accepting chemotaxis protein (DmcA) did not appear to play a major role in mixed biofilm formation. In contrast, T. denticola lacking the PrtP protein for prolyl-phenylalanine-specific protease, showed an increased ability to form mixed biofilms and a prolonged viability in the biofilm.

Chemotaxis-guided movements in bacteria

Motile bacteria often use sophisticated chemotaxis signaling systems to direct their movements. In general, bacterial chemotactic signal transduction pathways have three basic elements: (1) signal reception by bacterial chemoreceptors located on the membrane; (2) signal transduction to relay the signals from membrane receptors to the motor; and (3) signal adaptation to desensitize the initial signal input. The chemotaxis proteins involved in these signal transduction pathways have been identified and extensively studied, especially in the enterobacteria Escherichia coli and Salmonella enterica serovar typhimurium. Chemotaxis-guided bacterial movements enable bacteria to adapt better to their natural habitats via moving toward favorable conditions and away from hostile surroundings. A variety of oral microbes exhibits motility and chemotaxis, behaviors that may play important roles in bacterial survival and pathogenesis in the oral cavity.

The Periplasmic Flagellum of Spirochetes

Although spirochete periplasmic flagella have many features similar to typical bacterial flagella, they are unique in their structure and internal periplasmic location. This location provides advantages for pathogenic spirochetes to enter and to adapt in the appropriate host, and to penetrate through matrices that inhibit the motility of most other bacteria. These flagella are complex, and they dynamically interact with the spirochete cell cylinder in novel ways. Electron microscopy, tomography and three-dimensional reconstructions have provided new insights into flagellar structure and its relationship to the spirochetal cell cylinder. Recent advances in genetic methods have begun to shed light on the composition of the spirochete flagellum, and on the regulation of its synthesis. Because spirochetes have a high length to width ratio, their cells provide an opportunity to study two important features. These include the polarity or distribution of flagellar synthesis as well as the mechanisms required for coordination of the movement of the cell ends, to enable it to move in the forward or reverse direction.

PCR-based identification of Treponema maltophilum, T amylovorum, T medium, and T lecithinolyticum in primary root canal infections

OBJECTIVE

Molecular genetic methods have significantly contributed to the knowledge about the microbiota associated with infected root canals. Albeit spirochetes have been commonly observed in primary root canal infections, only recently they have been identified. The purpose of the present study was to investigate the occurrence of four treponemes-Treponema maltophilum, Treponema lecithinolyticum, Treponema amylovorum, and Treponema medium-in cases of primary endodontic infections associated with different forms of periradicular diseases through a 16S rDNA-based nested PCR assay.

DESIGN

Samples were taken from thirty-one infected root canals associated with either asymptomatic or symptomatic apical periodontitis. DNA extracted from the samples was initially amplified using universal 16S rDNA primers, followed by a second round of amplification using the first PCR products to detect a specific fragment of the 16S rDNA of each target Treponema species.

RESULTS

All cases were positive for the universal bacterial primers, indicating that samples contained bacterial DNA. Of the four target species, T. maltophilum was the most prevalent, being detected in 39% of the cases (33% of the asymptomatic cases and 50% of the symptomatic cases). T. lecithinolyticum was the next more prevalent among the species tested, being found in 26% of the samples (33% of asymptomatic cases and 10% of the symptomatic cases). T. amylovorum was found in 7% of the cases (5% of the asymptomatic cases and 10% of the symptomatic cases), while T. medium was in 13% of the cases (14% of the asymptomatic cases and 10% of the symptomatic cases). None of the species tested was significantly associated with clinical symptoms.

CONCLUSIONS

This was possibly the hitherto first study to report the occurrence of T. lecithinolyticum, T. amylovorum, and T. medium in infections of endodontic origin. Overall, findings suggested that these oral treponemes, particularly T. maltophilum and T. lecithinolyticum, can be involved in the pathogenesis of periradicular diseases.

Treponema socranskii in primary endodontic infections as detected by nested PCR

Spirochetes have been frequently observed in root canal infections, but they were rarely identified. The purpose of this study was to investigate the prevalence of Treponema socranskii in primary endodontic infections using a species-specific nested polymerase chain reaction assay. Samples were collected from 60 teeth having carious lesions, necrotic pulps, and different forms of periradicular diseases. DNA extracted from the samples was initially amplified using universal 16S rDNA primers. A second round of amplification used the first polymerase chain reaction products to detect a specific fragment of T. socranskii 16S rDNA. T. socranskii was detected in 11 of 28 asymptomatic cases (39.3%), five of 12 root canals associated with acute apical periodontitis (41.7%), and five of 20 cases diagnosed as acute periradicular abscesses (25%). There was no relationship between the presence of T. socranskii and the occurrence of symptoms. In general, this spirochete was detected in 21 of 60 samples of endodontic infections (35%). Findings suggest that T. socranskii can be involved in the pathogenesis of different forms of periradicular lesions.

Oral treponemes in primary root canal infections as detected by nested PCR

AIM

To investigate the prevalences of four Treponema species in primary root canal infections using a nested PCR assay.

METHODOLOGY

Samples were obtained from 32 infected root canals. Twenty-two cases showed chronic asymptomatic periradicular lesions and 10 symptomatic cases were diagnosed as acute apical periodontitis. DNA extracted from the samples was initially amplified using universal 16S rDNA primers. A second round of amplification used the first PCR products to detect a specific fragment of the 16S rDNA of each Treponema denticola, T. socranskii, T. vincentii and T. pectinovorum.

RESULTS

Bacteria were present in all cases sampled. T. denticola was detected in 77.3% of the asymptomatic cases, T. socranskii in 40.9%, T. vincentii in 18.2% and T. pectinovorum in 13.6%. In the cases diagnosed as acute apical periodontitis, T. denticola was detected in 80%, whilst T. socranskii and T. vincentii were detected in 40% and 10% of cases, respectively. No symptomatic case yielded T. pectinovorum. In general, nested PCR detected T. denticola in 78.1% of the cases, T. socranskii in 40.6%, T. vincentii in 15.6% and T. pectinovorum in 9.4%. At least one of the four Treponema species was found in 84.4% of the cases examined.

CONCLUSIONS

The species T. denticola was detected in a large number of the cases examined: the prevalence of T. socranskii was also relatively high. The species T. vincentii and T. pectinovorum were also found, but in a smaller number of cases. Based on these data, the recognized pathogenicity of these microorganisms and their involvement with other oral diseases, they should be included in the restricted set of putative endodontic pathogens.

Cytoplasmic filament-deficient mutant of Treponema denticola has pleiotropic defects

In Treponema denticola, a ribbon-like structure of cytoplasmic filaments spans the cytoplasm at all stages of the cell division process. Insertional inactivation was used as a first step to determine the function of the cytoplasmic filaments. A suicide plasmid was constructed that contained part of cfpA and a nonpolar erythromycin resistance cassette (ermF and ermAM) inserted near the beginning of the gene. The plasmid was electroporated into T. denticola, and double-crossover recombinants which had the chromosomal copy of cfpA insertionally inactivated were selected. Immunoblotting and electron microscopy confirmed the lack of cytoplasmic filaments. The mutant was further analyzed by dark-field microscopy to determine cell morphology and by the binding of two fluorescent dyes to DNA to assess the distribution of cellular nucleic acids. The cytoplasmic filament protein-deficient mutant exhibited pleiotropic defects, including highly condensed chromosomal DNA, compared to the homogeneous distribution of the DNA throughout the cytoplasm in a wild-type cell. Moreover, chains of cells are formed by the cytoplasmic filament-deficient mutant, and those cells show reduced spreading in agarose, which may be due to the abnormal cell length. The chains of cells and the highly condensed chromosomal DNA suggest that the cytoplasmic filaments may be involved in chromosome structure, segregation, or the cell division process in Treponema.

A flagellar gene cluster from the oral spirochaete Treponema maltophilum

A flagellar gene cluster from the oral spirochaete Treponema maltophilum ATCC 51939T was cloned. Sequence analysis revealed six putative ORFs, two of which encode the flagellar subunit proteins FlaB2 (286 aa) and FlaB3 (285 aa). Northern blot analysis revealed two flagellin transcripts with the expected size of monocistronic mRNAs. Sequence analysis and primer extension experiments indicated that the transcription of the flaB2 gene is directed by a sigma28-like FliA factor. Using fliA and fliA+ Escherichia coli K-12 strains, it was shown that flaB2 expression in E. coli required the sigma28 factor using an initiation site identical to that in Treponema maltophilum. Primer extension analysis revealed two transcriptional start sites 5' of the flaB3 gene, a strong promoter with a sigma28-like -10 promoter element and a weak promoter with a putative sigma54 promoter consensus sequence. Downstream of flaB3, a putative fliD homologue was found, probably encoding the flagellar cap protein of Treponema maltophilum. Flagellin-gene-specific DNA probes hybridized to all 13 Treponema strains investigated, whereas a fliD-specific DNA probe only hybridized to Treponema maltophilum, other treponemal group IV isolates and Treponema brennaborense.

Taxonomy and virulence of oral spirochetes

All oral spirochetes are classified in the genus Treponema. This genus is in the family Spirochaetaceae as in Bergey's manual of systematic bacteriology. Other generic members of the family include Spirochaeta, Cristispira and Borrelia. This conventional classification is in accord with phylogenetic analysis of the spirochetes based on 16S rRNA cataloguing. The oral spirochetes fall naturally within the grouping of Treponema. Only four species of Treponema have been cultivated and maintained reliably: Treponema denticola, Treponema pectinovorum, Treponema socranskii and Treponema vincentii. These species have valid names according to the rules of nomenclature except for Treponema vincentii, which only has had effective publication. The virulence factors of the oral spirochetes updated in this mini-review have been discussed within the following broad confines: adherence, cytotoxic effects, iron sequestration and locomotion. T. denticola has been shown to attach to human gingival fibroblasts, basement membrane proteins, as well as other substrates by specific attachment mechanisms. The binding of the spirochete to human gingival fibroblasts resulted in cytotoxicity and cell death due to enzymes and other proteins. Binding of the spirochete to erythrocytes was accompanied by agglutination and lysis. Hemolysis releases hemin, which is sequestered by an outer membrane sheath receptor protein of the spirochete. The ability to locomote through viscous environments enables spirochetes to migrate within gingival crevicular fluid and to penetrate sulcular epithelial linings and gingival connective tissue. The virulence factors of the oral spirochetes proven in vitro underscore the important role they play in the periodontal disease process. This role has been evaluated in vivo by use of a murine model.

Insertional inactivation of Treponema denticola tap1 results in a nonmotile mutant with elongated flagellar hooks

The treponemal fla operon is comprised of numerous motility-related genes; however, the initial gene of this operon, tap1, has no known function. A recently developed system to generate specific mutants in Treponema denticola was utilized to determine if Tap1 was essential for motility. T. denticola tap1 and flanking DNA were identified, cloned, and sequenced, and a suicide plasmid that contained tap1 interrupted with an erythromycin resistance cassette (ermF and ermAM) was constructed. Because of potential polar effects from this cassette, a second plasmid that contained tap1 interrupted with a modified erythromycin resistance cassette that lacked the putative ermF transcription terminator was constructed. Electroporation-mediated allelic exchange incorporated the interrupted tap1 genes into the T. denticola chromosome, creating Tap1-deficient mutants. Reverse transcriptase PCR revealed that the erythromycin resistance cassette within tap1 did not terminate fla operon transcription in either mutant. Moreover, the phenotypes of the two mutants were indistinguishable. These mutants lacked motion in liquid culture, were unable to spread on agar plates, and lacked flagellar filaments as determined by electron microscopy. Immunoblots revealed a marked reduction in detectable FlaB flagellar filament protein compared to that of wild type; however, flaB RNA was easily detectable, and transcription levels did not appear to be altered. The basis for the lack of filament protein expression is unknown. Immunoblotting also showed that the flagellar hook protein (FlgE) was synthesized in the Tap1-deficient mutant; however, electron microscopy revealed that the mutant possessed unusual elongated hooks of variable lengths. We propose that treponemal Tap1 is analogous to FliK, which is involved in monitoring the flagellar hook length of Salmonella typhimurium.

Effect of temperature and viscosity on the motility of the spirochete Treponema denticola

Treponema denticola is an oral spirochete associated with periodontal diseases. Because bacterial motility is likely to be a potential virulence factor, we investigated the effect of viscosity and temperature on cell speed. In agreement with the work of others, translational motility was a function of the macroscopic viscosity of the medium. In addition, we found that although the speed of spirochetes was slow at 25 degrees C (4 microns s-1), it increased quite markedly at 35 degrees C (19 microns s-1). The results indicate that both viscosity and temperature are critical factors in T. denticola translational motility.

Characterization of flaA- and flaB- mutants of Serpulina hyodysenteriae: both flagellin subunits, FlaA and FlaB, are necessary for full motility and intestinal colonization

Motility of Serpulina hyodysenterlae is thought to play a pivotal role in the enteropathogenicity of this spirochete. To test this, a series of isogenic mutants containing specifically disrupted flagellar alleles (flaA1 and flaB1) were constructed and examined for virulence and ability to colonize the intestinal tract of mice. Mice challenged with the wild-type, parent strain showed a dose-related response to the challenge organism. In contrast, all flagellar mutant strains demonstrated aberrant motility in vitro and a significantly reduced ability to colonize and infect mice. To some extent, this degree of reduction in colonizing ability was dependent on the wild-type background strain used for mutant construction. A flaB1- strain generated from a 'laboratory isolate' was unable to colonize the mouse gut even at high challenge doses, although its parent was virulent for mice. However, when the same parent strain was 'animal-passed' prior to disruption of flaB1, the resulting flaB1- strain was able to transiently colonize the mouse gut and induce intestinal lesions. A comparison of a series of flagellar mutants constructed using the animal-passed parent strain further revealed that specific inactivation of flaB1 resulted in a more pronounced reduction in virulence and colonizing ability than that which occurred with two flaA1 mutants. Taken together, these data suggest that motility is an essential virulence factor of S. hyodysenteriae and that both sheath and core flagellin subunits, FlaA and FlaB, are necessary for full motility and intestinal colonization.

Genetic and transcriptional analysis of flgB flagellar operon constituents in the oral spirochete Treponema denticola and their heterologous expression in enteric bacteria

Oral spirochetes possess many potential virulence factors, including the capacity for tissue invasion and persistence despite a vigorous host immune response. In an attempt to identify treponemal immunoreactive components, sera derived from individuals with advanced periodontal disease were used as a reagent to isolate recombinant bacteriophage lambda clones expressing antigens of the oral spirochete Treponema denticola ATCC 35405. Nucleotide sequence analysis of a clone expressing three immunoreactive products has revealed seven T. denticola genes which appear to encode homologs of flagellar basal body constituents, FlgB, FlgC, FliE, and FliF, a flagellar switch component, FliG, and the putative flagellar export proteins, FliH and FliI, initially characterized in Salmonella typhimurium. Also identified was a gene resembling fliJ. Primer extension analysis identified a transcriptional start site 5' to the treponemal flgB gene. Appropriately spaced with respect to this start site was a sigma28 binding motif. The absence of additional identifiable sigma factor binding motifs within the treponemal sequence and the proximity of adjacent genes suggested operonic arrangement, and reverse transcriptase PCR provided evidence of cotranscription. Supporting the identification of these genes as flagellar components, heterologous expression in enteric bacteria of the putative switch basal body genes from T. denticola interfered with motility. Specifically, the presence of a plasmid expressing treponemal fliG reduced swarming motility in S. typhimurium, while in Escherichia coli, this plasmid conferred a nonmotile phenotype and a reduction in flagellar number. Thus, while spirochetal flagella are subject to unique synthetic and functional constraints, the organization of flagellar genes and the presence of sigma28-like elements are reminiscent of the flagellar systems of other bacteria, and there appears to be sufficient conservation of constituent proteins to allow interaction between T. denticola switch-basal body proteins and the flagellar machinery of gram-negative bacteria.

Relationship of Treponema denticola periplasmic flagella to irregular cell morphology

Treponema denticola is an anaerobic, motile, oral spirochete associated with periodontal disease. We found that the periplasmic flagella (PFs), which are located between the outer membrane sheath and cell cylinder, influence its morphology in a unique manner. In addition, the protein composition of the PFs was found to be quite complex and similar to those of other spirochetes. Dark-field microscopy revealed that most wild-type cells had an irregular twisted morphology, with both planar and helical regions, and a minority of cells had a regular right-handed helical shape. High-voltage electron microscopy indicated that the PFs, especially in those regions of the cell which were planar, wrapped around the cell body axis in a right-handed sense. In those regions of the cell which were helical or irregular, the PFs tended to lie along the cell axis. The PFs caused the cell to form the irregular shape, as two nonmotile, PF-deficient mutants (JR1 and HL51) were no longer irregular but were right-handed helices. JR1 was isolated as a spontaneously occurring nonmotile mutant, and HL51 was isolated as a site-directed mutant in the flagellar hook gene flgE. Consistent with these results is the finding that wild-type cells with their outer membrane sheath removed were also right-handed helices similar in shape to JR1 and HL51. Purified PFs were analyzed by two-dimensional gel electrophoresis, and several protein species were identified. Western blot analysis using antisera to Treponema pallidum PF proteins along with N-terminal amino acid sequence analysis indicated T. denticola PFs are composed of one class A sheath protein of 38 kDa (FlaA) and three class B proteins of 35 kDa (FlaB1 and FlaB2) and one of 34 kDa (FlaB3). The N-terminal amino acid sequences of the FlaA and FlaB proteins of T. denticola were most similar to those of T. pallidum and Treponema phagedenis. Because these proteins were present in markedly reduced amounts or were absent in HL51, PF synthesis is likely to be regulated in a hierarchy similar to that found for flagellar. synthesis in other bacteria.

Dual flaA1 flaB1 mutant of Serpulina hyodysenteriae expressing periplasmic flagella is severely attenuated in a murine model of swine dysentery

The motility imparted by the periplasmic flagella (PF) of Serpulina hyodysenteriae is thought to play a pivotal role in the enteropathogenicity of this spirochete. The complex PF are composed of multiple class A and class B polypeptides. Isogenic strains containing specifically disrupted flaAl or flaB1 alleles remain capable of expressing PF, although such mutants display aberrant motility in vitro. To further examine the role that these proteins play in the maintenance of periplasmic flagellar structural integrity, motility, and fitness for intestinal colonization, we constructed a novel strain of S. hyodysenteriae which is deficient in both FlaA1 and FlaB1. To facilitate construction of this strain, a chloramphenicol gene cassette, with general application as a selectable marker in prokaryotes, was developed. The cloned flaAl and flaB1 genes were disrupted by replacement of internal fragments with chloramphenicol and kanamycin gene cassettes, respectively. The inactivated flagellar genes were introduced into S. hyodysenteriae, and allelic exchange at the targeted chromosomal flaA1 and flaB1 loci was verified by PCR analysis. Immunoblots or cell lysates with antiserum raised against purified FlaA or FlaB confirmed the absence of the corresponding sheath and core proteins in this dual flagellar mutant. These mutations selectively abolished the expression of the targeted genes without affecting the synthesis of other immunologically related FlaB proteins. The resulting flaA1 flaB1 mutant exhibited altered motility in vitro. Surprisingly, it was capable of assembling periplasmic flagella that were morphologically normal as evidenced by electron microscopy. The virulence of this strain was assessed in a murine model of swine dysentery by determining the incidence of cecal lesions and the persistence of S. hyodysenteriae in the gut. Mice challenged with the wild-type strain or a passage control strain showed a dose-related response to the challenge organism. The dual flagellar mutant was severely attenuated in murine challenge experiments, suggesting that the FlaA1 and FlaB1 proteins are dispensable for flagellar assembly but critical for normal flagellar function and colonization of mucosal surfaces of the gastrointestinal tract. This strain represents the first spirochete engineered to contain specifically defined mutations in more than one genetic locus.

Evidence for two distinct locomotory phenotypes of Treponema denticola ATCC 35405

Using a two-layer system, a bottom layer containing treponema cells suspended in NOS (New Oral Spirochete)-Noble agar medium or NOS-Bacto agar medium and overlaid with cell-free NOS-agarose medium resulted in the spirochete cells migrating into the top layer. However, if the positions of the medium layers were reversed with the cells inoculated into the bottom layer containing NOS-agarose, there was no migration into the upper layer. This suggests migration of the spirochetes away from Bacto and Noble agars. Using a 3-layer system in which cells were inoculated into a middle layer consisting of NOS-agarose medium and sandwiched between cell-free NOS-agarose medium layers, cells remained within the middle layer. If the cells were inoculated into a middle layer consisting of NOS-Bacto agar medium while the upper and lower layers remained unchanged, cells migrated into both upper and lower layers. If cells that had migrated into the upper layer were transferred into a middle layer, they virtually all migrated into the upper layer repeatedly. Cells that had migrated into the lower layer and transferred to the middle layer migrated repeatedly into the lower layer. These results suggest the possible existence of two distinct locomotory phenotypes within this strain of treponeme.

Binding of host-associated treponeme proteins to collagens and laminin: a possible mechanism of spirochetal adherence to host tissues

The polypeptides of seven strains of human treponemes were investigated by immunoblot analysis for their binding to the human placental collagens and laminin. Of the treponemal polypeptides, eleven polypeptides, 45-kDa, 49-kDa, and 62-kDa polypeptides from T. pallidum ATCC 27087, a 48-kDa polypeptide from T. phagedenis biotype Reiter, 51-kDa and 53-kDa polypeptides from T. vincentii ATCC 35580, 30-kDa, 53-kDa and 63-kDa polypeptides from T. socranskii subsp. buccale ATCC 35534, a 52-kDa polypeptide from T. denticola ATCC 35405, and a 53-kDa polypeptide from T. denticola ATCC 33520 possessed an ability to bind to the laminin, type I, III, IV, or V collagen. An intermediate-sized human oral isolate strain G7201 did not possess any laminin- or collagen-binding polypeptides. Immunoelectron microscopy using intact treponemal cells with a single collagen-binding polypeptide and the corresponding antisera demonstrated that the 51-kDa and 53-kDa polypeptides from T. vincentii, the 53-kDa polypeptide from T. socranskii subsp. buccale ATCC 35534 and the 52-kDa polypeptide from T. denticola ATCC 35405, were outer envelope proteins.