Identification and characterization of hemolysin-like proteins similar to RTX toxin in Pasteurella pneumotropica

Genomic and pathogenic characterization of RTX toxin producing Rodentibacter sp. that is closely related to Rodentibacter haemolyticus

Rodentibacter spp. are opportunistic pathogens that are often isolated from the upper respiratory tracts of laboratory rodents. In particular, R. pneumotropicus and R. heylii require considerable caution in rodent colonies, as they cause lethal pneumonia in rodents. A new species, R. haemolyticus, has recently been classified in the genus, and a very closely related strain, Rodentibacter sp. strain JRC, has been isolated in Japan. This study focused on strain JRC by performing genomic and pathogenic analyses. Draft genome sequencing of strain JRC identified several genes coding for putative virulent proteins, including hemolysin and adhesin. Furthermore, we found a new RTX (repeats-in-structural toxin) toxin gene in the genome, which was predicted to produce a critical virulence factor (RTXIA) similar to Enterobacteriaceae. The concentrated culture supernatant containing RTX toxin (RTXIA) showed cytotoxicity toward RAW264.7 cells. Pre-incubation with anti-CD11a attenuated the cytolysis, suggesting that the concentrated culture supernatant containing RTXIA is cell surface LFA-1 mediated cytolysin. Experimental infection of strain JRC intranasally with 5 female BALB/c-Rag2^-/- mice showed 60% lethality and was not significantly different from those of R. pneumotropicus ATCC 35149^T using the log-rank test. Combined with our finding that RTXIA has an almost identical amino acid sequence (98% identity) to that of R. haemolyticus 1625/19^T, these results strongly suggest that RTXIA-producing strain JRC (and related R. haemolyticus) is pathogenic to immunodeficient rodents, and both agents should be excluded in laboratory rodent colonies.

Identification of a large repetitive RTX immunogen in a highly virulent Rodentibacter heylii strain

Rodentibacter (R.) heylii is frequently detected in laboratory rodents. Repeats in toxin (RTX) toxins are considered important virulence factors of this major murine pathogen. We evaluated the virulence of a R.heylii strain negative for all known RTX toxin genes and Muribacter (M.) muris, a commensal in mice, in experimental infections of C57BL/6 and BALB/c mice. Experimental intranasal infection with 108 CFU of the pnxI-, pnxII- and pnxIII- R. heylii strain resulted in 75% and 100% mortality in C57BL/6 and BALB/c mice, respectively. In early losses, multiple internal organs were infected and purulent bronchopneumonia was the main pathology. Intranasal application of M. muris did not result in mortality or severe weight loss. Immunoproteomics led to the identification of a surface-associated and specific immunogen, which was designated as R. heylii immunogen A (RhiA) and which was exclusively recognised by sera obtained from mice infected with this R. heylii pathotype. RhiA is a 262.6 kDa large protein containing long imperfect tandem repeats and C-terminal RTX consensus sequences. Immunohistochemical analysis confirmed that this R.heylii pathotype expresses RhiA in the lower respiratory tract. In summary, this study describes a specific immunogen in a virulent R. heylii, strain which is an excellent antigen for pathotype-specific serological screenings and which might carry out RTX-related functions.

Comparative analysis of humoral immune responses and pathologies of BALB/c and C57BL/6 wildtype mice experimentally infected with a highly virulent Rodentibacter pneumotropicus (Pasteurella pneumotropica) strain

BACKGROUND

Mice are a natural host for Rodentibacter (R.) pneumotropicus. Despite specific monitoring, it is still one of the most important infectious agents in laboratory animals. The objective of this study was to determine the virulence of a prevalent pathotype of R. pneumotropicus and characterize the host response in a new animal model.

RESULTS

Intranasal infection of C57BL/6 and BALB/c mice with a R. pneumotropicus strain (JF4Ni) bearing the genes of the three known repeats in toxin (RTX) toxins resulted in an unprecedented high mortality and morbidity above 50 and 80%, respectively. Morbidity was associated with severe weight loss as well as conjunctivitis and dyspnea. A main pathology was a catarrhal purulent to necrotic bronchopneumonia. Specific immune globuline (Ig) A was detected in tracheonasal lavages of most surviving mice which were still colonized by R. pneumotropicus. Furthermore, all surviving animals showed a distinct production of IgG antibodies. To differentiate T-helper cell (Th) 1 and Th2 immune responses we used subclasses of IgGs as indicators. Mean ratios of IgG2b to IgG1 were below 0.8 in sera drawn from both mice strains prior infection and from BALB/c mice post infection. In contrast, C57BL/6 mice had a mean IgG2b/IgG1 ratio of 1.6 post infection indicating a Th1 immune response in C57BL/6 versus a Th2 response in BALB/c mice associated with a tenfold higher bacterial load in the lung. In accordance with a Th1 response high antigen-specific IgG2c titers were detected in the majority of surviving C57BL/6 mice.

CONCLUSIONS

R. pneumotropicus JF4Ni is a highly virulent strain causing severe pneumonia and septicemia after intranasal infection of C57BL/6 and BALB/c mice. Persisting infections in the two mice strains are associated with Th1 and Th2 immune responses, respectively, and differences in the bacterial burden of the lung. The described model is ideally suited for future vaccination studies using the natural host.

Clonal outbreaks of [ Pasteurella] pneumotropica biovar Heyl in two mouse colonies

The aim of this study was to document the pathogenic role of biovar Heyl of [ Pasteurella] pneumotropica in mouse colonies. Fifty-three isolates associated with mastitis and orbital, cutaneous and vaginal abscesses as well as isolates from the nose and vagina of healthy mice were investigated. According to phenotypic characteristics and rpoB sequencing, the isolates were identified as [ P.] pneumotropica biovar Heyl. Pulsed-field gel electrophoresis (PFGE) revealed five closely related profiles separated by only one to four fragments. The outbreak strains diverged from epidemiologically unrelated strains with the same rpoB sequence type, as shown by the PFGE profiles. The investigation documented that members of biovar Heyl of [ P.] pneumotropica caused disease outbreaks in mouse colonies since the clonality indicated a primary role of [ P.] pneumotropica biovar Heyl in the infections observed.

The Genomic Sequence of the Oral Pathobiont Strain NI1060 Reveals Unique Strategies for Bacterial Competition and Pathogenicity

Strain NI1060 is an oral bacterium responsible for periodontitis in a murine ligature-induced disease model. To better understand its pathogenicity, we have determined the complete sequence of its 2,553,982 bp genome. Although closely related to Pasteurella pneumotropica, a pneumonia-associated rodent commensal based on its 16S rRNA, the NI1060 genomic content suggests that they are different species thriving on different energy sources via alternative metabolic pathways. Genomic and phylogenetic analyses showed that strain NI1060 is distinct from the genera currently described in the family Pasteurellaceae, and is likely to represent a novel species. In addition, we found putative virulence genes involved in lipooligosaccharide synthesis, adhesins and bacteriotoxic proteins. These genes are potentially important for host adaption and for the induction of dysbiosis through bacterial competition and pathogenicity. Importantly, strain NI1060 strongly stimulates Nod1, an innate immune receptor, but is defective in two peptidoglycan recycling genes due to a frameshift mutation. The in-depth analysis of its genome thus provides critical insights for the development of NI1060 as a prime model system for infectious disease.

Identification of a virulence determinant that is conserved in the Jawetz and Heyl biotypes of [Pasteurella] pneumotropica

[Pasteurella] pneumotropica is a ubiquitous bacterium frequently isolated from laboratory rodents. Although this bacterium causes various diseases in immunosuppressed animals, little is known about major virulence factors and their roles in pathogenicity. To identify virulence factors, we sequenced the genome of [P.] pneumotropica biotype Heyl strain ATCC 12555, and compared the resulting non-contiguous draft genome sequence with the genome of biotype Jawetz strain ATCC 35149. Among a large number of genes encoding virulence-associated factors in both strains, four genes encoding for YadA-like proteins, which are known virulence factors that function in host cell adherence and invasion in many pathogens. In this study, we assessed YadA distribution and biological activity as an example of one of virulence-associated factor shared, with biotype Jawetz and Heyl. More than half of mouse isolates were found to have at least one of these genes; whereas, the majority of rat isolates did not. Autoagglutination activity, and ability to bind to mouse collagen type IV and mouse fibroblast cells, was significantly higher in YadA-positive than YadA-negative strains. To conclude, we identified a large number of candidate genes predicted to influence [P.] pneumotropica pathogenesis.

Characterization of Biofilm Formation in [Pasteurella] pneumotropica and [Actinobacillus] muris Isolates of Mouse Origin

[Pasteurella] pneumotropica biotypes Jawetz and Heyl and [Actinobacillus] muris are the most prevalent Pasteurellaceae species isolated from laboratory mouse. However, mechanisms contributing to their high prevalence such as the ability to form biofilms have not been studied yet. In the present investigation we analyze if these bacterial species can produce biofilms in vitro and investigate whether proteins, extracellular DNA and polysaccharides are involved in the biofilm formation and structure by inhibition and dispersal assays using proteinase K, DNase I and sodium periodate. Finally, the capacity of the biofilms to confer resistance to antibiotics is examined. We demonstrate that both [P.] pneumotropica biotypes but not [A.] muris are able to form robust biofilms in vitro, a phenotype which is widely spread among the field isolates. The biofilm inhibition and dispersal assays by proteinase and DNase lead to a strong inhibition in biofilm formation when added at the initiation of the biofilm formation and dispersed pre-formed [P.] pneumotropica biofilms, revealing thus that proteins and extracellular DNA are essential in biofilm formation and structure. Sodium periodate inhibited the bacterial growth when added at the beginning of the biofilm formation assay, making difficult the assessment of the role of β-1,6-linked polysaccharides in the biofilm formation, and had a biofilm stimulating effect when added on pre-established mature biofilms of [P.] pneumotropica biotype Heyl and a majority of [P.] pneumotropica biotype Jawetz strains, suggesting that the presence of β-1,6-linked polysaccharides on the bacterial surface might attenuate the biofilm production. Conversely, no effect or a decrease in the biofilm quantity was observed by biofilm dispersal using sodium periodate on further biotype Jawetz isolates, suggesting that polysaccharides might be incorporated in the biofilm structure. We additionally show that [P.] pneumotropica cells enclosed in biofilms were less sensitive to treatment with amoxicillin and enrofloxacin than planktonic bacteria. Taken together, these findings provide a first step in understanding of the biofilm mechanisms in [P.] pneumotropica, which might contribute to elucidation of colonization and pathogenesis mechanisms for these obligate inhabitants of the mouse mucosa.

Draft Genome Sequence of the Rodent Opportunistic Pathogen Pasteurella pneumotropica ATCC 35149T

Pasteurella pneumotropica is an opportunistic pathogen in rodents that is commonly isolated from upper respiratory tracts in laboratory rodents. Here, we report the draft genome sequence of the P. pneumotropica type strain ATCC 35149, which was first isolated and characterized as biotype Jawetz.

Pathogenicity of Pasteurella pneumotropica in immunodeficient NOD/ShiJic-scid/Jcl and immunocompetent Crlj:CD1 (ICR) mice

Pasteurella pneumotropica is an opportunistic pathogen in rodents. Natural infection in immunodeficient animals suggests that immunodeficiency is a major factor in P. pneumotropica pathogenesis. To understand this process, we performed clinical, pathological and bacteriological studies of immunodeficient NOD/ShiJic-scid/Jcl and immunocompetent Crlj:CD1 (ICR) mice experimentally infected with P. pneumotropica ATCC 35149. From 14 days postinoculation, some of P. pneumotropica-infected NOD/ShiJic-scid/Jcl mice developed clinical signs of weight loss. Three of 10 P. pneumotropica-infected NOD/ShiJic-scid/Jcl mice developed clinical signs of depression, ruffled coat, and weight loss and died at 27, 34, and 59 days postinoculation. At 35 days postinoculation, almost all P. pneumotropica-infected NOD/ShiJic-scid/Jcl mice had lung abscesses. The bacteria were isolated from the upper and lower respiratory tracts, including the lungs, and blood. In contrast, P. pneumotropica-infected ICR mice exhibited no clinical signs or lesions. The bacteria were isolated from the upper, but not the lower respiratory tracts. We developed an animal model for understanding host interactions with P. pneumotropica.

Ehrlichia chaffeensis tandem repeat proteins and Ank200 are type 1 secretion system substrates related to the repeats-in-toxin exoprotein family

Ehrlichia chaffeensis has type 1 and 4 secretion systems (T1SS and T4SS), but the substrates have not been identified. Potential substrates include secreted tandem repeat protein (TRP) 47, TRP120, and TRP32, and the ankyrin repeat protein, Ank200, that are involved in molecular host–pathogen interactions including DNA binding and a network of protein–protein interactions with host targets associated with signaling, transcriptional regulation, vesicle trafficking, and apoptosis. In this study we report that E. chaffeensis TRP47, TRP32, TRP120, and Ank200 were not secreted in the Agrobacterium tumefaciens Cre recombinase reporter assay routinely used to identify T4SS substrates. In contrast, all TRPs and the Ank200 proteins were secreted by the Escherichia coli complemented with the hemolysin secretion system (T1SS), and secretion was reduced in a T1SS mutant (ΔTolC), demonstrating that these proteins are T1SS substrates. Moreover, T1SS secretion signals were identified in the C-terminal domains of the TRPs and Ank200, and a detailed bioinformatic analysis of E. chaffeensis TRPs and Ank200 revealed features consistent with those described in the repeats-in-toxins (RTX) family of exoproteins, including glycine- and aspartate-rich tandem repeats, homology with ATP-transporters, a non-cleavable C-terminal T1SS signal, acidic pIs, and functions consistent with other T1SS substrates. Using a heterologous E. coli T1SS, this investigation has identified the first Ehrlichia T1SS substrates supporting the conclusion that the T1SS and corresponding substrates are involved in molecular host–pathogen interactions that contribute to Ehrlichia pathobiology. Further investigation of the relationship between Ehrlichia TRPs, Ank200, and the RTX exoprotein family may lead to a greater understanding of the importance of T1SS substrates and specific functions of T1SS in the pathobiology of obligately intracellular bacteria.

Molecular and virulence characteristics of an outer membrane-associated RTX exoprotein in Pasteurella pneumotropica

Background

Pasteurella pneumotropica is a ubiquitous bacterium that is frequently isolated from laboratory rodents and causes various clinical symptoms in immunodeficient animals. Currently two RTX toxins, PnxIA and PnxIIA, which are similar to hemolysin-like high-molecular-weight exoproteins are known in this species. In this study, we identified and analyzed a further RTX toxin named PnxIIIA and the corresponding type I secretion system.

Results

The RTX exoprotein, PnxIIIA, contains only a few copies of the RTX repeat-like sequence and 3 large repeat sequences that are partially similar to the outer membrane protein found in several prokaryotes. Recombinant PnxIIIA protein (rPnxIIIA) was cytotoxic toward J774A.1 mouse macrophage cells, whereas cytotoxicity was attenuated by the addition of anti-CD11a monoclonal antibody. rPnxIIIA could bind to extracellular matrices (ECMs) and cause hemagglutination of sheep erythrocytes. Binding was dependent on the 3 large repeat sequences in PnxIIIA. Protein interaction analyses indicated that PnxIIIA is mainly localized in the outer membrane of P. pneumotropica ATCC 35149 in a self-assembled oligomeric form. PnxIIIA is less cytotoxic to J774A.1 cells than PnxIA and PnxIIA.

Conclusions

The results implicate that PnxIIIA is located on the cell surface and participates in adhesion to ECMs and enhanced hemagglutination in the rodent pathogen P. pneumotropica.

In-depth analysis of exoproteomes from marine bacteria by shotgun liquid chromatography-tandem mass spectrometry: the Ruegeria pomeroyi DSS-3 case-study

Microorganisms secrete into their extracellular environment numerous compounds that are required for their survival. Many of these compounds could be of great interest for biotechnology applications and their genes used in synthetic biology design. The secreted proteins and the components of the translocation systems themselves can be scrutinized in-depth by the most recent proteomic tools. While the secretomes of pathogens are well-documented, those of non-pathogens remain largely to be established. Here, we present the analysis of the exoproteome from the marine bacterium Ruegeria pomeroyi DSS-3 grown in standard laboratory conditions. We used a shotgun approach consisting of trypsin digestion of the exoproteome, and identification of the resulting peptides by liquid chromatography coupled to tandem mass spectrometry. Three different proteins that have domains homologous to those observed in RTX toxins were uncovered and were semi-quantified as the most abundantly secreted proteins. One of these proteins clearly stands out from the catalogue, representing over half of the total exoproteome. We also listed many soluble proteins related to ABC and TRAP transporters implied in the uptake of nutrients. The Ruegeria pomeroyi DSS-3 case-study illustrates the power of the shotgun nano-LC-MS/MS strategy to decipher the exoproteome from marine bacteria and to contribute to environmental proteomics.