Isolation of a major cell envelope protein from Fusobacterium nucleatum

The FomA porin from Fusobacterium nucleatum is a Toll-like receptor 2 agonist with immune adjuvant activity

Many bacterial components selectively activate immune and nonhematopoietic target cells via Toll-like receptor (TLR) signaling; modulation of such host responses defines the immune adjuvant properties of these bacterial products. For example, the outer membrane protein porins from Neisseria, Salmonella, and Shigella are known TLR2 agonists with established systemic and mucosal immune adjuvanticity. Early work indicated that the FomA porin from Fusobacterium nucleatum has immune adjuvant activity in mice. Using a purified recombinant FomA, we have verified its immune stimulatory properties and have defined a role for TLR2 signaling in its in vitro and in vivo activity. FomA induces interleukin 8 (IL-8) secretion and NF-κB-dependent luciferase activity in HEK cells expressing TLR2, IL-6 secretion, and cell surface upregulation of CD86 and major histocompatibility complex (MHC) II in primary B cells from wild-type mice, but it fails to activate cells from TLR2 knockout mice. Accordingly, the immune adjuvant activity of FomA is also TLR2 dependent. In a mouse model of immunization with ovalbumin (OVA), FomA induces enhanced production of OVA-specific IgM and IgG, including IgG1 and IgG2b antibodies, as well as enhanced secretion of IL-10 and IL-6, consistent with a Th2-type adjuvant effect. We also observe a moderate production of anti-FomA antibodies, suggesting that FomA is also immunogenic, a quality that is also TLR2 dependent. Therefore, modulation of host immune responses by FomA may be effective for targeting general host immunity not only to pathogens (as a novel TLR2 adjuvant) but also to F. nucleatum itself (as an antigen), expanding its use as a self-adjuvanted antigen in an immunization strategy against polymicrobial infections, including those by F. nucleatum.

Taxonomy, biology, and periodontal aspects of Fusobacterium nucleatum

The pathogenic potential of Fusobacterium nucleatum and its significance in the development of periodontal diseases, as well as in infections in other organs, have gained new interest for several reasons. First, this bacterium has the potential to be pathogenic because of its number and frequency in periodontal lesions, its production of tissue irritants, its synergism with other bacteria in mixed infections, and its ability to form aggregates with other suspected pathogens in periodontal disease and thus act as a bridge between early and late colonizers on the tooth surface. Second, of the microbial species that are statistically associated with periodontal disease, F. nucleatum is the most common in clinical infections of other body sites. Third, during the past few years, new techniques have made it possible to obtain more information about F. nucleatum on the genetic level, thereby also gaining better knowledge of the structure and functions of the outer membrane proteins (OMPs). OMPs are of great interest with respect to coaggregation, cell nutrition, and antibiotic susceptibility. This review covers what is known to date about F. nucleatum in general, such as taxonomy and biology, with special emphasis on its pathogenic potential. Its possible relationship to other periodontal bacteria in the development of periodontal diseases and the possible roles played by OMPs are considered.

Taxonomy, biology, and periodontal aspects of Fusobacterium nucleatum

The pathogenic potential of Fusobacterium nucleatum and its significance in the development of periodontal diseases, as well as in infections in other organs, have gained new interest for several reasons. First, this bacterium has the potential to be pathogenic because of its number and frequency in periodontal lesions, its production of tissue irritants, its synergism with other bacteria in mixed infections, and its ability to form aggregates with other suspected pathogens in periodontal disease and thus act as a bridge between early and late colonizers on the tooth surface. Second, of the microbial species that are statistically associated with periodontal disease, F. nucleatum is the most common in clinical infections of other body sites. Third, during the past few years, new techniques have made it possible to obtain more information about F. nucleatum on the genetic level, thereby also gaining better knowledge of the structure and functions of the outer membrane proteins (OMPs). OMPs are of great interest with respect to coaggregation, cell nutrition, and antibiotic susceptibility. This review covers what is known to date about F. nucleatum in general, such as taxonomy and biology, with special emphasis on its pathogenic potential. Its possible relationship to other periodontal bacteria in the development of periodontal diseases and the possible roles played by OMPs are considered.

Extraction, purification, and characterization of major outer membrane proteins from Wolinella recta ATCC 33238

The outer membrane of Wolinella recta ATCC 33238 was isolated by French pressure cell disruption and differential centrifugation. Outer membrane proteins (OMPs) were solubilized by Zwittergent 3.14 extraction and separated by DEAE-Sephacel ion-exchange chromatography. The major OMPs that were found in W. recta ATCC 33238 and in several other Wolinella spp. consisted of proteins with apparent molecular masses of 51, 45, and 43 kDa. These three conserved proteins were purified to essential homogeneity by one- and two-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and characterized chemically. Heating at between 75 and 100 degrees C revealed both the 43- and 51-kDa proteins to be heat modified from apparent molecular masses of 32 and 38 kDa, respectively. The 45-kDa protein was unmodified at all temperatures tested. Two-dimensional isoelectric focusing-SDS-PAGE revealed the 51-kDa protein to be composed of multiple pIs between a pH of 5.0 and greater than 8.0 while the 43- and 45-kDa proteins had a pI of approximately 6.0. N'-terminal amino acid sequence analysis of the first 30 to 40 amino acids and search of the Protein Identification Resource data base for similar proteins only revealed the 43-kDa protein to be similar to the P.69 OMP of Bordetella pertussis; however, the homology was weak (33%). Amino acid analysis revealed the 43-kDa protein to be noncharged and the 45- and 51-kDa proteins to be hydrophilic, containing between 38 to 42% polar residues but no cysteine. This study reports the purification and partial characterization of three conserved proteins in W. recta ATCC 33238.

Factors in virulence expression and their role in periodontal disease pathogenesis

The classic progression of the development of periodontitis with its associated formation of an inflammatory lesion is characterized by a highly reproducible microbiological progression of a Gram-positive microbiota to a highly pathogenic Gram-negative one. While this Gram-negative microbiota is estimated to consist of at least 300 different microbial species, it appears to consist of a very limited number of microbial species that are involved in the destruction of periodontal diseases. Among these "putative periodontopathic species" are members of the genera Porphyromonas, Bacteroides, Fusobacterium, Wolinella, Actinobacillus, Capnocytophaga, and Eikenella. While members of the genera Actinomyces and Streptococcus may not be directly involved in the microbial progression, these species do appear to be essential to the construction of the network of microbial species that comprise both the subgingival plaque matrix. The temporal fluctuation (emergence/disappearance) of members of this microbiota from the developing lesion appears to depend upon the physical interaction of the periodontal pocket inhabitants, as well as the utilization of the metabolic end-products of the respective species intimately involved in the disease progression. A concerted action of the end-products of prokaryotic metabolism and the destruction of host tissues through the action of a large number of excreted proteolytic enzymes from several of these periodontopathogens contribute directly to the periodontal disease process.(ABSTRACT TRUNCATED AT 250 WORDS)

Growth conditions and outer membrane proteins of Fusobacterium nucleatum

Fusobacterium nucleatum strains ATCC 10953, ATCC 25586, F1 F3, F6, and Fev1 were grown in different media. The influence of growth conditions on the outer membrane proteins (OMPs) was analyzed by sodium dodecyl sulfate--polyacrylamide gel electrophoresis (SDS-PAGE). There were no apparent differences in the outer membrane protein profiles when cells in the same phase of growth in various rich media were compared. Differences, however, were observed between early logarithmic phase and stationary phase cells. Thus several proteins were only synthesized during late logarithmic and stationary phase. Synthesis of some of these proteins, in particular a 65K and a 14K protein, seemed to depend on the presence of peptides in the medium. In a complete medium, these proteins were synthesized after depletion of some amino acids, and peptides were then utilized.

Outer membrane proteins as major antigens of Fusobacterium nucleatum

The immunochemical reactions of rabbit polyclonal antibodies directed to different preparations of Fusobacterium nucleatum i.e, whole cells, peptidoglycan associated proteins, a peptidoglycan-protein complex and a purified 40 kiloDalton (kDa) protein, were investigated on outer membrane preparations of Fusobacterium species and a restricted number of Leptotrichia buccalis after their separation on sodium dodecyl sulphate polyacrylamide gels and electrotransfer to nitrocellulose. All F. nucleatum strains had identical reaction patterns with the immune sera tested. Surface exposed parts of a restricted number of proteins with apparent molecular weights at 70 kDa (a doublet band), 60 kDa, 55 kDa and 40 kDa seemed to be major immunogens. Antigenic related proteins either of identical or slightly deviating electrophoretic mobilities to the 40-kDa protein were observed with the other members of Bacteroidaceae tested. The characteristic 70-kDa protein doublet seemed to be restricted to F. nucleatum although single protein bands of near identical molecular weights belonging to the other species tested also reacted. The data also indicate that the 60-kDa and 55-kDa polypeptides might be present in other species of Fusobacterium.

Coaggregation of Fusobacterium nucleatum, Selenomonas flueggei, Selenomonas infelix, Selenomonas noxia, and Selenomonas sputigena with strains from 11 genera of oral bacteria

Twenty-eight strains of Fusobacterium nucleatum and 41 Selenomonas strains, including S. sputigena (24 strains), S. flueggei (10 strains), S. infelix (5 strains), and S. noxia (2 strains), were tested for their ability to coaggregate with each other and with 49 other strains of oral bacteria representing Actinobacillus, Actinomyces, Bacteroides, Capnocytophaga, Gemella, Peptostreptococcus, Porphyromonas, Propionibacterium, Rothia, Streptococcus, and Veillonella species. Selenomonads coaggregated with fusobacteria and with Actinomyces naeslundii PK984 but not with any of the other bacteria, including other selenomonads. In contrast, fusobacteria coaggregated with members of all genera, although not with all strains of each species tested. Each fusobacterium strain appeared to have its own set of partners and coaggregation properties, unlike their partners, whose coaggregation properties in earlier surveys delineated distinct coaggregation groups. Coaggregations of fusobacteria with the 63 gram-negative strains were usually inhibited by EDTA, whereas those with the 27 gram-positive strains were usually not inhibited. Likewise, lactose-inhibitable coaggregations were common among some strains of fusobacteria and some strains from each of the genera containing gram-negative partners but were rarely observed with gram-positive partners. Heating the fusobacteria at 85 degrees C for 30 min completely prevented coaggregation with most partners, suggesting the involvement of a protein on the fusobacteria. Heat treatment of many of the gram-negative partners not only enhanced their coaggregation with the fusobacteria but also changed lactose-sensitive coaggregations to lactose-insensitive coaggregations. Although fusobacteria coaggregated with a broader variety of oral partner strains than any other group of oral bacteria tested to date, each fusobacterium exhibited coaggregation with only a certain set of partner strains, and none of the fusobacteria adhered to other strains of fusobacteria, indicating that recognition of partner cell surfaces is selective. The strains of F. nucleatum are heterogeneous and cannot be clustered into distinct coaggregation groups. Collectively, these results indicate that coaggregation between fusobacteria and many gram-negative partners is significantly different from their coaggregation with gram-positive partners. The contrasting variety of partners for fusobacteria and selenomonads supports the concept of coaggregation partner specificity that has been observed with every genus of oral bacteria so far examined.

Isolation of a corncob (coaggregation) receptor polypeptide from Fusobacterium nucleatum

Corncobs, which are distinct morphological units formed by the ordered coaggregation of a filamentous microorganism and streptococci, can be made in vitro by using oral strains of Fusobacterium nucleatum and Streptococcus sanguis. Previous studies have shown that strains of F. nucleatum contain one of at least two different types of corncob receptor. The objective of this study was to isolate the receptor from F. nucleatum ATCC 10953 as the first step in the elucidation of the molecular basis of corncob formation. The cell envelope fraction from this bacterium was treated with trypsin, delipidated with chloroform-methanol, and subjected to ion-exchange chromatography. A single polypeptide (apparent Mr, 39,500), which was eluted from the column with 0.5 M sodium chloride and extracted with dodecyltrimethylammonium bromide to remove contaminating lipopolysaccharide, inhibited corncob formation between strain ATCC 10953 and S. sanguis CC5A. Similarly derived cell fractions from either F. nucleatum FDC 364 or Fusobacterium necrophorum failed to effect coaggregation in the inhibition assay. Amino acid analysis of the polypeptide showed a moderately hydrophobic character (polarity index, 41) and 11% basic residues. Antiserum made against the purified polypeptide agglutinated F. nucleatum ATCC 10953, neutralized the ability of this bacterium to form corncobs, and agglutinated whole cells of S. sanguis CC5A that were precoated with the receptor polypeptide. The identification and isolation of this receptor should greatly enhance our ability to define some of the complex intergeneric coaggregation mechanisms that are thought to occur in the human oral cavity.

Utilization of amino acids and peptides by Fusobacterium nucleatum

Fusobacterium nucleatum strains ATCC 10953, Fevl, F1, F3, and F6 utilized amino acids, in particular glutamate, histidine, and aspartate were common to all strains. Strain differences were observed in the utilization of threonine, serine, lysine, tyrosine, and methionine, and only strain ATCC 10953 utilized all these amino acids. The glutamate and histidine pools were in all cases fully depleted before the other amino acids were attacked and at the same time all strains except 10953 started to utilize peptides at a noticeable rate. For strain Fevl, glutamyl- and aspartyl-containing peptides seemed to be of considerable nutritional importance, and this strain did not grow on a medium based on amino acids alone. On the other hand, strain 10953 did not utilize any peptides to a noticeable extent, and it could grow on an amino acid based medium.

Immunobiological activities of a porin fraction isolated from Fusobacterium nucleatum ATCC 10953

From Fusobacterium nucleatum ATCC 10953 cell envelope fraction whose inner membranes had been removed by treatment with sodium N-lauroyl sarcosinate, an outer membrane protein (37,000 Mr in a native state) was prepared by extraction with lithium dodecyl sulfate. The protein thus obtained showed distinct porin activity, namely, the ability to form hydrophilic diffusion pores by incorporation into the artificial liposome membrane. The porin fraction exhibited strong immunobiological activities in the in vitro assays: B-cell mitogenicity and polyclonal B-cell activation on murine splenocytes, stimulatory effects on guinea pig peritoneal macrophages, and enhancement of the migration of human blood monocytes. The porin fraction also exhibited immunoadjuvant activity to increase the antibody production against sheep erythrocytes in the spleen of mice that were immunized by sheep erythrocytes with porin. Although chemical analyses revealed that the test porin fraction contained a considerable amount of lipopolysaccharide (LPS) (around 12% of the fraction), the studies with LPS-nonresponding C3H/HeJ mice and on the inhibitory effects of polymyxin B strongly suggest that most of the above bioactivities are due to porin protein itself, not to coexistent LPS in the porin fraction.

Partial characterization of a peptidoglycan-protein complex from Fusobacterium nucleatum Fev1

A protein in the cell wall of Fusobacterium nucleatum Fev1 remained associated with the peptidoglycan during extraction with various detergents and organic solvents. On digestion of this peptidoglycan-protein complex (PPC) with murein hydrolases, sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) showed polypeptide bands with apparent molecular weights (MWs) in the range of 3000 to 40,000. After reaction with maleic anhydride the electrophoretic mobilities of these polypeptide bands increased to those of MWs 3000 to 12,000. The PPC protein showed a limited susceptibility toward trypsin, giving polypeptides that migrated in SDS-PAGE as a diffuse band with MW in the range of 3000 to 6000. The amino acid composition of all polypeptide bands eluted from SDS-PAGE was very similar, whichever enzyme was used for the solubilization of the PPC, and was nearly identical to that found for the protein moiety of the PPC. On the basis of a MW of 3000 for a protein unit, about one molecule of protein was found per five peptidoglycan subunits. Lanthionine was not found associated with released polypeptide, and muramic acid and glucosamine were either absent or present in amounts less than one molecule per protein unit. The PPC was immunogenic in rabbits, and purified anti-PPC IgG reacted with murein hydrolase-released protein separated on SDS-PAGE but preferentially with bands of MWs greater than 18,000.