Cloning of Bacteroides gingivalis surface antigens involved in adherence

Hydrogen Sulfide, Oxidative Stress and Periodontal Diseases: A Concise Review

In the past years, biomedical research has recognized hydrogen sulfide (H₂S) not only as an environmental pollutant but also, along with nitric oxide and carbon monoxide, as an important biological gastransmitter with paramount roles in health and disease. Current research focuses on several aspects of H₂S biology such as the biochemical pathways that generate the compound and its functions in human pathology or drug synthesis that block or stimulate its biosynthesis. The present work addresses the knowledge we have to date on H₂S production and its biological roles in the general human environment with a special focus on the oral cavity and its involvement in the initiation and development of periodontal diseases.

Bacteria-derived hydrogen sulfide promotes IL-8 production from epithelial cells

Hydrogen sulfide (H(2)S), a volatile sulfur compound, is implicated as a cause of inflammation, especially when it is produced by bacteria colonizing gastrointestinal organs. However, it is unclear if H(2)S produced by periodontal pathogens affects the inflammatory responses mediated by oral/gingival epithelial cells. Therefore, the aims of this study were (1) to compare the in vitro production of H(2)S among 14 strains of oral bacteria and (2) to evaluate the effects of H(2)S on inflammatory response induced in host oral/gingival epithelial cells. Porphyromonas gingivalis (Pg) produced the most H(2)S in culture, which, in turn, resulted in the promotion of proinflammatory cytokine IL-8 from both gingival and oral epithelial cells. The up-regulation of IL-8 expression was reproduced by the exogenously applied H(2)S. Furthermore, the mutant strains of Pg that do not produce major soluble virulent factors, i.e. gingipains, still showed the production of H(2)S, as well as the promotion of epithelial IL-8 production, which was abrogated by H(2)S scavenging reagents. These results demonstrated that Pg produces a concentration of H(2)S capable of up-regulating IL-8 expression induced in gingival and oral epithelial cells, revealing a possible mechanism that may promote the inflammation in periodontal disease.

Role of a Tannerella forsythia exopolysaccharide synthesis operon in biofilm development

Tannerella forsythia is a Gram-negative oral anaerobe implicated in the development of periodontitis, a chronic inflammatory disease induced by bacterial infections which leads to tooth loss if untreated. Since biofilms formed by periodontal bacteria are considered important in disease progression and pose difficulties in treatment, we sought to investigate the underlying mechanisms of T. forsythia biofilm formation. This was carried out by screening random insertion mutants of T. forsythia for alterations in biofilm development. This approach lead to the identification of an operon involved in exopolysaccharide (EPS) synthesis. An isogenic mutant of one of the genes, wecC, contained within the operon was constructed. The isogenic wecC mutant showed increased ability to form biofilms as compared to the parent strain. The wecC mutant also formed aggregated microcolonies and showed increased cell-surface associated hydrophobicity as compared to the parent strain. Moreover, biochemical characterization of the wecC mutant indicated that glycosylation of surface glycoproteins was reduced. Therefore, our results suggest that the wecC operon is associated with glycosylation of surface-glycoprotein expression and likely plays an inhibitory role in T. forsythia biofilm formation.

Fimbriae of Porphyromonas gingivalis induce opsonic antibodies that significantly enhance phagocytosis and killing by human polymorphonuclear leukocytes

Porphyromonas gingivalis has been strongly implicated in the pathogenesis of human periodontitis. Fimbriae mediate adherence and colonization of the oral cavity by this organism and may, therefore, have potential for use as antigen in an anti-P. gingivalis vaccine. The purpose of our study was to determine whether P. gingivalis fimbriae have opsonic target sites and whether they are accessible on the cell surfaces and cross-reactive among P. gingivalis fimbrial types and serotypes. Rabbits were immunized with a vaccine. The antiserum reacted with a 43-kDa fimbrillin monomer and a 43-kDa component in whole-cell sonicates of P. gingivalis 33277, but it showed only very weak reactivity in the 43-kDa region of Western blots of a whole-cell sonicate of strain DPG3, a mutant that does not express functional fimbriae. The antibody enhanced chemiluminescence approximately six-fold relative to preimmune serum values and significantly enhanced phagocytosis and killing of P. gingivalis 33277 by human polymorphonuclear leukocytes. Peak opsonic activity was observed at week 6 followed by a plateau that remained until week 16. The fimbria-deficient mutant DPG3 did not bind antifimbrial antibody and was not opsonized, whereas strain 381, the parent of the mutant, was opsonized. The specific antibody bound to and opsonized P. gingivalis strains 33277 and 381 (fimbria type I) but not W50, A7A-1-28, 9-14K-1 or FAY-19M-1 (fimbrial types II-V). Specific antibody bound to strain 2561 (fimbrial type I) but, as assessed by chemiluminescence, did not opsonize it. While fimbriae have opsonic target sites that are accessible on P. gingivalis cell surfaces, the relevant opsonic target sites do not appear to be shared across serotypes or fimbrial types. Thus, a vaccine containing, as antigen, fimbrial protein from a single P. gingivalis strain would likely be ineffective against infections by P. gingivalis strains expressing other fimbrial types.

Functional characteristics of antibodies induced by Arg-gingipain (HRgpA) and Lys-gingipain (Kgp) from Porphyromonas gingivalis

Arginine-specific gingipain (HRgpA) and lysine-specific gingipain (Kgp), enzymes produced by Porphyromonas gingivalis, may be candidates for an anti-P. gingivalis vaccine. The purpose of our study was to determine whether HRgpA and Kgp have opsonic target sites and whether these sites are available and accessible on intact P. gingivalis cells. Rabbits were used to generate polyclonal antibodies to both proteins. Animals were immunized and immunoglobulin G (IgG) fractions were isolated from preimmune and immune sera. Functional characteristics of the antibodies were assessed by determining antibody titers by enzyme-linked immunosorbent assay (ELISA), generating Western immunoblots, and measuring antibody enhancement of P. gingivalis opsonization, phagocytosis and killing by polymorphonuclear leukocytes (PMN) of intact cells of strains of P. gingivalis representative of the four serotypes. Strains studied included 33277 (serotype A), A7A1-28 (serotype B), W50 (serotype C) and 381 (serotype D). Both HRgpA and Kgp induced high titers of IgG antibody. Anti-HRgpA and anti-Kgp bound to both HRgpA and Kgp demonstrating a large proportion of shared antigenic epitopes. The two antibodies bound equally well to all four P. gingivalis serotypes with titers ranging from 77 to 205 ELISA units when compared to preimmune IgG set at 1 ELISA unit. The immunoblot patterns of binding of the two antibodies to HRgpA and Kgp and to sonicates of the four P. gingivalis serotypes were virtually identical. Both antibodies detected components in HRgpA at 27, 35 and 45 kDa and in Kgp at 27, 32, 35, 40 and 55 kDa. The antibodies also detected components at or near these same positions in addition to multiple high molecular mass components in the cell sonicates of P. gingivalis. Both proteins induced antibodies that significantly enhanced opsonization as assessed by chemiluminescence, with values ranging from 130 mV to 375 mV for anti-HRgpA IgG and from 240 mV to 475 mV for anti-Kgp IgG. Both antibodies significantly enhanced PMN-mediated bacterial killing of the four P. gingivalis serotypes, although the percentage of killing varied among the serotypes (24-81% for anti-HRgpA and 37-89% for anti-Kgp). Thus, both HRgpA and Kgp express opsonic target sites and induce high titers of antibodies that opsonize and enhance killing of all four serotypes of P. gingivalis. These two proteins appear to be potential candidate antigens for an anti-P. gingivalis vaccine.

The molecular cloning, nucleotide sequence and expression of an antigenic determinant from Porphyromonas gingivalis

A genomic library generated in Escherichia coli was probed with a monoclonal antibody (mAb) LDS28, which reacts with a species-specific cell-surface antigen of Porphyromonas gingivalis. A clone designated pGPR2.1 was shown to express a 46-kDa protein reactive with mAb LDS28, which maps to a 1.7-kb HincII fragment. DNA sequence analysis revealed pGPR2.1 contains a 5653-bp insert with six open reading frames, one of which shows significant DNA homology with the rnhB gene of E. coli. Several subclones of pGPR2.1 were randomly generated in plasmid vector pTTQ18* using restriction enzyme Sau3a. Immunoblotting of subclones demonstrated that the LDS28-reactive antigen was coded for by an open reading frame predicted to specify a protein of 455 amino acids (50 kDa). This open reading frame was designated pgaA (Porphyromonas gingivalis antigen). The predicted amino acid sequence of PgaA contains a putative ABC signature for binding NTPs as well as a predicted transmembrane domain. Minicell labelling of pGPR2.1-encoded proteins and subclone derivatives revealed that pgaA directs expression of protein of multiple molecular weights (31-46 kDa) from its own promoter in E. coli, and that some of these forms may be caused by proteolysis of a 50-kDa precursor which itself shows a reduced apparent molecular weight (46 kDa) on sodium dodecyl sulphate-polyacrylamide gel electrophoresis.

Oral immunization with recombinant Salmonella typhimurium expressing a cloned Porphyromonas gingivalis hemagglutinin: effect of boosting on mucosal, systemic and immunoglobulin G subclass response

Live avirulent Salmonella typhimurium are convenient vaccine vectors for the delivery of recombinant antigens for the induction of mucosal and systemic immunity. The hagB gene encodes a hemagglutinin of Porphyromonas gingivalis, a suspected causal agent in human adult periodontal disease. In previous studies, we have shown that hagB can be expressed in avirulent S. typhimurium and is immunogenic when given orally to mice. In this study, we evaluated recall responses in both serum and mucosal secretions after boosting. In addition, we have examined the immunoglobulin G (IgG) subclass response in serum to both HagB and the Salmonella carrier. Mice were orally immunized with S. typhimurium expressing the hagB gene and then boosted 14 weeks later. Responses were measured through 27 weeks. Both primary and recall IgG and IgA responses were seen in serum to the purified HagB as well as to the Salmonella carrier. Likewise, mucosal primary and recall responses were seen in saliva, fecal extracts and vaginal washes although the kinetics of the responses differed. The anti-HagB response in serum was dominated by IgG2a during the peak of primary response, prior to boosting and during the peak of the recall response. The anti-S. typhimurium response shifted from predominantly IgG3 following primary immunization to IgG2a after boosting. The IgG1 response was minimal against each antigen. This pattern of IgG subclass distribution is consistent with a Th1-type response. These data indicate that avirulent S. typhimurium is capable of delivering a putative virulence factor from P. gingivalis and inducing a primary and recall response in both serum and secretions and provides a means of studying P. gingivalis virulence factors and for the development of a potential vaccine.

The NAD(P)H-utilizing glutamate dehydrogenase of Bacteroides thetaiotaomicron belongs to enzyme family I, and its activity is affected by trans-acting gene(s) positioned downstream of gdhA

Previous studies have suggested that regulation of the enzymes of ammonia assimilation in human colonic Bacteroides species is coordinated differently than in other eubacteria. The gene encoding an NAD(P)H-dependent glutamate dehydrogenase (gdhA) in Bacteroides thetaiotaomicron was cloned and expressed in Escherichia coli by mutant complementation from the recombinant plasmid pANS100. Examination of the predicted GdhA amino acid sequence revealed that this enzyme possesses motifs typical of the family I-type hexameric GDH proteins. Northern blot analysis with a gdhA-specific probe indicated that a single transcript with an electrophoretic mobility of approximately 1.6 kb was produced in both B. thetaiotaomicron and E. coli gdhA+ transformants. Although gdhA transcription was unaffected, no GdhA enzyme activity could be detected in E. coli transformants when smaller DNA fragments from pANS100, which contained the entire gdhA gene, were analyzed. Enzyme activity was restored if these E. coli strains were cotransformed with a second plasmid, which contained a 3-kb segment of DNA located downstream of the gdhA coding region. Frameshift mutagenesis within the DNA downstream of gdhA in pANS100 also resulted in the loss of GdhA enzyme activity. Collectively, these results are interpreted as evidence for the role of an additional gene product(s) in modulating the activity of GDH enzyme activity. Insertional mutagenesis experiments which led to disruption of the gdhA gene on the B. thetaiotaomicron chromosome indicated that gdhA mutants were not glutamate auxotrophs, but attempts to isolate similar mutants with insertion mutations in the region downstream of the gdhA gene were unsuccessful.

Duplication and differential expression of hemagglutinin genes in Porphyromonas gingivalis

A third hemagglutinin gene, defined as hagC, was cloned from Porphyromonas gingivalis 381 and sequenced. This gene was found to encode a protein highly homologous (98.6%) to the previously reported HagB hemagglutinin protein. The upstream and downstream regions of hagB and hagC were found to share less than 40% homology compared with 99% for their open reading frames. The antigenic relationship between the two hemagglutinins was demonstrated by Western blot analysis. When expressed in an in vitro transcription-translation system, both genes encoded a protein with a molecular mass of 49 kDa. As determined by reverse transcription polymerase chain reaction, the steady-state levels of hagB and hagC mRNAs were found to vary according to the growth phase and hemin concentration. The amount of transcripts decreased in hemin-limited conditions or in the absence of hemin. Furthermore, hagB mRNAs were detected in the early logarithmic growth phase compared with the hagC transcripts, which were detected only in the mid-exponential phase of growth.

Restriction fragment length polymorphism analysis of two hemagglutinin loci, serotyping and agglutinating activity of Porphyromonas gingivalis isolates

Restriction fragment length polymorphisms (RFLPs) of two hemagglutinin loci were analyzed in 36 Porphyromonas gingivalis isolates from human and monkey origins using portions of hagA and hagB as probes. The P. gingivalis strains were differentiated into 9 RFLP groups based on the heterogeneity of the hagA locus and 10 different groups based on hybridization with hagB. Homology to hagA was detected in all human derived and all but three monkey derived strains. All P. gingivalis isolates exhibited DNA homologous to hagB. Multiple alleles of the hemagglutinin genes were detected for most P. gingivalis strains. No DNA homologous to either hemagglutinin gene could be detected in 6 other bacterial species tested. Serotyping and hemagglutination titers of each P. gingivalis isolate were obtained in an attempt to establish a correlation between these pheno-typic parameters and RFLP group. Although no correlations were found with these parameters, a correlation between RFLP group and invasiveness in the mouse abscess model was noted.

Characterization of recombinant and native forms of a cell surface antigen of Porphyromonas (Bacteroides) gingivalis

The cloning of genes encoding putative cell surface antigens of Porphyromonas gingivalis ATCC 33277 has been reported previously (B. C. McBride, A. Joe, and U. Singh, Arch. Oral Biol. 55:59S-68S, 1990). This study characterizes the recombinant protein rPgAg1, which is highly expressed in clone BA3, and the corresponding 51-kDa native antigen PgAg1. Cellular localization studies with monospecific antibodies to rPgAg1 in a Western immunoblot assay of a P. gingivalis membrane fraction and immunogold labeling of intact P. gingivalis cells confirmed the cell surface location of the native PgAg1 molecule. The pgag1 gene was found to be present in all four strains of P. gingivalis examined, and the gene product was expressed. Highly homologous DNA sequences and immunologically related proteins, however, were not detected in related species in the group formerly known as black-pigmented Bacteroides. This suggests that PgAg1 is specific to P. gingivalis and is highly conserved within this species. A protein data base search with the NH2-terminal amino acid sequence of rPgAg1 did not identify any significantly similar protein sequences. The high level of expression of rPgAg1 was not dependent on the insertional orientation of the cloned fragment. It therefore appears that a P. gingivalis promoter is present which is well recognized by the transcriptional apparatus of the Escherichia coli cloning host. The promoter element and structural gene for a specific cell surface antigen of P. gingivalis have been cloned.

Isolation and characterization of a cloned Porphyromonas gingivalis hemagglutinin from an avirulent strain of Salmonella typhimurium

Identification of surface macromolecules of Porphyromonas gingivalis that act as virulence factors in periodontal disease has important implications for studying host-parasite interactions as well as for potential vaccine development. The objective of this study was to determine whether a cloned, P. gingivalis hemagglutinin gene could be expressed in an intact form in an avirulent Salmonella typhimurium vaccine construct and to characterize the recombinant protein. The recombinant protein was purified from the vaccine strain, characterized, and tested for biological activity as a competitive inhibitor of hemagglutination. Cells of S. typhimurium SL3261/pST7 grown in Luria broth were broken by sonic disruption and fractionated. The purified recombinant protein was found to inhibit hemagglutination of erythrocytes by whole P. gingivalis cells. The same purified protein was analyzed for its N-terminal amino acid sequence and amino acid composition and found to match that predicted from the nucleotide sequence of the cloned gene. These results indicate that a surface macromolecule of P. gingivalis can be expressed in an intact and biologically active form in a Salmonella carrier strain.

Expression of Porphyromonas gingivalis proteolytic activity in Escherichia coli

Porphyromonas gingivalis (formerly Bacteroides gingivalis) degrades numerous protein substrates including collagen, fibrinogen, fibronectin, gelatin, casein, immunoglobulins and complement components. In order to clone one or more of these protease genes, a genomic library was constructed with Sau3A1 restriction fragments of chromosomal DNA from P. gingivalis ATCC 33277 ligated into the temperature-regulated vector pCQV2, and expressed in Escherichia coli DH5 alpha mcr. The electro-transformants (3 x 10(4)) were screened for general protease activity on Luria broth agar containing ampicillin (50 mg/l) and sodium caseinate (2%). One casein-hydrolyzing clone was detected and subcultured, and the activity of the cell extracts was characterized. We were able to show that the protease-positive clone, (pTEM1), had broad substrate specificity. Colorimetric assays indicated the hydrolysis of azocoll, azocasein, collagen, elastin-congo red and artificial substrates. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis was used to confirm that collagen, casein, fibrinogen and fibronectin were degraded by the clone.