Cloning and expression in Escherichia coli of the gene encoding the structural subunit of Bacteroides nodosus fimbriae

Characterization of two putative Dichelobacter nodosus footrot vaccine antigens identifies the first lysozyme inhibitor in the genus

The Gram-negative anaerobic bacterium Dichelobacter nodosus (Dn) causes footrot in ruminants, a debilitating and highly contagious disease that results in necrotic hooves and significant economic losses in agriculture. Vaccination with crude whole-cell vaccine mixed with multiple recombinant fimbrial proteins can provide protection during species-specific outbreaks, but subunit vaccines containing broadly cross-protective antigens are desirable. We have investigated two D. nodosus candidate vaccine antigens. Macrophage Infectivity Potentiator Dn-MIP (DNO_0012, DNO_RS00050) and Adhesin Complex Protein Dn-ACP (DNO_0725, DNO_RS06795) are highly conserved amongst ~170 D. nodosus isolates in the https://pubmlst.org/dnodosus/ database. We describe the presence of two homologous ACP domains in Dn-ACP with potent C-type lysozyme inhibitor function, and homology of Dn-MIP to other putative cell-surface and membrane-anchored MIP virulence factors. Immunization of mice with recombinant proteins with a variety of adjuvants induced antibodies that recognised both proteins in D. nodosus. Notably, immunization with fimbrial-whole-cell Footvax vaccine induced anti-Dn-ACP and anti-Dn-MIP antibodies. Although all adjuvants induced high titre antibody responses, only antisera to rDn-ACP-QuilA and rDn-ACP-Al(OH)₃ significantly prevented rDn-ACP protein from inhibiting lysozyme activity in vitro. Therefore, a vaccine incorporating rDn-ACP in particular could contribute to protection by enabling normal innate immune lysozyme function to aid bacterial clearance.

Cloning of a Lysobacter enzymogenes gene that encodes an arginyl endopeptidase (endoproteinase Arg-C)

Screening an expression library of Lysobacter enzymogenes DNA allowed us to clone a gene encoding a serine protease that cleaves synthetic substrates C-terminal to Arg and, to a lesser extent, Lys residues. The gene product, which shares sequence homology with the lysyl endopeptidases from L. enzymogenes and Achromobacter lyticus, consists of a signal sequence (24 residues), pro-region ( approximately 195 residues), and catalytic domain ( approximately 244 residues). Downstream of this gene is an open reading frame that lacks a promoter and appears to encode an inactive type I subtilase.

Electroporation-mediated transformation of the ovine footrot pathogen Dichelobacter nodosus

Studies on the potential virulence genes of the ovine footrot pathogen Dichelobacter nodosus have been hindered by the lack of a genetic system for this organism. In an attempt to accomplish the transformation of D. nodosus cells, we constructed a plasmid that contained part of a native D. nodosus plasmid and carried a tetracycline resistance gene that was located between the D. nodosus rrnA promoter and terminator. This plasmid was used to transform several D. nodosus strains to tetracycline resistance. Analysis of two independent transformants from each parental strain showed that in nearly all of these derivatives, the plasmid was not replicating independently, but that the tetracycline resistance gene had inserted by homologous recombination into one of the three rrn operons located on the chromosome. In most of the transformants, double reciprocal crossover events had occurred. These results are highly significant for genetic studies in D. nodosus and for footrot pathogenesis studies, since by using reverse genetics it will now be possible to examine the role of putative D. nodosus-encoded virulence genes in the disease process.

Identification and sequencing of the groE operon and flanking genes of Lawsonia intracellularis: use in phylogeny

Proliferative enteropathy (PE) is a complex of diseases of commercial importance to the pig industry. The obligate intracellular bacterium Lawsonia intracellularis is consistently associated with PE and pure cultures of this bacterium have been used to reproduce PE in pigs. In this study L. intracellularis bacteria were purified directly from PE-affected tissue. DNA extracted from purified bacteria was used to construct a partial genomic library which was screened using sera from L. intracellularis-immunized rabbits. Two seroreactive recombinant clones were identified, one of which expressed proteins of 10 and 60 kDa. The sequence of the insert from this clone, pISI-2, revealed ORFs with sequence similarity to the groES/EL operon of Escherichia coli, the 505 ribosomal proteins L21 and L27 of E. coli, a GTP-binding protein of Bacillus subtilis and a possible protoporphyrinogen oxidase, HemK, of E. coli. Primers designed from unique sequences from the pISI-2 insert amplified DNA from infected, but not non-infected, porcine ilea; the amplicon sequence obtained from tissue-cultured L. intracellularis was identical to the corresponding sequence in pISI-2, confirming the origin of the clone. The sequence of L. intracellularis GroEL and other GroEL sequences in the databases were used to construct a partial phylogenetic tree. Analysis of the GroEL sequence relationship suggested that L. intracellularis is not significantly related to other organisms whose GroEL sequences are held in the databases and supports previous data from 16S sequence analyses suggesting that L. intracellularis is a member of a novel group of enteric pathogens.

Molecular analysis of Dichelobacter nodosus isolated from footrot in sheep in Malaysia

Pulsed field gel electrophoresis analysis of genomic DNA was used to investigate genetic diversity among Dichelobacter nodosus from footrot in sheep in Malaysia. Twelve Dichelobacter nodosus strains isolated from lesion materials from infected sheep were confirmed as Dichelobacter nodosus by polymerase chain reaction technique using the species-specific Dichelobacter nodosus 16S RNA sequence Ac and C as primers. Pulsed field gel electrophoresis banding profiles using restriction enzymes ApaI (5'GGGCCC3'), SfiI (5'GGCCNNNNNGGCC3') and SmaI ('5CCCGGG3') enabled the 12 Dichelobacter nodosus strains to be differentiated into eight different PFGE patterns and thus genome-types, with F (coefficient of similarity) values ranging from 0.17 to 1.0 (ApaI), 0.14 to 1.0 (SfiI) and 0.22 to 1.0 (SmaI). Strains with origin in different farms were shown to have different PFGE patterns (two strains, M7 and M8 were the only exception). On the basis of their PFGE, all field strains used in the study differed from the reference strains. Our data revealed that there are several clonal types of Dichelobacter nodosus isolates and indicated that there is probably more than one source of this pathogen on the farms studied. The study showed that strains of D. nodosus exhibited considerable genetic diversity using this method and that genomic analysis by pulsed field gel electrophoresis was useful in discriminating the D. nodosus strains.

Physical and genetic map of the chromosome of Dichelobacter nodosus strain A198

A physical map of the chromosome of Dichelobacter nodosus strain A198 was constructed using the restriction endonucleases EagI and StuI. Mapping data indicated the presence of a single, circular chromosome of 1.54 Mb. The three rRNA operons and the virulence related locus (vrl) were precisely positioned at the junctions of EagI and StuI fragments, and their transcriptional orientations were also determined. Other D. nodosus genes were assigned to specific EagI and StuI fragments. Analysis of the resultant map revealed that the putative virulence genes were not clustered on the chromosome which suggests that the D. nodosus virulence determinants have been acquired gradually and that virulence in D. nodosus is an evolving trait.

Functional expression of heterologous type 4 fimbriae in Pseudomonas aeruginosa

Type 4 fimbriae are surface organelles produced by a wide range of bacterial pathogens. In Pseudomonas aeruginosa they are associated with a form of surface translocation known as twitching motility and have also been implicated as the receptor for a number of fimbrial-specific bacteriophages. The infrastructural machinery required for type 4 fimbrial biogenesis appears to be conserved as heterologous subunits from other species can be expressed in P. aeruginosa. All of these studies have, until now, been performed in non-functional Pseudomonas host strains which lack twitching motility. We have constructed isogenic mutants of two commonly studied wild-type P. aeruginosa strains, PAK and PAO1, by replacing the entire pilA gene which encodes the fimbrial subunit. Fimbrial expression and twitching motility were restored by complementation in trans with either the homologous or heterologous subunits from these strains, as well as that from another type 4 fimbriate species, Dichelobacter nodosus. The expression of different subunits allowed us to investigate the precise role that the individual subunit proteins contribute to bacteriophage infection by several fimbrial-specific bacteriophages. Sensitivity to bacteriophages B3cts and D3112cts was restored by the expression of any fimbrial subunit in both PAO1 and PAK cells, indicating that infection by these bacteriophages is fimbrial dependent but not fimbrial specific. In contrast, while sensitivity to the PAK-specific bacteriophage PO4 was restored by the expression of any fimbrial subunit in PAK cells, this did not occur in PAO1 cells except when expressing the PAK subunit. In all cases, the presence of fimbriae was absolutely required to allow a productive bacteriophage infection to occur.

Organization of ribosomal RNA genes from the footrot pathogen Dichelobacter nodosus

Southern hybridization analysis revealed that there were three rrn loci within the genome of Dichelobacter nodosus, the causative organism of ovine footrot. These loci (rrnA, rrnB and rrnC) were isolated on recombinant lambda clones, and comprised 16S, 23S and 5S rRNA genes closely linked in that order. Sequence and primer extension analysis revealed the presence of putative genes encoding tRNA(Ile) and tRNA(Ala) within the 16S-23S spacer region, as well as a number of potential regulatory features. These elements included a single promoter, which was mapped upstream of the 16S rRNA gene and which was similar to Escherichia coli consensus promoter sequences, an AT-rich upstream region, a GC-rich motif that may be involved in stringent control, leader and spacer antitermination sequences, sites for ribonuclease processing, and a putative factor-independent terminator sequence. Potential open reading frames (ORFS) were identified within the regions flanking the rrn loci, with identical copies of the 3' terminal ORF present downstream of each rRNA operon. Determination of the complete sequence of the 5S rRNA gene, and derivation of the 5S rRNA secondary structure, further substantiated the 16S rRNA-based placement of D. nodosus within the gamma division of the Proteobacteria.

Identification of fimbrial assembly genes from Dichelobacter nodosus: evidence that fimP encodes the type-IV prepilin peptidase

Dichelobacter nodosus (Dn) is the causative agent of footrot, an economically significant disease of sheep. One of the factors believed to be involved in the virulence of this organism is its ability to produce type-IV fimbriae, which are the major protective antigens. To investigate the process of fimbrial biogenesis in Dn, gene probes were constructed from pilus biogenesis genes of Pseudomonas aeruginosa (Pa) and used to isolate homologues from Dn. A homologue, designated fimP, of the Pa prepilin peptidase-encoding gene, pilD, was cloned using this approach. The fimP gene product was shown to possess endopeptidase activity when produced in Escherichia coli. Two other fimbrial biogenesis genes fimN and fimO, whose products show similarity to the Pa PilB and PilC proteins, respectively, were identified because of their linkage to fimP. The arrangement of fimN, fimO and fimP in Dn closely resembles the arrangement of pilB, pilC and pilD in Pa.

Molecular cloning of the leuB gene from Bacteroides fragilis by functional complementation in Escherichia coli

Clones containing the Bacteroides fragilis leuB-complementing gene were isolated by screening of a B. fragilis genomic library constructed in Escherichia coli. One recombinant clone, designated pOT865, with the smallest DNA insert (4.5 kb) could complement three independent leuB mutations in E. coli and the leuB-complementing determinant in pOT865 was localized to a region of 1.5-kb DNA. The results of Southern blot analysis suggested that a single copy of the cloned gene was present in the B. fragilis genome. The cloned fragment appeared to contain a sequence that could function as promoter in E. coli and direct the synthesis of a 42-kDa protein. These results suggest that the cloned segment contains the structural gene for beta-isopropylmalate dehydrogenase (leuB).

Characterization and occurrence of two repeated palindromic DNA elements of Brucella spp.: Bru-RS1 and Bru-RS2

Two repeated DNA elements of 103 bp and 105 bp were discovered in brucellae and designated Bru-RS1 and Bru-RS2, respectively. The two elements are palindromic, are 65% similar in sequence, form two families of elements that are slightly divergent in sequence, appear to be intergenic, and are found, collectively, in more than 35 copies in brucellae. These elements are bounded by perfect or nearly perfect inverted repeats. A third copy of the terminal repeat is found within the elements and is the terminus for several truncated copies of the Bru-RS1 family. Hybridization patterns for the elements among brucellae were unique. The elements are dispersed, highly conserved among brucellae, and hot-spots for insertion by IS711.

Development of gene probes of Dichelobacter nodosus for differentiating strains causing virulent, intermediate or benign ovine footrot

Seven Dichelobacter nodosus genomic DNA clones including six specific for virulent and one for benign strains were identified. A collection of 96 footrot isolates, which in turn comprised 27 virulent isolates showing elastase activity at 7 days, 25 high intermediate isolates with elastase activity at 14 days, 24 low intermediate isolates with elastase activity at 21-28 days and 20 benign isolates with no elastase activity at up to 28 days, were used to assess these clones. Of the six virulent specific clones, five (pV238-83, pV405-239, pV470-65, pV470-145 and pV470-178) reacted with 27 virulent isolates, and 12 of 25 high intermediate isolates, but none of 24 low intermediate isolates and 20 benign isolates in dot blot hybridization. The other virulent-specific clone (pV470-13) recognized all 27 virulent and 25 intermediate isolates, and 22 of 24 low intermediate isolates and three of 20 benign isolates in dot blot hybridization. By contrast, the benign-specific clone (pB645-335) detected all 20 benign isolates and 24 low intermediate isolates, and also 13 of 25 high intermediate isolates, but none of 27 virulent isolates in dot blot hybridization. Southern hybridization analysis indicated that whereas clones pV238-83, pV405-239 and pV470-178 bound a Sau3A band of 0.5 kb, clones pV470-65 and pV470-145 recognized two Sau3A bands of 0.7 and 0.5 kb in virulent strains of serogroups A to I. However, clone pV470-13 detected a Sau3A band pattern in virulent strains different from those recognized by the other five virulent specific-clones. Besides showing a distinct Sau3A band pattern in intermediate strains, pV470-13 also reacted with three benign strains that showed binding with it in dot blot hybridization. The benign-specific clone pV645-335 detected a Sau3A band of 0.5 kb in both intermediate and benign strains of serogroups A to I. Thus the combination of pV470-13 and pB645-335, or any other virulent-specific clone, would clearly differentiate among D. nodosus strains causing virulent, intermediate or benign footrot.

Genetic organization of the duplicated vap region of the Dichelobacter nodosus genome

The recombinant plasmid pJIR318 contains a fragment of the Dichelobacter nodosus genome which is associated with virulence. Sequence analysis of the pJIR318 insert has shown that it contains four vap (virulence-associated protein) genes which are homologous to open reading frames found on the Escherichia coli F plasmid and the Neisseria gonorrhoeae cryptic plasmid (M. E. Katz, R. A. Strugnell, and J. I. Rood, Infect. and Immun. 60:4586-4592, 1992). The plasmid pJIR318 hybridizes to three regions of the D. nodosus genome, each of which has now been isolated. Regions 1 and 3 were found to be adjacent in the genome of D. nodosus A198, and the order of the vap genes in vap regions 1 and 2 were shown to be identical. Partial sequence analysis and Southern blot analysis of the vap regions showed that the three regions probably arose by a duplication event(s) followed by insertions and/or deletions. A recombinant plasmid, pJIR749, was isolated from a library of a benign D. nodosus strain, 305. This plasmid contained sequences from both ends of vap region 2. Analysis of pJIR749 showed that the sequences on either side of vap region 2 were separated by 324 bp in the genome of benign strain 305 and that the orientations of the sequences were different. It is clear that a simple insertion or deletion event did not generate the benign and virulent strains studied. A model which describes the evolution of the duplicated vap regions in D. nodosus A198 is presented.

Dichelobacter nodosus: differentiation of virulent and benign strains by gene probe based dot blot hybridisation

Gene probes specific for benign and virulent strains of Dichelobacter nodosus were used in a dot blot hybridisation procedure involving 96 strains of D. nodosus isolated from cases of ovine footrot. The performance of the probes was compared with that of the elastase test. All 27 strains with elastase activity at 7 days and 12 of 25 strains with elastase activity at 14 days reacted with the virulent-specific probe. Twenty-four strains with elastase activity between 21-28 days, and 20 strains with negative elastase activity up to 28 days did not bind with this probe. On the other hand, the benign-specific probe failed to bind with the 27 strains with elastase activity at 7 days, and 13 of the 25 strains with elastase activity at 14 days but reacted with 20 of the 24 strains with elastase activity at 21-28 days, and 19 of the 20 strains with negative elastase activity up to 28 days. The 12 strains with elastase activity at 14 days which were detected by the virulent-specific probe were not those recognised by the benign-specific probe. The use of virulent and benign specific gene probes in combination provides a rapid and precise screening system for differentiation of virulent and higher intermediate footrot from benign and lower intermediate footrot.

Recombinant vaccines against ovine footrot

For the past 20 years footrot vaccines have evolved from simple bacterins to highly specific recombinant DNA (rDNA) fimbrial vaccines. The development of these vaccines has left a trail of discoveries, challenges and solutions; these processes continue as we move closer to understanding the requirements of a footrot vaccine. The initial whole cell vaccines were unsuccessful due to the short duration of immunity and incorporation of limited serotypes. A multistrain vaccine eliminated the problem of serotype inclusion, although the duration of immunity in many cases is still inadequate. The proteases of Dichelobacter nodosus appear to be cross protective; however, little is known of their ability to protect sheep against footrot. The major protective immunogen is the bacterial fimbriae, which also forms the basis for the K-agglutination serotyping system. K-agglutinin titre correlates directly with resistance to challenge. The protective fimbrial epitope is conformationally dependent, suggesting little advantage in the development of synthetic peptide vaccines. To enhance the efficiency of vaccine production D. nodosus fimbrial genes were eventually cloned and successfully expressed in Ps. aeruginosa. Monovalent vaccines based on recombinant fimbriae are omnipotent, inducing high levels of agglutinins and long lasting immunity. In multivalent vaccines, on the other hand, incorporation of each additional serogroup into the vaccine results in reduced efficacy both in terms of reduced K-agglutinin titres and reduced protection following challenge. The least effective are multivalent formulations representing all major serogroups. In addition, considerable genetic variation has been observed in the ability of sheep to respond optimally to each serogroup in a multivalent vaccine. Results show that the limitation of the sheep to mount an effective immune response, rather than the quality or quantity of the immunogen, limits the efficacy of current footrot vaccines. Studies are being undertaken to examine in detail the immune response of sheep to potentially highly effective footrot vaccines.

Detection of Dichelobacter nodosus using species-specific oligonucleotides as PCR primers

Dichelobacter nodosus is an essential causative agent of ovine footrot, a disease of major economic significance. Four oligonucleotides complementary to variable regions of the 16S rRNA of D. nodosus were identified, synthesized and tested for their specificity and sensitivity as probes for the detection of D. nodosus. In hybridization reactions using total RNA as the target nucleic acid, three probes were found to be both sensitive and species-specific. When these probes were used as primers in PCR reactions, on both purified D. nodosus DNA and whole cells, the sensitivity of detection was increased by several orders of magnitude. Using PCR, it was possible to detect the presence of D. nodosus by direct examination of lesion material from footrot infected sheep.

Amplification fragment length polymorphism in Brucella strains by use of polymerase chain reaction with arbitrary primers

DNA heterogeneity among members of the genus Brucella was demonstrated with the arbitrarily primed polymerase chain reaction (AP-PCR). Simple, reproducible genomic fingerprints from DNA of 25 different Brucella strains were generated with five arbitrarily chosen primers, alone and in pairs, with the PCR. Reaction conditions were optimized for each primer. Several DNA segments were amplified in each sample with all of the primers. PCR products that are not shared among all strains act as polymorphic markers. Polymorphism was apparent for each primer. The Brucella strains can be distinguished according to the banding patterns of their amplified DNA on agarose gels, and the differences can be diagnostic of specific strains. To determine genetic relatedness among the Brucella strains, similarity coefficients were calculated. Statistical analysis of the similarity coefficients revealed the degrees of relatedness among strains of the genus Brucella.

Production of Neisseria gonorrhoeae pili (fimbriae) in Pseudomonas aeruginosa

Pseudomonas aeruginosa K/2PfS, when transformed with an expression plasmid harboring the pilin gene (pilE1) of Neisseria gonorrhoeae MS11, was able to express and assemble gonococcal pilin monomers into surface-associated pili, as judged by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, immunoblotting, and immunoelectron microscopy. Concomitant with the expression of gonococcal pili in P. aeruginosa was the virtual loss of production of P. aeruginosa K/2PfS pili normally associated with the host cell.

Molecular characterization of a genomic region associated with virulence in Dichelobacter nodosus

The major pathogen implicated in footrot, a highly contagious disease of sheep, is the strict anaerobe Dichelobacter nodosus (formerly Bacteroides nodosus). Sequence analysis of a 2,262-bp segment of the D. nodosus genome which is more prevalent in virulent isolates than in other isolates showed the presence of four open reading frames which appeared to have consensus transcriptional and translational start signals. These virulence-associated genes have been designated vapABCD. Two of the three copies of the vap region in the genome of the reference strain D. nodosus A198 were shown to carry all of the vap genes, whereas one copy contained only the vapD gene. The VapD protein was gel purified, shown to contain the predicted amino-terminal sequence, and used to raise rabbit antibodies. Western blots (immunoblots) showed that all of the D. nodosus strains tested that contained the vap region produced the VapD protein. The VapD protein had significant amino acid sequence identity with open reading frame 5 from the cryptic plasmid of Neisseria gonorrhoeae, and the vapBC operon had sequence similarity with the trbH region of the Escherichia coli F plasmid. It is proposed that these gene regions evolved from the integration of a conjugative plasmid from another bacterial species into the D. nodosus chromosome.

Sequence of fimbrial subunit-encoding genes from virulent and benign isolates of Dichelobacter (Bacteroides) nodosus

Both virulent and benign isolates of the ovine pathogen Dichelobacter (Bacteroides) nodosus produce polar fimbriae which have been implicated in twitching motility. The fimbrial subunit-encoding genes from two virulent and two benign serogroup-B isolates of D. nodosus were cloned and sequenced. Analysis of the deduced amino acid (aa) sequences of these subunits indicated the presence of substitutions that appeared to correlate with the virulence phenotype. However, these aa substitutions were located in variable regions of the protein where they are unlikely to alter the functional properties of the fimbriae. The aa sequences of the serogroup-B subunits had a very high level (91-95%) of similarity, particularly at the N terminus, where the conserved region extended up to aa 61. Specific aa substitutions within the subunit of one isolate may reflect its serotypic variation from the other serogroup-B subunits studied.

Organization of the fimbrial gene region of Bacteroides nodosus: class I and class II strains

The fimbrial subunit genes of Bacteroides nodosus may be divided into two distinct classes, based on the sequence of the major subunit gene fimA (accompanying paper--Mattick et al., 1991). The genetic organization of the fibrial gene region in these two classes is also distinct. Upstream of fimA in both classes in opposite transcriptional orientation is the gene aroA which encodes amino acid biosynthetic enzyme 5-enolpyruvylshikimate-3-phosphate synthase. However, downstream of fimA the two classes are quite different until homology is restored at a bidirectional transcription termination signal separating the fimbrial operon from a gene clpB, which appears to encode the regulatory subunit of an ATP-dependent protease. Between aroA and clpB class I strains contain, apart from fimA, only one other gene (fimB). Sequence and polymerase chain reaction analyses indicate that fimB does not have a separate promoter but rather is co-transcribed with fimA at a level attenuated by the strength of the transcription termination signal in the intergenic region. In class II strains fimA is followed by a more extended region containing three genes, which appear to have the same transcriptional arrangement as fimB. The second of these genes (fimD) may represent a functional analogue of fimB although there is no close sequence homology. The first gene (fimC) has no obvious similarity to either fimB or fimD. Beyond fimD, at the 3' end of the class II-specific region, is a variant fimbrial subunit gene (fimZ) which is virtually identical in serogroups D and H and which appears to represent a duplicate, possibly redundant, gene closely related to the progenitor of the more divergent structural subunit fimA gene found in these strains. Comparisons of the predicted fimZ product with those of fimA in class I and class II strains, as well as of the boundaries of the class-specific regions, suggest that the class II sequences evolved in another type 4 fimbriate species and were subsequently substituted in the B. nodosus genome by lateral transfer. Analysis of the sequences flanking fimA in different strains indicates that recombinational exchange of both fimA and the entire operon has also occurred between strains, and is possibly a mechanism for disseminating structural diversity in the population.

Gene sequences and comparison of the fimbrial subunits representative of Bacteroides nodosus serotypes A to I: class I and class II strains

We have determined the nucleotide sequences of the genes encoding the fimbrial subunits representative of the known Bacteroides nodosus serogroups. All of the genes are preceded by a highly conserved region which includes the likely promoter and transcriptional regulator sites as well as the ribosome-biding site, and are followed within a short but variable distance by a sequence with the characteristics of a transcription termination or attenuation signal. Based on sequence and organization, the subunits can be divided into two major classes called I (serogroups A, B, C, E, F, G, and I) and II (serogroups D and H). All contain the same seven-amino-acid positively charged leader sequence and conserved hydrophobic amino-terminal sequence typical of type 4 fibriae. Beyond this point the class II subunits are quite different from class I and share features more in common with those from other type 4 fimbriate bacteria, such as Moraxella bovis and Pseudomonas aeruginosa. The larger class I may be further subdivided into two subsets: (i) [A, E, F)(B, I)) and (ii) (C, G). These proteins exhibit three major clusters of variation, at either end of the presumptive disulphide loop which spans the central third of the protein, and near the carboxy-terimus, with dispersed changes in between. The length of the mature subunits varies from 152-156 amino acids, and the variation includes small insertions or deletions in the variable clusters between more conserved domains. The class II subunits are 149 amino acids in length and contain two pairs of cysteine residues: one is at the end of the amino-terminal conserved region, and the other is at the end of the protein. The major variation occurs in the central region of the molecule, and again small insertions or deletions are required to align adjacent conserved domains. There is also a striking absence of silent codon changes in the 5' coding region of all of these genes, indicating that these sequences have a secondary genetic function, probably in recombinational exchange.

Polymorphism in Brucella spp. due to highly repeated DNA

The species of Brucella are very closely related, but Brucella ovis does not express detectable amounts of a protein, designated BCSP31, that is common to the other species. We studied the lack of expression of BCSP31 by Southern analysis. DNAs from the B. ovis culture collection strains and field isolates were probed with a 1.3-kb HindIII fragment encoding BCSP31 of Brucella abortus. The probe hybridized to a 1.6-kb HindIII fragment of all B. ovis strains tested, showing that the gene is present in B. ovis but occurs on a larger restriction fragment. DNA linkage studies and restriction mapping of the cloned polymorphic region of B. ovis showed that the polymorphism was due to a DNA insertion of approximately 0.9 kb at a site downstream of the BCSP31-coding region. When the 1.6-kb polymorphic B. ovis fragment was used to probe a HindIII Southern blot of cellular DNA of strains of B. ovis and of B. abortus, at least 24 fragments of B. ovis and 6 fragments of B. abortus hybridized to the inserted DNA. Specimens of B. ovis collected over a 30-year period on two continents had similar hybridization patterns. The large difference between B. ovis and B. abortus in the number of copies of the repeated DNA is interesting in the context of the closeness of the Brucella species.

The RNA polymerases of Porphyromonas gingivalis and Fusobacterium nucleatum are unrelated to the RNA polymerase of Escherichia coli

Western blot analysis that used antisera to the E. coli core enzyme and sigma factors was used for examination of the RNA polymerase of Actinobacillus actinomycetemcomitans, Streptococcus mutans, Fusobacterium nucleatum, and Porphyromonas gingivalis. Both antisera reacted with proteins in A. actinomycetemcomitans and S. mutans whole-cell extracts. Reactions were seen with some F. nucleatum proteins when the anti-core RNA polymerase antisera were used, but the cross-reacting proteins were not of an expected molecular weight for beta or beta'. No reaction with F. nucleatum proteins was seen when extracts were reacted with antisera to E. coli sigma factor. There were no cross-reacting proteins detected in P. gingivalis extracts with either antisera. These results suggest that E. coli RNA polymerase may not be sufficiently similar to P. gingivalis and F. nucleatum RNA polymerase for E. coli RNA polymerase to recognize P. gingivalis or F. nucleatum promoters. Partially purified P. gingivalis and F. nucleatum RNA polymerase exhibited a specificity for a P. gingivalis DNA template, while having a decreased activity from an E. coli DNA template. The antibiotic sensitivity profile of P. gingivalis and F. nucleatum RNA polymerase activity was shown to differ from that of E. coli, with these activities not being affected by rifampicin, streptovaricin, or streptolydigin. We conclude that the efficient cloning and expression of P. gingivalis and F. nucleatum genes in E. coli will require the use of promoter-containing expression vectors.

Expression and regulation of a Bacteroides fragilis sucrose utilization system cloned in Escherichia coli

A Bacteroides fragilis strain isolated from human feces was the source of chromosomal DNA in the construction of plasmid pBS100. The cloned 6-kilobase insert of plasmid pBS100 conferred a sucrose positivity phenotype on transformed cells of Escherichia coli JA221. E. coli JA221(pBS100) cells were able to utilize sucrose as the sole source of carbon because of the presence of sucrase enzyme and sucrose uptake activities. Sucrase activity was inducible in B. fragilis but constitutive in E. coli JA221(pBS100) cells. In sucrose-minimal medium, both B. fragilis and E. coli JA221(pBS100) produced intracellular and extracellular sucrase activities throughout the growth cycle. Osmotic shock experiments performed on E. coli JA221(pBS100) indicated that up to 55% of the sucrase activity was localized in the periplasmic space, 30% was in the cytoplasm, and the remaining 15% was in the cell-free extracellular supernatant fluid. B. fragilis and E. coli JA221(pBS100) actively transported sucrose. Sucrose uptake was induced by sucrose in B. fragilis, whereas the uptake activity in E. coli JA221(pBS100) was constitutive. E. coli JA221(pBS100) appeared to transport sucrose by a phosphotransferase-independent system. B. fragilis transported sucrose only under strictly anaerobic conditions. No uptake activity was detected under aerobic conditions with or without addition of catalase.

Morphogenetic expression of Moraxella bovis fimbriae (pili) in Pseudomonas aeruginosa

Type 4 fimbriae (pili) are found in a wide variety of gram-negative bacteria and are composed of small structural subunits which share significant sequence homology among different species, especially at their amino-terminal ends. Previous studies demonstrating morphogenetic expression of Bacteroides nodosus fimbriae from cloned subunit genes in Pseudomonas aeruginosa suggested that there is a common mechanism for type 4 fimbriae assembly and that the structural subunits are interchangeable (J. S. Mattick et al., J. Bacteriol. 169:33-41, 1987). Here we have examined the expression of Moraxella bovis fimbrial subunits in P. aeruginosa. M. bovis subunits were assembled into extracellular fimbriae in this host, in some cases as a homopolymer but in others as a mosaic with the indigenous subunit, indicating structural equivalence. This result contrasts with other studies in which recombinant P. aeruginosa expressing different subunits produced fimbriae composed almost exclusively of one subunit or the other (T. C. Elleman and J. E. Peterson, Mol. Microbiol. 1:377-380, 1987). Both observations can be explained by reversibility of subunit-subunit interactions at the site of assembly, with the forward equilibrium favoring chain extension between compatible subunits.

Identification and genetic mapping of proteins encoded in the fimbrial subunit gene region of Bacteroides nodosus

The fimbriae produced by the anaerobic bacterium Bacteroides nodosus are important in the pathogenesis of ovine foot rot. Studies on other microorganisms have shown that the genes coding for the production and assembly of fimbriae are often clustered. By the use of maxicells, transposon mutagenesis and expression vectors, we have identified several genes which are located in the fimbrial subunit gene region. Antiserum was prepared against one of the proteins (88 kDa) which we were able to overproduce in Escherichia coli. In Western blots, these antibodies reacted with an 88 kDa protein located in the B. nodosus cell membrane. However, they did not react with the putative basal protein which is found in fimbrial preparations. We concluded that in B. nodosus the genes involved in fimbrial assembly are not all localised to one small region of the genome. In addition, our studies showed that although the fimbrial subunits are not assembled into intact fimbriae, an N-terminal sequence is processed in E. coli.

Molecular analysis of one of multiple protease-encoding genes from the prototype virulent strain of Bacteroides nodosus

The aim of these studies was to examine the organization of the Bacteroides nodosus protease-encoding gene(s). The extracellular serine proteases (38 kDa) from the prototype virulent strain of B. nodosus were purified and used to raise a specific antiserum in rabbits. This antiserum was used in a colony immunoassay to screen a genomic DNA library constructed in Escherichia coli using BamHI-digested B. nodosus DNA and the plasmid pBR322. An E. coli clone expressing a 50-kDa immunoreactive polypeptide was identified. No protease activity was detected in the culture media, or in crude soluble and membrane fractions prepared from this clone. Restriction mapping and deletion analysis of the recombinant plasmid, pEKM2, was used to locate the coding region to a 1.4-kb EcoRI-BamHI fragment which was subsequently sequenced. A large open reading frame was found to extend through the BamHI site from a putative start codon just downstream from the EcoRI site, which indicated that the complete gene was not isolated. Southern blotting demonstrated that there were at least three B. nodosus BamHI fragments which were homologous to the 0.4-kb PstI-BamHI fragment of pEKM2. Based on these results the existence of multiple protease genes in B. nodosus was postulated.

Cloning and expression of a Salmonella enteritidis fimbrin gene in Escherichia coli

A gene bank of DNA from a human isolate of Salmonella enteritidis was constructed in the cosmid pHC79 in Escherichia coli HB101. Five clones containing 35- to 45-kilobase inserts of S. enteritidis DNA reacted in colony immunoblot assays with a polyclonal antiserum prepared against purified S. enteritidis fimbriae. Electron microscopy showed that none of the five fimbrin-producing clones produced fimbriae, yet radioimmunoprecipitation and sodium dodecyl sulfate-polyacrylamide gel electrophoresis located the 14,400-molecular-weight S. enteritidis in the outer membrane fraction of three of the clones and in the periplasmic fraction of all five clones. By using an oligonucleotide probe homologous to the 5' region of the fimbrin structural gene, the fimbrin gene was located on a 5.3-kilobase HindIII fragment. In vitro transcription-translation analysis verified that this HindIII fragment subcloned into plasmid pTZ18R produced unprocessed S. enteritidis fimbrin of molecular weight 16,400. Dot blot hybridization against a selection of strains of the family Enterobacteriaceae indicated a limited distribution of the S. enteritidis fimbrin gene.

Pilin-gene phase variation of Moraxella bovis is caused by an inversion of the pilin genes

Moraxella bovis Epp63 can express either of two different pilin proteins, called alpha and beta. We have previously cloned and sequenced the beta-pilin gene and now report that DNAs isolated from bacteria expressing alpha pilin have hybridization patterns consistently different from those of bacteria expressing beta pilin. The phase variation between alpha- and beta-pilin gene expression appears to be associated with an inversion of about 2 kilobases of DNA, whose endpoints occur within the coding region of the expressed pilin gene. Comparisons of the beta-pilin gene sequence with those of well-studied bacterial inversion systems revealed a stretch of 58% sequence similarity (21 of 36 base pairs) between the left inverted repeat of the Salmonella typhimurium flagellar hin control region and the amino-terminal portion of the beta-pilin gene.

Protection of sheep against footrot with a recombinant DNA-based fimbrial vaccine

Recombinant Pseudomonas aeruginosa cells containing the Bacteroides nodosus fimbrial subunit gene under the transcriptional control of a strong promoter produce large amounts of B. nodosus-type fimbriae. We have carried out vaccination trials which show that these fimbriae are just as effective as either natural fimbriae or whole cell preparations of B. nodosus in inducing protective immunity against homologous footrot challenge. The recombinant-produced fimbriae are also effective therapeutically in accelerating the rate of healing of pre-existing footrot lesions. These results confirm that the structural subunit of the fimbrial strand is a primary protective antigen against footrot, and demonstrate the practicality and potential of recombinant DNA approaches to the development of new vaccines against B. nodosus and other Type 4 fimbriate pathogens.

Mapping of export signals of Pseudomonas aeruginosa pilin with alkaline phosphatase fusions

Pili of Pseudomonas aeruginosa are assembled from monomers of the structural subunit, pilin, after secretion of this protein across the bacterial membrane. These subunits are initally synthesized as precursors (prepilin) with a six-amino-acid leader peptide that is cleaved off during or after membrane traversal, followed by methylation of the amino-terminal phenylalanine residue. This report demonstrates that additional sequences from the N terminus of the mature protein are necessary for membrane translocation. Gene fusions were made between amino-terminal coding sequences of the cloned pilin gene (pilA) and the structural gene for Escherichia coli alkaline phosphatase (phoA) devoid of a signal sequence. Fusions between at least 45 amino acid residues of the mature pilin and alkaline phosphatase resulted in translocation of the fusion proteins across the cytoplasmic membranes of both P. aeruginosa and E. coli strains carrying recombinant plasmids, as measured by alkaline phosphatase activity and Western blotting. Fusion proteins constructed with the first 10 amino acids of prepilin (including the 6-amino-acid leader peptide) were not secreted, although they were detected in the cytoplasm. Therefore, unlike that of the majority of secreted proteins that are synthesized with transient signal sequences, the membrane traversal of pilin across the bacterial membrane requires the transient six-amino-acid leader peptide as well as sequences contained in the N-terminal region of the mature pilin protein.

Recent advances in Bacteroides genetics

Bacteroides are Gram-negative, obligate anaerobes that are present in high concentrations within the intestinal tracts of humans and animals. Bacteroides are also important opportunistic pathogens of humans and animals. Methods for genetic manipulation of these important organisms have only recently begun to emerge. Shuttle vectors which can be transferred by conjugation between Escherichia coli to Bacteroides are now available. A method for transforming some strains of Bacteroides has been developed. Two Bacteroides transposons, Tn4351 and Tn4400, have been found and one of them, Tn4351, has been used for transposon mutagenesis of Bacteroides. Several different Bacteroides genes have now been cloned, including a gene that codes for resistance to clindamycin, genes that code for polysaccharidases (chondroitin lyase and pullulanase), and a gene that codes for a fimbrial subunit. These cloned genes have been used to study the organization and regulation of Bacteroides genes.

Morphogenetic expression of Bacteroides nodosus fimbriae in Pseudomonas aeruginosa

Type 4 fimbriae are found in a range of pathogenic bacteria, including Bacteroides nodosus, Moraxella bovis, Neisseria gonorrhoeae, and Pseudomonas aeruginosa. The structural subunits of these fimbriae all contain a highly conserved hydrophobic amino-terminal sequence preceding a variable hydrophilic carboxy-terminal region. We show here that recombinant P. aeruginosa cells containing the B. nodosus fimbrial subunit gene under the control of a strong promoter (pL, from bacteriophage lambda) produced large amounts of fimbriae that were structurally and antigenically indistinguishable from those produced by B. nodosus. This was demonstrated by fimbrial isolation and purification, electrophoretic and Western transfer analyses, and immunogold labeling and electron microscopy. These results suggest that type 4 fimbriated bacteria use a common mechanism for fimbrial assembly and that the structural subunits are interchangeable, thereby providing a basis for the development of multivalent vaccines.

Complete nucleotide sequence and transcription of ermF, a macrolide-lincosamide-streptogramin B resistance determinant from Bacteroides fragilis

DNA sequence analysis of a portion of an EcoRI fragment of the Bacteroides fragilis R plasmid pBF4 has allowed us to identify the macrolide-lincosamide-streptogramin B resistance (MLSr) gene, ermF. ermF had a relative moles percent G + C of 32, was 798 base pairs in length, and encoded a protein of approximately 30,360 daltons. Comparison between the deduced amino acid sequence of ermF and six other erm genes from gram-positive bacteria revealed striking homologies among all of these determinants, suggesting a common origin. Based on these and other data, we believe that ermF codes for an rRNA methylase. Analysis of the nucleotide sequences upstream and downstream from the ermF gene revealed the presence of directly repeated sequences, now identified as two copies of the insertion element IS4351. One of these insertion elements was only 26 base pairs from the start codon of ermF and contained the transcriptional start signal for this gene as judged by S1 nuclease mapping experiments. Additional sequence analysis of the 26 base pairs separating ermF and IS4351 disclosed strong similarities between this region and the upstream regulatory control sequences of ermC and ermA (determinants of staphylococcal origin). These results suggested that ermF was not of Bacteroides origin and are discussed in terms of the evolution of ermF and the expression of drug resistance in heterologous hosts.

Expression of the Pseudomonas aeruginosa PAK pilin gene in Escherichia coli

Pseudomonas aeruginosa is a piliated opportunistic pathogen. We have recently reported the cloning of the structural gene for the pilus protein, pilin, from P. aeruginosa PAK (B. L. Pasloske, B. B. Finlay, and W. Paranchych, FEBS Lett. 183:408-412, 1985), and in this paper we present evidence that this chimera (pBP001) expresses P. aeruginosa PAK pilin in Escherichia coli independent of a vector promoter. The strength of the promoter for the PAK pilin gene was assayed, and the cellular location of the pilin protein within E. coli was examined. This protein was present mainly in the inner membrane fraction both with and without its six-amino-acid leader sequence, but it was not assembled into pili.

Cloning and expression of the pilin gene of Pseudomonas aeruginosa PAK in Escherichia coli

Many strains of Pseudomonas aeruginosa possess pili which have been implicated in the pathogenesis of the organism. This report presents the cloning and expression in Escherichia coli of the gene encoding the structural subunit of the pili of P. aeruginosa PAK. Total DNA from this strain was partially digested with Sau3A and inserted into the cloning vector pUC18. Recombinant E. coli clones were screened with oligonucleotide probes prepared from the constant region of the previously published amino acid sequence of the mature pilin subunit. Several positive clones were identified, and restriction maps were generated. Each clone contained an identical 1.1-kilobase HindIII fragment which hybridized to the oligonucleotide probes. Western blot analysis showed that all of the clones expressed small amounts of the P. aeruginosa pilin subunit, which has a molecular mass of ca. 18,000. This expression occurred independently of the orientation of the inserted DNA fragments in the cloning vector, indicating that synthesis was directed from an internal promoter. However, subclones containing the 1.1-kilobase HindIII fragment in a specific orientation produced an order of magnitude more of the pilin subunit. While the expressed pilin antigen was located in both the cytoplasmic and outer membrane fractions of E. coli, none appeared to be polymerized into a pilus structure.

Expression of the pilin gene from Bacteroides nodosus in Escherichia coli

Bacterial plasmids that direct the expression in Escherichia coli of the pilin of Bacteroides nodosus were constructed. The quantity of pilin produced was greater than that of the pilin synthesized by B. nodosus, but no surface structural pili were present; pilin was found associated with the inner membrane of E. coli. Vaccination of sheep with E. coli containing pilin elicited increases in agglutinating and enzyme-linked immunosorbent assay antibody titers, which in turn were lower than the titers in sheep immunized with pilin from B. nodosus. The E. coli-produced pilin vaccine initially appeared to delay the progression of infection in immunized sheep after a challenge with virulent homologous B. nodosus, but at a later time the severity of foot rot was similar to that in sheep vaccinated with a placebo.

Cloning and expression in Escherichia coli of a gene coding for a chondroitin lyase from Bacteroides thetaiotaomicron

We cloned the gene for one of the two chondroitin lyases of Bacteroides thetaiotaomicron into the cosmid vector pHC79 and subcloned it into pBR328. No proteins the size of B. thetaiotaomicron chondroitin lyase I or II (104 to 108 kilodaltons) were detectable in maxicell or in vitro transcription-translation preparations. However, partial purification of the chondroitin lyase activity from the Escherichia coli subclone showed that its properties were similar to those of the B. thetaiotaomicron chondroitin lyases. Antibodies to the chondroitin lyase that was produced in E. coli cross-reacted with the B. thetaiotaomicron chondroitin lyase II but not with chondroitin lyase I. The molecular weight of the enzyme produced in E. coli, as measured by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and by gel filtration, was slightly lower than those of the two chondroitin lyases from B. thetaiotaomicron; the enzyme had a higher affinity for bacterial membranes and for heparin-agarose, and cyanogen bromide digestion products of the chondroitin lyase produced in E. coli differed slightly from those of B. thetaiotaomicron chondroitin lyase II. gamma delta mutagenesis was used to locate the chondroitin lyase gene on the subcloned 7.8-kilobase EcoRI fragment. The size of the gene was approximately 3.3 kilobases, as expected for a protein with a molecular weight of 104,000.

Cloning and sequencing of a Moraxella bovis pilin gene

Moraxella bovis pili have been shown to play a major role in both infectivity and protective immunity of bovine infectious keratoconjunctivitis. Sonicated M. bovis DNA from the piliated strain EPP63 was inserted into the vector lambda gt11 with EcoRI linkers. Recombinant phage were screened with an oligonucleotide probe based on the amino-terminal portion of the DNA sequence of a Neisseria gonorrhoeae pilin gene. Two candidate phages produced a protein that comigrated with EPP63 beta pilin in sodium dodecyl sulfate-polyacrylamide gels and bound anti-pilus antisera. The 1.9-kilobase insert from one of these, lambda gt11M182, was subcloned in both orientations into pBR322, forming the plasmids pMxB7 and pMxB9, both of which produced beta pilin, as did pMxB12, a HindIII deletion derivative of pMxB7. In HB101(pMxB12), the M. bovis pilin protein was shown to be primarily localized in the inner membrane. The entire 939-base-pair insert of pMxB12 was sequenced, revealing a ribosome binding site just upstream of the coding region and an AT-rich region further upstream containing some potential RNA polymerase recognition sites. The translation of the sequence predicts a six-amino-acid leader sequence preceding the phenylalanine that begins the mature protein. Codon usage analysis of the M. bovis beta pilin gene revealed greater use of the CUA codon for leucine than usual for a well-expressed Escherichia coli gene. Comparisons of the M. bovis EPP63 beta pilin protein sequence with other pilin gene sequences are presented.