Molecular cloning, nucleotide sequence, and characterization of lppB, encoding an antigenic 40-kilodalton lipoprotein of Haemophilus somnus

Cattle Immunized with a Recombinant Subunit Vaccine Formulation Exhibits a Trend towards Protection against Histophilus somni Bacterial Challenge

Histophilosis, a mucosal and septicemic infection of cattle is caused by the Gram negative pathogen Histophilus somni (H. somni). As existing vaccines against H. somni infection have shown to be of limited efficacy, we used a reverse vaccinology approach to identify new vaccine candidates. Three groups (B, C, D) of cattle were immunized with subunit vaccines and a control group (group A) was vaccinated with adjuvant alone. All four groups were challenged with H. somni. The results demonstrate that there was no significant difference in clinical signs, joint lesions, weight change or rectal temperature between any of the vaccinated groups (B,C,D) vs the control group A. However, the trend to protection was greatest for group C vaccinates. The group C vaccine was a pool of six recombinant proteins. Serum antibody responses determined using ELISA showed significantly higher titers for group C, with P values ranging from < 0.0148 to < 0.0002, than group A. Even though serum antibody titers in group B (5 out of 6 antigens) and group D were significantly higher compared to group A, they exerted less of a trend towards protection. In conclusion, the vaccine used in group C exhibits a trend towards protective immunity in cattle and would be a good candidate for further analysis to determine which proteins were responsible for the trend towards protection.

Reverse vaccinology as an approach for developing Histophilus somni vaccine candidates

Histophilosis of cattle is caused by the Gram negative bacterial pathogen Histophilus somni (H. somni) which is also associated with the bovine respiratory disease (BRD) complex. Existing vaccines for H. somni include either killed cells or bacteria-free outer membrane proteins from the organism which have proven to be moderately successful. In this study, reverse vaccinology was used to predict potential H. somni vaccine candidates from genome sequences. In turn, these may protect animals against new strains circulating in the field. Whole genome sequencing of six recent clinical H. somni isolates was performed using an Illumina MiSeq and compared to six genomes from the 1980's. De novo assembly of crude whole genomes was completed using Geneious 6.1.7. Protein coding regions was predicted using Glimmer3. Scores from multiple web-based programs were utilized to evaluate the antigenicity of these predicted proteins which were finally ranked based on their surface exposure scores. A single new strain was selected for future vaccine development based on conservation of the protein candidates among all 12 isolates. A positive signal with convalescent serum for these antigens in western blots indicates in vivo recognition. In order to test the protective capacity of these antigens bovine animal trials are ongoing.

Two outer membrane lipoproteins from Histophilus somni are immunogenic in rabbits and sheep and induce protection against bacterial challenge in mice

Histophilus somni is an economically important pathogen of cattle and other ruminants and is considered one of the key components of the bovine respiratory disease (BRD) complex, the leading cause of economic loss in the livestock industry. BRD is a multifactorial syndrome, in which a triad of agents, including bacteria, viruses, and predisposing factors or "stressors," combines to induce disease. Although vaccines against H. somni have been used for many decades, traditional bacterins have failed to demonstrate effective protection in vaccinated animals. Hence, the BRD complex continues to produce strong adverse effects on the health and well-being of stock and feeder cattle. The generation of recombinant proteins may facilitate the development of more effective vaccines against H. somni, which could confer better protection against BRD. In the present study, primers were designed to amplify, clone, express, and purify two recombinant lipoproteins from H. somni, p31 (Plp4) and p40 (LppB), which are structural proteins of the outer bacterial membrane. The results presented here demonstrate, to our knowledge for the first time, that when formulated, an experimental vaccine enriched with these two recombinant lipoproteins generates high antibody titers in rabbits and sheep and exerts a protective effect in mice against septicemia induced by H. somni bacterial challenge.

Role of Rhizobium endoglucanase CelC2 in cellulose biosynthesis and biofilm formation on plant roots and abiotic surfaces

Background

The synthesis of cellulose is among the most important but poorly understood biochemical processes, especially in bacteria, due to its complexity and high degree of regulation. In this study, we analyzed both the production of cellulose by all known members of the Rhizobiaceae and the diversity of Rhizobium celABC operon predicted to be involved in cellulose biosynthesis. We also investigated the involvement in cellulose production and biofilm formation of celC gene encoding an endoglucanase (CelC2) that is required for canonical symbiotic root hair infection by Rhizobium leguminosarum bv. trifolii.

Results

ANU843 celC mutants lacking (ANU843ΔC2) or overproducing cellulase (ANU843C2⁺) produced greatly increased or reduced amounts of external cellulose micro fibrils, respectively. Calcofluor-stained cellulose micro fibrils were considerably longer when formed by ANU843ΔC2 bacteria rather than by the wild-type strain, in correlation with a significant increase in their flocculation in batch culture. In contrast, neither calcofluor-stained extracellular micro fibrils nor flocculation was detectable in ANU843C2⁺ cells. To clarify the role of cellulose synthesis in Rhizobium cell aggregation and attachment, we analyzed the ability of these mutants to produce biofilms on different surfaces. Alteration of wild-type CelC2 levels resulted in a reduced ability of bacteria to form biofilms both in abiotic surfaces and in planta.

Conclusions

Our results support a key role of the CelC2 cellulase in cellulose biosynthesis by modulating the length of the cellulose fibrils that mediate firm adhesion among Rhizobium bacteria leading to biofilm formation. Rhizobium cellulose is an essential component of the biofilm polysaccharidic matrix architecture and either an excess or a defect of this “building material” seem to collapse the biofilm structure. These results position cellulose hydrolytic enzymes as excellent anti-biofilm candidates.

Immunoproteomic analysis of outer membrane proteins and extracellular proteins of Actinobacillus pleuropneumoniae JL03 serotype 3

Background

Actinobacillus pleuropneumoniae is the causative agent of porcine contagious pleuropneumonia, a highly contagious respiratory infection in pigs, and all the 15 serotypes are able to cause disease. Current vaccines including subunit vaccines could not provide satisfactory protection against A. pleuropneumoniae. In this study, the immunoproteomic approach was applied to the analysis of extracellular and outer membrane proteins of A. pleuropneumoniae JL03 serotype 3 for the identification of novel immunogenic proteins for A. pleuropneumoniae.

Results

A total of 30 immunogenic proteins were identified from outer membrane and extracellular proteins of JL03 serotype 3, of which 6 were known antigens and 24 were novel immunogenic proteins for A. pleuropneumoniae.

Conclusion

These data provide information about novel immunogenic proteins for A. pleuropneumoniae serotype 3, and are expected to aid in development of novel vaccines against A. pleuropneumoniae.

Identification of Actinobacillus pleuropneumoniae genes important for survival during infection in its natural host

Actinobacillus pleuropneumoniae is a strict respiratory tract pathogen of swine and is the causative agent of porcine pleuropneumonia. We have used signature-tagged mutagenesis (STM) to identify genes required for survival of the organism within the pig. A total of 2,064 signature-tagged Tn10 transposon mutants were assembled into pools of 48 each, and used to inoculate pigs by the endotracheal route. Out of 105 mutants that were consistently attenuated in vivo, only 11 mutants showed a >2-fold reduction in growth in vitro compared to the wild type, whereas 8 of 14 mutants tested showed significant levels of attenuation in pig as evidenced from competitive index experiments. Inverse PCR was used to generate DNA sequence of the chromosomal domains flanking each transposon insertion. Only one sibling pair of mutants was identified, but three apparent transposon insertion hot spots were found--an anticipated consequence of the use of a Tn10-based system. Transposon insertions were found within 55 different loci, and similarity (BLAST) searching identified possible analogues or homologues for all but four of these. Matches included proteins putatively involved in metabolism and transport of various nutrients or unknown substances, in stress responses, in gene regulation, and in the production of cell surface components. Ten of the sequences have homology with genes involved in lipopolysaccharide and capsule production. The results highlight the importance of genes involved in energy metabolism, nutrient uptake and stress responses for the survival of A. pleuropneumoniae in its natural host: the pig.

Molecular cloning and analysis of a region of the Bartonella bacilliformis genome encoding NlpD, L-isoaspartyl methyltransferase and YajC homologs

The NlpD/LppB homolog of the human pathogen, Bartonella bacilliformis, is an immunogenic 43-kDa protein that is encoded by a 1206-bp open reading frame (ORF-401). The regions flanking the nlpD/lppB gene of B. bacilliformis were sequenced to determine if it is located within the rpoS operon, as it is in most bacteria. We report that the B. bacilliformis nlpD/lppB gene is located immediately downstream of pcm, a gene encoding a 25-kDa protein, L-isoaspartyl protein carboxyl methyltransferase, that is a component of the rpoS operon in other bacteria. However, the genomic organization downstream of the B. bacilliformis nlpD/lppB gene appears to be distinct. In other bacteria, the third gene in the operon is rpoS, a gene that codes for an alternative sigma factor of RNA polymerase. In B. bacilliformis, an open reading frame encoding a protein homologous to the immunodominant YajC protein is located directly downstream of the nlpD/lppB gene. We show that Bartonella henselae, a close relative of B. bacilliformis, also shares this unusual organizational feature. Thus, the genomic organization of the nlpD/lppB genes of B. bacilliformis, and B. henselae appears to be unique among all bacteria for which the sequence of this region has been reported.

Haemophilus somnus induces apoptosis in bovine endothelial cells in vitro

Haemophilus somnus causes pneumonia, reproductive failure, infectious myocarditis, thrombotic meningoencephalitis, and other diseases in cattle. Although vasculitis is commonly seen as a result of systemic H. somnus infections, the pathogenesis of vascular damage is poorly characterized. In this study, we demonstrated that H. somnus (pathogenic isolates 649, 2336, and 8025 and asymptomatic carrier isolates 127P and 129Pt) induce apoptosis of bovine endothelial cells in a time- and dose-dependent manner, as determined by Hoechst 33342 staining, terminal deoxynucleotidyl transferase-mediated dUTP-FITC nick end labeling, DNA fragmentation, and transmission electron microscopy. H. somnus induced endothelial cell apoptosis in as little as 1 h of incubation and did not require extracellular growth of the bacteria. Viable H. somnus organisms induced greater endothelial cell apoptosis than heat-killed organisms. Since viable H. somnus cells release membrane fibrils and blebs, which contain lipooligosaccharide (LOS) and immunoglobulin binding proteins, we examined culture filtrates for their ability to induce endothelial cell apoptosis. Culture filtrates induced similar levels of endothelial cell apoptosis, as did viable H. somnus organisms. Heat inactivation of H. somnus culture filtrates partially reduced the apoptotic effect on endothelial cells, which suggested the presence of both heat-labile and heat-stable factors. We found that H. somnus LOS, which is heat stable, induced endothelial cell apoptosis in a time- and dose-dependent manner and was inhibited by the addition of polymyxin B. These data demonstrate that H. somnus and its LOS induce endothelial cell apoptosis, which may play a role in producing vasculitis in vivo.

Molecular cloning, sequencing, expression, and characterization of an immunogenic 43-kilodalton lipoprotein of Bartonella bacilliformis that has homology to NlpD/LppB

A recombinant clone expressing an immunoreactive antigen of Bartonella bacilliformis was isolated by screening a genomic DNA library with serum from a patient with the chronic verruga phase of bartonellosis. The clone, pBIPIM-17, contained a partial open reading frame that expressed an immunoreactive fusion protein. Subsequent rescreening of the library by plaque hybridization resulted in the isolation of recombinant clones that contain the entire open reading frame. The open reading frame (ORF-401) is capable of encoding a protein of 401 amino acids with a predicted molecular mass of 43 kDa. The deduced amino acid sequence of the encoded protein was found to be highly homologous to a recently identified bacterial lipoprotein (LppB/NlpD) which has been associated with virulence. Evidence has been provided to show that the 43-kDa antigen of B. bacilliformis is a lipoprotein and that it is likely to use the same biosynthetic pathway as other bacterial lipoproteins. This is the first report to date that characterizes a lipoprotein of B. bacilliformis. The immunogenicity of the B. bacilliformis LppB homologue was demonstrated by Western blot analysis using sera from patients with clinical bartonellosis. Sera from patients who had a high titer for Bartonella henselae, the causative agent of bacillary angiomatosis and cat scratch disease, also recognized the recombinant 43-kDa antigen, suggesting that a homologue of this antigen is present in B. henselae. Using a cocktail of synthetic peptides corresponding to predicted major antigenic sites, polyclonal antiserum specific for the LppB homologue of B. bacilliformis was generated. This antiserum did not recognize the NlpD homologue of Escherichia coli or the 43-kDa antigen of B. henselae.

Cloning, sequencing, and phenotypic characterization of the rpoS gene from Pseudomonas putida KT2440

A gene homologous to the rpoS gene of Escherichia coli was cloned from a Pseudomonas putida KT2440 gene bank by complementation of the rpoS-deficient strain E. coli ZK918. The rpoS gene of P. putida complemented the acid sensitivity and catalase deficiency of the rpoS mutant of E. coli and stimulated expression of the RpoS-controlled promoter, bolAp1. The gene was sequenced and found to be highly similar to the rpoS genes of other gram-negative bacteria. Like in other gram-negative bacteria, a homolog of the nlpD gene was found upstream to the rpoS gene. A transcriptional fusion of the promoter of the P. putida rpoS gene to the luxAB genes from Vibrio harveyi was constructed and used as an inactivated allele of rpoS for gene replacement of the wild-type copy in the chromosome of P. putida. The resultant rpoS mutant of P.putida, C1R1, showed reduced survival of carbon starvation and reduced cross-protection against other types of stress in cells starved for carbon, in particular after a challenge with ethanol. Survival in soil amended with m-methylbenzoate was also reduced in the mutant strain P. putida C1R1. The RpoS protein of P. putida controls the expression of more than 50 peptides, which are normally expressed in cells after a short period of carbon starvation.

Growth-phase-dependent transcriptional regulation of the pcm and surE genes required for stationary-phase survival of Escherichia coli

Two neighbouring genes, surE and pcm, at 59 min on the Escherichia coli chromosome are both required for stationary-phase survival. Operon fusions of the putative promoter regions in front of surE (P2) or pcm (P3) with the lacZ reporter gene were constructed to study the transcriptional regulation of pcm and surE. Both promoter regions were able to activate beta-galactosidase activity in a growth-phase-dependent way in either rich or minimal medium. Induction from both promoters reached the highest level in late stationary phase and was independent of the rpoS/katF gene. Spent medium from early as well as late stationary-phase cultures could induce the expression of either promoter even after dialysis or boiling. A high cell density could induce the promoters more rapidly but not to a greater extent. It is proposed that the induction might be correlated with the decline in growth rate of the cells. The induction patterns of either P2 or P3 were very similar. pcm can thus be transcribed from both the P2 and P3 promoters that are regulated in similar ways.

Cloning and characterization of bacteriophage-like DNA from Haemophilus somnus homologous to phages P2 and HP1

In an attempt to identify and characterize components of a heme uptake system of Haemophilus somnus, an Escherichia coli cosmid library of H. somnus genomic DNA was screened for the ability to bind hemin (Hmb+). The Hmb+ phenotype was associated with a 7,814-bp HindIII fragment of H. somnus DNA that was subcloned and sequenced. Thirteen open reading frames (orfs) were identified, all transcribed in one direction, and transposon mutagenesis identified orf7 as the gene associated with the Hmb+ phenotype. Orf7 (178 amino acids) has extensive homology with the lysozymes of bacteriophages P-A2, P21, P22, PZA, phi-29, phi-vML3, T4, or HP1. The orf7 gene complemented the lytic function of the K gene of phage P2 and the R gene of phage lambda. A lysozyme assay using supernatants from whole-cell lysates of E. coli cultures harboring plasmid pRAP501 or pGCH2 (both of which express the orf7 gene product) exhibited significant levels of lysozyme activity. The orf6 gene upstream of orf7 has the dual start motif common to the holins encoded by lambdoid S genes, and the orf6 gene product has significant homology to the holins of phages HP1 and P21. When expressed from a tac promoter, the orf6 gene product caused immediate cell death without lysis, while cultures expressing the orf7 gene product grew at normal rates but lysed immediately after the addition of chloroform. Based on this data, we concluded that the Hmb+ phenotype was an artifact resulting from the expression of cloned lysis genes which were detrimental to the E. coli host. The DNA flanking the cloned lysis genes contains orfs that are similar to structural and DNA packaging genes of phage P2. Polyclonal antiserum against Orf2, which is homologous to the major capsid precursor protein (gpN) of phage P2, detected a 40,000-M(r) protein expressed from pRAP401 but did not detect Orf2 in H. somnus, lysates. The phage-like DNA was detected in the serum-susceptible preputial strains HS-124P and HS-127P but was absent from the serum-resistant preputial strains HS-20P and HS-22P. Elucidation of a potential role for this cryptic prophage in the H. somnus life cycle requires more study.

Purification and molecular characterization of glycylglycine endopeptidase produced by Staphylococcus capitis EPK1

A novel staphylolytic enzyme, ALE-1, acting on Staphylococcus aureus, was purified from a Staphylococcus capitis EPK1 culture supernatant. The optimal pH range for staphylolytic activity was 7 to 9. ALE-1 contains one Zn2+ atom per molecule. Analysis of peptidoglycan fragments released by ALE-1 indicated that the enzyme is a glycylglycine endopeptidase. The effects of various modulators were determined, and we found that o-phenanthroline, iodoacetic acid, diethylpyrocarbonate, and Cu2+ reduced the staphylolytic activity of ALE-1. beta-Casein, elastin, and pentaglycine were poor substrates for ALE-1. Molecular cloning data revealed that ALE-1 is composed of 362 amino acid residues and is synthesized as a precursor protein which is cleaved after Ala at position 35, thus producing a mature ALE-1 of 35.6 kDa. The primary structure of mature ALE-1 is very similar to the proenzyme form of lysostaphin. It has the modular design of an N-terminal domain of tandem repeats of a 13-amino-acid sequence fused to the active site containing C-terminal domain. Unlike lysostaphin, ALE-1 does not undergo processing of the N-terminal repeat domain in broth culture. ale-1 is encoded on the plasmid. Protein homology search suggested that ALE-1 and lysostaphin are members of the novel Zn2+ protease family with a homologous 38-amino-acid-long motif, Tyr-X-His-X(11)-Val-X(12/20)-Gly-X(5-6)-His.

Molecular cloning and characterization of nlpH, encoding a novel, surface-exposed, polymorphic, plasmid-encoded 33-kilodalton lipoprotein of Borrelia afzelii

Borrelia burgdorferi sensu lato organisms, comprising B. burgdorferi sensu stricto, Borrelia afzelii, and Borrelia garinii, are tick-borne pathogens causing Lyme borreliosis in humans. To identify putative virulence determinants, a B. afzelii DNA library was screened for Congo red dye binding, a property associated with virulence in pathogenic bacteria. One clone was found to carry a 663-nucleotide-long open reading frame encoding a Congo red dye-binding protein with a calculated molecular mass of 25,660 Da. The amino acid sequence deduced from its nucleotide sequence was found to include a consensus bacterial lipidation site present at residues 15 to 18 (Leu-Ser-Gly-Cys). The lipoprotein nature was demonstrated by incorporation of radioactive palmitate; hence, this protein has been termed NlpH, for new lipoprotein H. NlpH is located on the surface of B. afzelii, and the nlpH gene is found on a circular plasmid. The nlpH gene is also found in B. burgdorferi sensu stricto and B. garinii. Immediately upstream of nlpH is located a smaller reading frame encoding a polypeptide containing the casein kinase II phosphorylation recognition sequence, (Ser/Thr)-X-Y-(Glu/Asp), repeated 10 times.

A new gene involved in stationary-phase survival located at 59 minutes on the Escherichia coli chromosome

We determined the DNA sequence of a 2,232-bp region immediately upstream of the pcm gene at 59 min on the Escherichia coli chromosome that encodes an L-isoaspartyl protein methyltransferase with an important role in stationary-phase survival. Two open reading frames of 477 and 1,524 bp were found oriented in the same direction as that of the pcm gene. The latter open reading frame overlapped the 5' end of the pcm gene by 4 bp. Coupled in vitro transcription-translation analysis of DNA containing the 1,524-bp open reading frame directly demonstrated the production of a 37,000-Da polypeptide corresponding to a RNA species generated from a promoter within the open reading frame. The deduced amino acid sequence showed no similarity to known protein sequences. To test the function of this gene product, we constructed a mutant strain in which a kanamycin resistance element was inserted at a BstEII site in the middle of its coding region in an orientation that does not result in reduction of Pcm methyltransferase activity. These cells were found to survive poorly in stationary phase, at elevated temperatures, and in high-salt media compared with parent cells containing the intact gene, and we thus designate this gene surE (survival). surE appears to be the first gene of a bicistronic operon also containing the pcm gene. The phenotypes of mutations in either gene are very similar and indicate that both gene products are important for the viability of E. coli cells under stressful conditions.

The nlpD gene is located in an operon with rpoS on the Escherichia coli chromosome and encodes a novel lipoprotein with a potential function in cell wall formation

rpoS is the structural gene for sigma s, which is a second vegetative sigma subunit of RNA polymerase in Escherichia coli and is involved in the expression of many stationary phase-induced genes. Upstream of rpoS is an open reading frame (ORF) whose function and regulation have not been studied. Strong overproduction of its gene product using the IPTG-inducible tac promoter leads to the formation of bulges at the cell septum and the cell poles, and in rapidly growing cells brings about cell lysis, indicating that the gene product has a hydrolytic function in cell wall formation or maintenance. This is corroborated by sequence homology to lysostaphin, a cell wall lytic exoenzyme synthesized by two Staphylococcus strains. Using globomycin, a specific inhibitor of signal peptidase II, we demonstrate that the product of the ORF is a novel lipoprotein (NlpD). Two transcriptional start sites for nlpD have been localized. In contrast to rpoS, nlpD is not induced during entry into stationary phase. Growth-phase-regulated transcription of rpoS is initiated at additional sites within the nlpD ORF, but the nlpD promoters contribute substantially to the basal level of rpoS expression in exponentially growing cells, indicating that nlpD and rpoS form an operon.

A gene at 59 minutes on the Escherichia coli chromosome encodes a lipoprotein with unusual amino acid repeat sequences

We report a 1.432-kb DNA sequence at 59 min on the Escherichia coli chromosome that connects the published sequences of the pcm gene for the isoaspartyl protein methyltransferase and that of the katF or rpoS (katF/rpoS) gene for a sigma factor involved in stationary-phase gene expression. Analysis of the DNA sequence reveals an open reading frame potentially encoding a polypeptide of 379 amino acids. The polypeptide sequence includes a consensus bacterial lipidation sequence present at residues 23 to 26 (Leu-Ala-Gly-Cys), four octapeptide proline- and glutamine-rich repeats of consensus sequence QQPQIQPV, and four heptapeptide threonine- and serine-rich repeats of consensus sequence PTA(S,T)TTE. The deduced amino acid sequence, especially in the C-terminal region, is similar to that of the Haemophilus somnus LppB lipoprotein outer membrane antigen (40% overall sequence identity; 77% identity in last 95 residues). The LppB lipoprotein binds Congo red dye and has been proposed to be a virulence determinant in H. somnus. Utilizing a plasmid construct with the E. coli gene under the control of a phage T7 promoter, we demonstrate the lipidation of this gene product by the incorporation of [3H]palmitic acid into a 42-kDa polypeptide. We also show that treatment of E. coli cells with globomycin, an inhibitor of the lipoprotein signal peptidase, results in the accumulation of a 46-kDa precursor. We thus designate the protein NlpD (new lipoprotein D). E. coli cells overexpressing NlpD bind Congo red dye, suggesting a common function with the H. somnus LppB protein. Disruption of the chromosomal E. coli nlpD gene by insertional mutagenesis results in decreased stationary-phase survival after 7 days.