The virulence plasmid of Yersinia, an antihost genome

Yersinia enterocolitica Isolates from Wild Boars Hunted in Lower Saxony, Germany

Yersiniosis is strongly associated with the consumption of pork contaminated with enteropathogenic Yersinia enterocolitica, which is harbored by domestic pigs without showing clinical signs of disease. In contrast to data on Y. enterocolitica isolated from conventionally reared swine, investigations into the occurrence of Y. enterocolitica in wild boars in Germany are rare. The objectives of the study were to get knowledge about these bacteria and their occurrence in wild boars hunted in northern Germany by isolation of the bacteria from the tonsils, identification of the bioserotypes, determination of selected virulence factors, macrorestriction analysis, multilocus sequence typing (MLST), and testing of antimicrobial susceptibility. Altogether, tonsils from 17.1% of 111 tested wild boars were positive for Y. enterocolitica by culture methods. All but two isolates belonged to biotype (BT) 1A, with the majority of isolates bearing a ystB nucleotide sequence which was revealed to have 85% identity to internal regions of Y. enterocolitica heat-stable enterotoxin type B genes. The remaining Y. enterocolitica isolates were identified to be BT 1B and did not carry the virulence plasmid. However, two BT 1A isolates carried the ail gene. Macrorestriction analysis and results from MLST showed a high degree of genetic diversity of the isolates, although the region where the samples were taken was restricted to Lower Saxony, Germany, and wild boars were shot during one hunting season. In conclusion, most Y. enterocolitica isolates from wild boars investigated in this study belonged to biotype 1A. Enteropathogenic Y. enterocolitica bioserotypes 4/O:3 and 2/O:9, usually harbored by commercially raised pigs in Europe, could not be identified.

Proteomic analysis of Yersinia enterocolitica biovar 1A under iron-rich and iron-poor conditions indicate existence of efficiently regulated mechanisms of iron homeostasis

The pathogenicity of Yersinia enterocolitica biovar 1A strains is controversial as these lack most of the known virulence factors. Acquisition of iron and presence of well-regulated iron homeostasis in bacteria represents an important virulence trait. Differential abundance of proteins was examined under iron-rich and iron-poor conditions in a clinical Y. enterocolitica biovar 1A strain IP27407. Whole cell protein profiles were analysed by 2D gel electrophoresis (2D-GE). Following statistical and MALDI-TOF MS analyses, 28 differentially abundant proteins were identified. Significant iron-responsive changes were observed in the proteins involved in iron acquisition or storage namely, hemin receptor (HemR), periplasmic Fe(2+) transport protein (Tpd), periplasmic chelated iron-binding protein (YfeA) and bacterioferritin (Bfr). Quantitative real-time PCR (qRT-PCR) of eight mRNA transcripts revalidated the differential protein abundance. In silico analysis of iron homeostasis mediated by the bacterioferritin and bacterioferritin-associated ferredoxin (Bfr-Bfd) complex suggested two pathways for the release of reserve iron which might be operating under conditions of different iron availability. The study, for the first time, showed the existence of highly competent iron homeostasis mechanisms in Y. enterocolitica biovar 1A and identified the key proteins involved thereof. Such mechanisms might have implications for the pathogenicity of Y. enterocolitica biovar 1A strains.

BIOLOGICAL SIGNIFICANCE

Although, a few studies have identified the differentially abundant bacterial proteins in response to iron starvation, little information is available in this regard for Y. enterocolitica (especially, the biovar 1A strains). In the present study, differential abundance of several proteins was identified under iron-rich and iron-poor conditions by 2D-GE and MALDI-TOF/MS analysis. These included proteins which may not only be directly implicated in iron acquisition or storage but also play crucial role in cellular metabolism. Given the absence of most known virulence factors in Y. enterocolitica biovar 1A strains, demonstration of well-regulated mechanisms for efficient iron homeostasis constitutes an important observation. The proteins, as identified in the present study, provide useful insights to further unravel the potential pathogenicity of the biovar 1A strains.

Current activities of the Yersinia effector protein YopM

Yersinia outer protein M (YopM) belongs to the group of Yop effector proteins, which are highly conserved among pathogenic Yersinia species. During infection, the effectors are delivered into the host cell cytoplasm via the type 3 secretion system to subvert the host immune response and support the survival of Yersinia. In contrast to the other Yop effectors, YopM does not possess a known enzymatic activity and its molecular mechanism(s) of action remain(s) poorly understood. However, YopM was shown to promote colonization and dissemination of Yersinia, thus being crucial for the pathogen's virulence in vivo. Moreover, YopM interacts with several host cell proteins and might utilize them to execute its anti-inflammatory activities. The results obtained so far indicate that YopM is a multifunctional protein that counteracts the host immune defense by multiple activities, which are at least partially independent of each other. Finally, its functions seem to be also influenced by differences between the specific YopM isoforms expressed by Yersinia subspecies. In this review, we focus on the global as well as more specific contribution of YopM to virulence of Yersinia during infection and point out the various extra- and intracellular molecular functions of YopM. In addition, the novel cell-penetrating ability of recombinant YopM and its potential applications as a self-delivering immunomodulatory therapeutic will be discussed.

Proinflammatory microenvironments within the intestine regulate the differentiation of tissue-resident CD8⁺ T cells responding to infection

We report that oral infection with Yersinia pseudotuberculosis (Yptb) results in development of two distinct populations of pathogen-specific CD8 tissue-resident memory T (T_RM) cells in the lamina propria (LP). CD103^– T cells did not require transforming-growth factor-β (TGF-β) signaling, but were true resident memory cells. Unlike CD103⁺ CD8 T cells, which were TGF-β-dependent and scattered in the tissue, CD103^– T cells clustered with CD4 T cells and CX3CR1⁺ macrophages and/or dendritic cells around areas of bacterial infection. CXCR3-dependent recruitment to inflamed areas was critical for development of the CD103^– population and pathogen clearance. These studies have identified the preferential development of CD103^– LP T_RM cells in inflammatory microenvironments within the LP and suggest that this subset plays a critical role in controlling infection.

Chlamydia pneumoniae effector chlamydial outer protein N sequesters fructose bisphosphate aldolase A, providing a benefit to bacterial growth

Background

Pathogenic chlamydiae are obligate intracellular pathogens and have adapted successfully to human cells, causing sexually transmitted diseases or pneumonia. Chlamydial outer protein N (CopN) is likely a critical effector protein secreted by the type III secretion system in chlamydiae, which manipulates host cells. However, the mechanisms of its action remain to be clarified. In this work, we aimed to identify previously unidentified CopN effector target in host cells.

Results

We first performed a pull-down assay with recombinant glutathione S-transferase (GST) fusion CopN proteins (GST–CpCopN: Chlamydia pneumoniae TW183, GST–CtCopN: Chlamydia trachomatis D/UW-3/CX) as “bait” and soluble lysates obtained from human immortal epithelial HEp-2 cells as “prey”, followed by SDS-PAGE with mass spectroscopy (MS). We found that a host cell protein specifically bound to GST–CpCopN, but not GST–CtCopN. MS revealed the host protein to be fructose bisphosphate aldolase A (aldolase A), which plays a key role in glycolytic metabolism. We also confirmed the role of aldolase A in chlamydia-infected HEp-2 cells by using two distinct experiments for gene knockdown with an siRNA specific to aldolase A transcripts, and for assessment of glycolytic enzyme gene expression levels. As a result, both the numbers of chlamydial inclusion-forming units and RpoD transcripts were increased in the chlamydia-infected aldolase A knockdown cells, as compared with the wild-type HEp-2 cells. Meanwhile, chlamydial infection tended to enhance expression of aldolase A.

Conclusions

We discovered that one of the C. pneumoniae CopN targets is the glycolytic enzyme aldolase A. Sequestering aldolase A may be beneficial to bacterial growth in infected host cells.

Interrelationship between type three secretion system and metabolism in pathogenic bacteria

Before the advent of molecular biology methods, studies of pathogens were dominated by analyses of their metabolism. Development of molecular biology techniques then enabled the identification and functional characterisation of the fascinating toolbox of virulence factors. Increasing, genomic and proteomic approaches form the basis for a more systemic view on pathogens' functions in the context of infection. Re-emerging interest in the metabolism of pathogens and hosts further expands our view of infections. There is increasing evidence that virulence functions and metabolism of pathogens are extremely intertwined. Type three secretion systems (T3SSs) are major virulence determinants of many Gram-negative pathogens and it is the objective of this review to illustrate the intertwined relationship between T3SSs and the metabolism of the pathogens deploying them.

Transcriptomic response to Yersinia pestis: RIG-I like receptor signaling response is detrimental to the host against plague

Bacterial pathogens have evolved various mechanisms to modulate host immune responses for successful infection. In this study, RNA-sequencing technology was used to analyze the responses of human monocytes THP1 to Yersinia pestis infection. Over 6000 genes were differentially expressed over the 12 h infection. Kinetic responses of pathogen recognition receptor signaling pathways, apoptosis, antigen processing, and presentation pathway and coagulation system were analyzed in detail. Among them, RIG-I-like receptor (RLR) signaling pathway, which was established for antiviral defense, was significantly affected. Mice lacking MAVS, the adaptor of the RLR signaling pathway, were less sensitive to infection and exhibited lower IFN-β production, higher Th1-type cytokines IFN-γ and IL-12 production, and lower Th2-type cytokines IL-4 and IL-13 production in the serum compared with wild-type mice. Moreover, infection of pathogenic bacteria other than Y. pestis also altered the expression of the RLR pathway, suggesting that the response of RLR pathway to bacterial infection is a universal mechanism.

Two novel ail-positive biotype 1A strains of Yersinia enterocolitica isolated in China with unequal adhesion and invasion properties

Yersinia enterocolitica is an enteric pathogen having six biotypes: 1A, 1B, 2, 3, 4, and 5. Different bioserotypes have been associated with varying pathogenicity, and the strains of biotype 1A lack the virulence-associated pYV-bearing genes and were once considered to be avirulent. However, there is growing epidemiological, clinical, and experimental evidence to suggest some biotype 1A isolates are virulent and can cause gastrointestinal disease. Here, we describe two biotype 1A strains discovered from 3807 isolates that carry the ail (attachment and invasion locus) gene. The two strains showed unique PFGE patterns compared to all other isolates in the Chinese Y. enterocolitica isolate PFGE database. Strain SDWL-003 isolated from a sheep shared ail sequence identical to A1 pattern, and the foxA (ferrioxamine receptor) sequence was identical to the pathogenic F5 pattern, besides, the PFGE patterns of SDWL-003 was also cluster to pathogenic branch; however it does not attach to or invade Hep-2 cells. The ail sequence of strain 2006RAT isolated from a Microtus fortis showed several mutations compared to other published genomes, and therefore formed an entirely new pathogenic pattern. Though it clustered to non-pathogenic block with foxA sequence polymorphism analysis or PFGE assay, the strain 2006RAT showed adhesion properties. The data here bring new insights into the molecular genetics of Y. enterocolitica biotype 1A, show some isolates of 1A biotype gaining potential pathogenicity using the function of the virulence gene - ail, and indicate the lateral gene transfer of ail virulence genes proceeded between pathogenic and nonpathogenic Y. enterocolitica.

IscR is essential for yersinia pseudotuberculosis type III secretion and virulence

Type III secretion systems (T3SS) are essential for virulence in dozens of pathogens, but are not required for growth outside the host. Therefore, the T3SS of many bacterial species are under tight regulatory control. To increase our understanding of the molecular mechanisms behind T3SS regulation, we performed a transposon screen to identify genes important for T3SS function in the food-borne pathogen Yersinia pseudotuberculosis. We identified two unique transposon insertions in YPTB2860, a gene that displays 79% identity with the E. coliiron-sulfur cluster regulator, IscR. A Y. pseudotuberculosis iscR in-frame deletion mutant (ΔiscR) was deficient in secretion of Ysc T3SS effector proteins and in targeting macrophages through the T3SS. To determine the mechanism behind IscR control of the Ysc T3SS, we carried out transcriptome and bioinformatic analysis to identify Y. pseudotuberculosis genes regulated by IscR. We discovered a putative IscR binding motif upstream of the Y. pseudotuberculosis yscW-lcrF operon. As LcrF controls transcription of a number of critical T3SS genes in Yersinia, we hypothesized that Yersinia IscR may control the Ysc T3SS through LcrF. Indeed, purified IscR bound to the identified yscW-lcrF promoter motif and mRNA levels of lcrF and 24 other T3SS genes were reduced in Y. pseudotuberculosis in the absence of IscR. Importantly, mice orally infected with the Y. pseudotuberculosis ΔiscR mutant displayed decreased bacterial burden in Peyer's patches, mesenteric lymph nodes, spleens, and livers, indicating an essential role for IscR in Y. pseudotuberculosis virulence. This study presents the first characterization of Yersinia IscR and provides evidence that IscR is critical for virulence and type III secretion through direct regulation of the T3SS master regulator, LcrF.

Bacterial pathogens use regulators that sense environmental cues to enhance their fitness. Here, we identify a transcriptional regulator in the human gut pathogen, Yersinia pseudotuberculosis, which controls a specialized secretion system essential for bacterial growth in mammalian tissues. This regulator was shown in other bacterial species to alter its activity in response to changes in iron concentration and oxidative stress, but has never been studied in Yersinia. Importantly, Y. pseudotuberculosis experiences large changes in iron bioavailability upon transit from the gut to deeper tissues and iron is a critical component in Yersinia virulence, as individuals with iron overload disorders have enhanced susceptibility to systemic Yersinia infections. Our work places this iron-modulated transcriptional regulator within the regulatory network that controls virulence gene expression in Y. pseudotuberculosis, identifying it as a potential new target for antimicrobial agents.

Seroprevalence of enteropathogenic Yersinia spp. in pig batches at slaughter

Enteropathogenic Yersinia spp. are one of the main causes of foodborne bacterial infections in Europe. Slaughter pigs are the main reservoir and carcasses are contaminated during a sub-optimal hygienically slaughtering-process. Serology is potentially an easy option to test for the Yersinia-status of the pig (batches) before slaughter. A study of the variation in activity values (OD%) of Yersinia spp. in pigs and pig batches when applying a serological test were therefore conducted. In this study, pieces of the diaphragm of 7047 pigs, originating from 100 farms, were collected and meat juice was gathered, where after an enzyme-linked immunosorbent assay (ELISA) Pigtype Yopscreen (Labor Diagnostik Leipzig, Qiagen, Leipzig, Germany) was performed. The results were defined positive if the activity values exceeded the proposed cut-off value of 30 OD%. Results at pig level displayed a bimodal-shaped distribution with modes at 0-10% (n=879) and 50-60% (n=667). The average OD% was 51% and 66% of the animals tested positive. The within-batch seroprevalence ranged from 0 to 100% and also showed a bimodal distribution with modes at 0% (n=7) and 85-90% (n=16). On 7 farms, no single seropositive animal was present and in 22 farms, the mean OD% was below 30%. Based on the results obtained at slaughter, 66% of the pigs had contact with enteropathogenic Yersinia spp. at farm level. The latter occurred in at least 93% of the farms indicating that most farms are harboring enteropathogenic Yersinia spp.

Neisseria adhesin A variation and revised nomenclature scheme

Neisseria adhesin A (NadA), involved in the adhesion and invasion of Neisseria meningitidis into host tissues, is one of the major components of Bexsero, a novel multicomponent vaccine licensed for protection against meningococcal serogroup B in Europe, Australia, and Canada. NadA has been identified in approximately 30% of clinical isolates and in a much lower proportion of carrier isolates. Three protein variants were originally identified in invasive meningococci and named NadA-1, NadA-2, and NadA-3, whereas most carrier isolates either lacked the gene or harbored a different variant, NadA-4. Further analysis of isolates belonging to the sequence type 213 (ST-213) clonal complex identified NadA-5, which was structurally similar to NadA-4, but more distantly related to NadA-1, -2, and -3. At the time of this writing, more than 89 distinct nadA allele sequences and 43 distinct peptides have been described. Here, we present a revised nomenclature system, taking into account the complete data set, which is compatible with previous classification schemes and is expandable. The main features of this new scheme include (i) the grouping of the previously named NadA-2 and NadA-3 variants into a single NadA-2/3 variant, (ii) the grouping of the previously assigned NadA-4 and NadA-5 variants into a single NadA-4/5 variant, (iii) the introduction of an additional variant (NadA-6), and (iv) the classification of the variants into two main groups, named groups I and II. To facilitate querying of the sequences and submission of new allele sequences, the nucleotide and amino acid sequences are available at http://pubmlst.org/neisseria/NadA/.

Radiation resistance and loss of crystal violet binding activity in Yersinia enterocolitica suspended in raw ground pork exposed to gamma radiation and modified atmosphere

Virulence of many foodborne pathogens is directly linked to genes carried on self-replicating extra-chromosomal elements, which can transfer genetic material, both vertically and horizontally, between bacteria of the same and different species. Pathogenic Yersinia enterocolitica harbors a 70-kb virulence plasmid (pYV) that encodes genes for low calcium response, crystal violet (CV) binding, Congo red uptake, autoagglutination (AA), hydrophobicity (HP), type III secretion channels, host immune suppression factors, and biofilm formation. Ionizing radiation and modified atmosphere packaging (MAP) are used to control foodborne pathogens and meat spoilage. In this study, the effect of gamma radiation and modified atmosphere (air, 100% N2 , 75% N2 : 25% CO2 , 50% N2 : 50% CO2 , 25% N2 : 75% CO2 , 100% CO2 ) were examined by using the CV binding phenotype, for the presence or absence of pYV in Y. enterocolitica, suspended in raw ground pork. All Y. enterocolitica serovars used (O:3, O:8, and O5,27) were more sensitive to radiation as the CO2 concentration increased above 50%. Crystal violet binding following a radiation dose of 1.0 kGy, which reduced the Y. enterocolitica serovars >5 log, was greatest in the presence of air (ca. 8%), but was not affected by N2 or CO2 concentration (ca. 5%). Following release from modified atmosphere after irradiation, the loss of CV binding rose from 5% to 8% immediately following irradiation to >30% after outgrowth at 25 °C for 24 h. These results, using Y. enterocolitica as a model system, indicate that the risk of foodborne illness could be affected by the loss of virulence factors when postprocess intervention technologies are used.

PRACTICAL APPLICATION

Provides gamma radiation D10 data for inactivation data for Y. enterocolitica irradiated under modified atmosphere and information to risk assessors regarding the difference between pathogen presence versus actual virulence.

Temperature-driven differential gene expression by RNA thermosensors

Many prokaryotic genes are organized in operons. Genes organized in such transcription units are co-transcribed into a polycistronic mRNA. Despite being clustered in a single mRNA, individual genes can be subjected to differential regulation, which is mainly achieved at the level of translation depending on initiation and elongation. Efficiency of translation initiation is primarily determined by the structural accessibility of the ribosome binding site (RBS). Structured cis-regulatory elements like RNA thermometers (RNATs) can contribute to differential regulation of individual genes within a polycistronic mRNA. RNATs are riboregulators that mediate temperature-responsive regulation of a downstream gene by modulating the accessibility of its RBS. At low temperature, the RBS is trapped by intra-molecular base pairing prohibiting translation initiation. The secondary structure melts with increasing temperature thus liberating the RBS. Here, we present an overview of different RNAT types and specifically highlight recently discovered RNATs. The main focus of this review is on RNAT-based differential control of polycistronic operons. Finally, we discuss the influence of temperature on other riboregulators and the potential of RNATs in synthetic RNA biology. This article is part of a Special Issue entitled: Riboswitches.

LcrQ blocks the role of LcrF in regulating the Ysc-Yop type III secretion genes in Yersinia pseudotuberculosis

Pathogenic Yersinia species employ the Ysc-Yop type III secretion system (T3SS) encoded by a highly conserved pYV virulence plasmid to export the virulence effectors into host cells. The Ysc-Yop T3SS is tightly regulated by multiple contributing proteins that function at different levels. However, systematic transcriptional regulation analysis of Ysc-Yop T3SS is lacking and the detailed mechanism under this regulation process is still elusive. Aimed at systematically characterizing transcriptional regulations of all T3SS genes in Y. pseudotuberculosis, we amplified 97 non-coding fragments from the pYV plasmid and analyzed transcriptional responses of the T3SS genes under different growth conditions. Transcriptions of T3SS genes were induced at 37°C and genes encoding T3SS effectors were highly induced by further depletion of Ca2+. The temperature induced gene transcription process is mediated by modules encoded on the chromosome, while the Ca2+ depletion-induced process is controlled by the positive regulatory protein LcrF as well as the negative regulatory protein LcrQ. In this process, LcrQ shares the same targets with LcrF and the effect of LcrQ is dependent on the presence of LcrF. Furthermore, over-expression of LcrF showed the same phenotype as that of the lcrQ mutant strain and intracellular amount balance of LcrQ and LcrF is important in T3SS regulation. When the expression level of LcrF exceeds LcrQ, expression of the Ysc-Yop T3SS genes is activated and vice versa. Together, these data support a model in which LcrQ blocks the activation role of LcrF in regulating the transcription of T3SS genes in Yersinia.

Gene polymorphism analysis of Yersinia enterocolitica outer membrane protein A and putative outer membrane protein A family protein

Background

Yersinia enterocolitica outer membrane protein A (OmpA) is one of the major outer membrane proteins with high immunogenicity. We performed the polymorphism analysis for the outer membrane protein A and putative outer membrane protein A (p-ompA) family protein gene of 318 Y. enterocolitica strains.

Results

The data showed all the pathogenic strains and biotype 1A strains harboring ystB gene carried both ompA and p-ompA genes; parts of the biotype 1A strains not harboring ystB gene carried either ompA or p-ompA gene. In non-pathogenic strains (biotype 1A), distribution of the two genes and ystB were highly correlated, showing genetic polymorphism. The pathogenic and non-pathogenic, highly and weakly pathogenic strains were divided into different groups based on sequence analysis of two genes. Although the variations of the sequences, the translated proteins and predicted secondary or tertiary structures of OmpA and P-OmpA were similar.

Conclusions

OmpA and p-ompA gene were highly conserved for pathogenic Y. enterocolitica. The distributions of two genes were correlated with ystB for biotype 1A strains. The polymorphism analysis results of the two genes probably due to different bio-serotypes of the strains, and reflected the dissemination of different bio-serotype clones of Y. enterocolitica.

Bacterial serine/threonine protein kinases in host-pathogen interactions

In bacterial pathogenesis, monitoring and adapting to the dynamically changing environment in the host and an ability to disrupt host immune responses are critical. The virulence determinants of pathogenic bacteria include the sensor/signaling proteins of the serine/threonine protein kinase (STPK) family that have a dual role of sensing the environment and subverting specific host defense processes. STPKs can sense a wide range of signals and coordinate multiple cellular processes to mount an appropriate response. Here, we review some of the well studied bacterial STPKs that are essential virulence factors and that modify global host responses during infection.

The Yersinia pseudotuberculosis complex: characterization and delineation of a new species, Yersinia wautersii

The genus Yersinia contains three species pathogenic for humans, one of which is the enteropathogen Yersinia pseudotuberculosis. A recent analysis by Multi Locus Sequence Typing (MLST) of the 'Y. pseudotuberculosis complex' revealed that this complex comprises three distinct populations: the Y. pestis/Y. pseudotuberculosis group, the recently described species Yersinia similis, and a third not yet characterized population designated 'Korean Group', because most strains were isolated in Korea. The aim of this study was to perform an in depth phenotypic and genetic characterization of the three populations composing the Y. pseudotuberculosis complex (excluding Y. pestis, which belonged to the Y. pseudotuberculosis cluster in the MLST analysis). Using a set of strains representative of each group, we found that the three populations had close metabolic properties, but were nonetheless distinguishable based on D-raffinose and D-melibiose fermentation, and on pyrazinamidase activity. Moreover, high-resolution electrospray mass spectrometry highlighted protein peaks characteristic of each population. Their 16S rRNA gene sequences shared high identity (≥99.5%), but specific nucleotide signatures for each group were identified. Multi-Locus Sequence Analysis also identified three genetically closely related but distinct populations. Finally, an Average Nucleotide Identity (ANI) analysis performed after sequencing the genomes of a subset of strains of each group also showed that intragroup identity (average for each group ≥99%) was higher than intergroup diversity (94.6-97.4%). Therefore, all phenotypic and genotypic traits studied concurred with the initial MLST data indicating that the Y. pseudotuberculosis complex comprises a third and clearly distinct population of strains forming a novel Yersinia species that we propose to designate Yersinia wautersii sp. nov. The isolation of some strains from humans, the detection of virulence genes (on the pYV and pVM82 plasmids, or encoding the superantigen ypmA) in some isolates, and the absence of pyrazinamidase activity (a hallmark of pathogenicity in the genus Yersinia) argue for the pathogenic potential of Y. wautersii.

Genome-wide analysis of small RNAs expressed by Yersinia pestis identifies a regulator of the Yop-Ysc type III secretion system

Small noncoding RNA (sRNA) molecules are integral components of the regulatory machinery for many bacterial species and are known to posttranscriptionally regulate metabolic and stress-response pathways, quorum sensing, virulence factors, and more. The Yop-Ysc type III secretion system (T3SS) is a critical virulence component for the pathogenic Yersinia species, and the regulation of this system is tightly controlled at each step from transcription to translocation of effectors into host cells. The contribution of sRNAs to the regulation of the T3SS in Yersinia has been largely unstudied, however. Previously, our lab identified a role for the sRNA chaperone protein Hfq in the regulation of components of the T3SS in the gastrointestinal pathogen Yersinia pseudotuberculosis. Here we present data demonstrating a similar requirement for Hfq in the closely related species Yersinia pestis. Through deep sequencing analysis of the Y. pestis sRNA-ome, we found 63 previously unidentified putative sRNAs in this species. We identified a Yersinia-specific sRNA, Ysr141, carried by the T3SS plasmid pCD1 that is required for the production of multiple T3SS proteins. In addition, we show that Ysr141 targets an untranslated region upstream of yopJ to posttranscriptionally activate the synthesis of the YopJ protein. Furthermore, Ysr141 may be an unstable and/or processed sRNA, which could contribute to its function in the regulation of the T3SS. The discovery of an sRNA that influences the synthesis of the T3SS adds an additional layer of regulation to this tightly controlled virulence determinant of Y. pestis.

In Silico Molecular Characterization of Cysteine Protease YopT from Yersinia pestis by Homology Modeling and Binding Site Identification

Plague is a major health concern and Yersinia pestis plays the central causal role in this disease. Yersinia pestis has developed resistance against the commonly available drugs. So, it is now a key concern to find a new drug target. Cysteine protease YopT enzyme is an important factor used by Yersinia pestis for pathogenesis in its host and it has the anti-phagocytic function of removal of C-termini lipid modification. The 3D structure of cysteine protease YopT of Yersinia pestis was determined by means of homology modeling through multiple alignments followed by intensive optimization and validation. The modeling was done by Phyre 2 and refined by ModRefiner. The obtained model was verified with structure validation programs such as PROCHECK, verify 3D and ERRAT for reliability. Interacting partners and active sites were also determined. PROCHECK analysis showed that 93% of the residues are in the most favored region, 5.9% are in the additional allowed region and 1.1% are in the generously allowed region of the Ramachandran plot. The verify 3D value of 0.78 indicates that the environmental profile of the model is good. SOPMA is employed for calculation of the secondary structural features of cysteine protease YopT. Active site determination through CASTp proposes that this protein can be utilized as a potential drug target. However, these findings should further be confirmed by wet lab studies for a targeted therapeutic agent design against Yersinia pestis.

Host–pathogen interactions: a proteomic view

Host-pathogen interactions reflect the balance of host defenses and pathogen virulence mechanisms. Advances in proteomic technologies now afford opportunities to compare protein content between complex biologic systems ranging from cells to animals and clinical samples. Thus, it is now possible to characterize host-pathogen interactions from a global proteomic view. Most reports to date focus on cataloging protein content of pathogens and identifying virulence-associated proteins or proteomic alterations in host response. A more in-depth understanding of host-pathogen interactions has the potential to improve our mechanistic understanding of pathogenicity and virulence, thereby defining novel therapeutic and vaccine targets. In addition, proteomic characterization of the host response can provide pathogen-specific host biomarkers for rapid pathogen detection and characterization, as well as for early and specific detection of infectious diseases. A review of host-pathogen interactions focusing on proteomic analyses of both pathogen and host will be presented. Relevant genomic studies and host model systems will be also be discussed.

YfbA, a Yersinia pestis regulator required for colonization and biofilm formation in the gut of cat fleas

For transmission to new hosts, Yersinia pestis, the causative agent of plague, replicates as biofilm in the foregut of fleas that feed on plague-infected animals or humans. Y. pestis biofilm formation has been studied in the rat flea; however, little is known about the cat flea, a species that may bridge zoonotic and anthroponotic plague cycles. Here, we show that Y. pestis infects and replicates as a biofilm in the foregut of cat fleas in a manner requiring hmsFR, two determinants for extracellular biofilm matrix. Examining a library of transposon insertion mutants, we identified the LysR-type transcriptional regulator YfbA, which is essential for Y. pestis colonization and biofilm formation in cat fleas.

Ail proteins of Yersinia pestis and Y. pseudotuberculosis have different cell binding and invasion activities

The Yersinia pestis adhesin Ail mediates host cell binding and facilitates delivery of cytotoxic Yop proteins. Ail from Y. pestis and Y. pseudotuberculosis is identical except for one or two amino acids at positions 43 and 126 depending on the Y. pseudotuberculosis strain. Ail from Y. pseudotuberculosis strain YPIII has been reported to lack host cell binding ability, thus we sought to determine which amino acid difference(s) are responsible for the difference in cell adhesion. Y. pseudotuberculosis YPIII Ail expressed in Escherichia coli bound host cells, albeit at ~50% the capacity of Y. pestis Ail. Y. pestis Ail single mutants, Ail-E43D and Ail-F126V, both have decreased adhesion and invasion in E. coli when compared to wild-type Y. pestis Ail. Y. pseudotuberculosis YPIII Ail also had decreased binding to the Ail substrate fibronectin, relative to Y. pestis Ail in E. coli. When expressed in Y. pestis, there was a 30-50% decrease in adhesion and invasion depending on the substitution. Ail-mediated Yop delivery by both Y. pestis Ail and Y. pseudotuberculosis Ail were similar when expressed in Y. pestis, with only Ail-F126V giving a statistically significant reduction in Yop delivery of 25%. In contrast to results in E. coli and Y. pestis, expression of Ail in Y. pseudotuberculosis led to no measurable adhesion or invasion, suggesting the longer LPS of Y. pseudotuberculosis interferes with Ail cell-binding activity. Thus, host context affects the binding activities of Ail and both Y. pestis and Y. pseudotuberculosis Ail can mediate cell binding, cell invasion and facilitate Yop delivery.

Yersinia Ysc-Yop type III secretion feedback inhibition is relieved through YscV-dependent recognition and secretion of LcrQ

Human pathogenic Yersinia species share a virulence plasmid encoding the Ysc-Yop type III secretion system (T3SS). A plasmid-encoded anti-activator, LcrQ, negatively regulates the expression of this secretion system. Under inducible conditions, LcrQ is secreted outside of bacterial cells and this activates the T3SS, but the mechanism of targeting LcrQ for type III secretion remains largely unknown. In this study, we characterized the regulatory role of the export apparatus component YscV. Depletion or overexpression of YscV compromised Yop synthesis and this primarily prevented secretion of LcrQ. It followed that a lcrQ deletion reversed the repressive effects of excessive YscV. Further characterization demonstrated that the YscV residues 493-511 located within the C-terminal soluble cytoplasmic domain directly bound with LcrQ. Critically, YscV-LcrQ complex formation was a requirement for LcrQ secretion, since YscVΔ493-511 failed to secrete LcrQ. This forced a cytoplasmic accumulation of LcrQ, which predictably caused the feedback inhibition of Yops synthesis. Based on these observations, we proposed a model for the YscV-dependent secretion of LcrQ and its role in regulating Yop synthesis in Yersinia.

Essential role of invasin for colonization and persistence of Yersinia enterocolitica in its natural reservoir host, the pig

In this study, an oral minipig infection model was established to investigate the pathogenicity of Yersinia enterocolitica bioserotype 4/O:3. O:3 strains are highly prevalent in pigs, which are usually symptomless carriers, and they represent the most common cause of human yersiniosis. To assess the pathogenic potential of the O:3 serotype, we compared the colonization properties of Y. enterocolitica O:3 with O:8, a highly mouse-virulent Y. enterocolitica serotype, in minipigs and mice. We found that O:3 is a significantly better colonizer of swine than is O:8. Coinfection studies with O:3 mutant strains demonstrated that small variations within the O:3 genome leading to higher amounts of the primary adhesion factor invasin (InvA) improved colonization and/or survival of this serotype in swine but had only a minor effect on the colonization of mice. We further demonstrated that a deletion of the invA gene abolished long-term colonization in the pigs. Our results indicate a primary role for invasin in naturally occurring Y. enterocolitica O:3 infections in pigs and reveal a higher adaptation of O:3 than O:8 strains to their natural pig reservoir host.

Production of Autoantibodies Associated with Polyclonal Activation inYersinia enterocoliticaO:8-Infected Mice

Polyclonal lymphocyte stimulation is one of the immunomodulatory mechanisms induced by arthritogenic pathogens. In this study we examined the polyclonal activation potential of a virulent strain of Y. enterocolitica serotype O: 8 (WA 2707(+)) and its plasmidless isogenic pair (WA 2707(-)). SPF Swiss mice were infected intragastrically and spleen cells were obtained on days 7, 14, 21, 28, 35 and 42 after infection. The number of cells secreting nonspecific immunoglobulins of IgG, IgM and IgA isotypes was determined by the ELISPOT technique. The presence of serum-specific antibodies was investigated by ELISA and the presence of autoantibodies by dot-blot assay. Although the patterns of infection of the two bacterial strains were almost the same, only the animals infected with the virulent strain presented clinical anomalies. Neither arthritic nor inflammatory signs were observed in the joints of the infected animals. The greatest activation observed was that of the nonspecific IgM-secreting cells, and their peak of secretion occurred between the 28th and the 42nd day after infection, for both strains of Y. enterocolitica O: 8. Only the animals infected with the virulent strain (WA 2707(+)) produced IgG-specific antibodies in the serum, from the 28th day after infection. The serum of animals infected with either strain showed reactivity to all the autologous constituents tested, mainly on the 28th and 42nd day after infection. It was concluded that infection of mice with either the virulent strain of Y. enterocolitica O: 8 or with its plasmidless isogenic pair resulted in the polyclonal activation of the splenic B lymphocytes including some autoreactive clones.

The cytotoxic necrotizing factor of Yersinia pseudotuberculosis (CNFY) enhances inflammation and Yop delivery during infection by activation of Rho GTPases

Some isolates of Yersinia pseudotuberculosis produce the cytotoxic necrotizing factor (CNF_Y), but the functional consequences of this toxin for host-pathogen interactions during the infection are unknown. In the present study we show that CNF_Y has a strong influence on virulence. We demonstrate that the CNF_Y toxin is thermo-regulated and highly expressed in all colonized lymphatic tissues and organs of orally infected mice. Most strikingly, we found that a cnfY knock-out variant of a naturally toxin-expressing Y. pseudotuberculosis isolate is strongly impaired in its ability to disseminate into the mesenteric lymph nodes, liver and spleen, and has fully lost its lethality. The CNF_Y toxin contributes significantly to the induction of acute inflammatory responses and to the formation of necrotic areas in infected tissues. The analysis of the host immune response demonstrated that presence of CNF_Y leads to a strong reduction of professional phagocytes and natural killer cells in particular in the spleen, whereas loss of the toxin allows efficient tissue infiltration of these immune cells and rapid killing of the pathogen. Addition of purified CNF_Y triggers formation of actin-rich membrane ruffles and filopodia, which correlates with the activation of the Rho GTPases, RhoA, Rac1 and Cdc42. The analysis of type III effector delivery into epithelial and immune cells in vitro and during the course of the infection further demonstrated that CNF_Y enhances the Yop translocation process and supports a role for the toxin in the suppression of the antibacterial host response. In summary, we highlight the importance of CNF_Y for pathogenicity by showing that this toxin modulates inflammatory responses, protects the bacteria from attacks of innate immune effectors and enhances the severity of a Yersinia infection.

Various toxins and effector proteins of bacterial pathogens have been found to manipulate eukaryotic cell machineries to promote persistence and proliferation within their hosts. Many of these virulence factors target small Rho GTPases, but their role in pathogenesis is often unknown. Here, we addressed the expression and functional consequences of the CNF_Y toxin found in some isolates of Y. pseudotuberculosis. We found that CNF_Y besides modulating the cell cytoskeleton by activation of the GTPases RhoA, Rac1 and Cdc42, contributes to increased inflammation and tissue damage. Moreover, CNF_Y increases the ability of Yersinia to prevent the attack of the immune system, by enhancing the delivery of antiphagocytic and cytotoxic effectors into professional phagocytes. Our findings provide the first insights into the multi-functional action and severe consequences of the CNF_Y toxin on the inflammatory response and disease-associated tissue damage during the natural course of the infection.

Translational regulation of Yersinia enterocolitica mRNA encoding a type III secretion substrate

Yersinia enterocolitica type III secretion machines transport YopQ and other Yop effectors into host immune cells. YopD and its chaperone LcrH are essential components of the Yersinia type III pathway, enabling effector translocation into host cells. YopD, LcrH, and YscM1 also regulate yop expression post-transcriptionally in response to environmental signals; however, the molecular mechanisms for this regulation and Yop secretion are unknown. We show here that YopD associates with 30 S ribosomal particles in a manner requiring LcrH. When added to ribosomes, YopD, LcrH, and YscM1 block the translation of yopQ mRNA. We propose a model whereby LcrH-dependent association of YopD with 30 S ribosomal particles enables YscM1 to block yopQ translation unless type III machines are induced to secrete the effector.

Comparison of cytokine immune responses to Brucella abortus and Yersinia enterocolitica serotype O:9 infections in BALB/c mice

Brucella abortus and Yersinia enterocolitica serotype O:9 serologically cross-react in the immune response with the host; therefore, our aim was to compare the immune responses to these two pathogens. We selected typical B. abortus and Y. enterocolitica O:9 strains to study the cytokine immune response and the histopathological changes in livers and spleens of BALB/c mice. The data showed the cytokine responses to the two strains of pathogens were different, where the average levels of granulocyte-macrophage colony-stimulating factor (GM-CSF), gamma interferon (IFN-γ), interleukin-12 (IL-12), and tumor necrosis factor alpha (TNF-α) were higher with B. abortus infections than with Y. enterocolitica O:9 infections, especially for IFN-γ, while the IL-10 level was lower and the levels of IL-1β, IL-4, IL-5, and IL-6 were similar. The histopathological effects in the livers and spleens of the BALB/c mice with B. abortus and Y. enterocolitica O:9 infections were similar; however, the pathological changes in the liver were greater with B. abortus infections, while damage in the spleen was greater with Y. enterocolitica O:9 infections. These observations show that different cytokine responses and histopathological changes occur with B. abortus and Y. enterocolitica O:9 infections.

Evaluation of YadC protein delivered by live attenuated Salmonella as a vaccine against plague

Yersinia pestis YadB and YadC are two new outer membrane proteins related to its pathogenicity. Here, codon-optimized yadC, yadC810 (aa 32-551), or yadBC antigen genes delivered by live attenuated Salmonella strains are evaluated in mice for induction of protective immune responses against Y. pestis CO92 through subcutaneous or intranasal challenge. Our findings indicate that mice immunized with Salmonella synthesizing YadC, YadC810, or YadBC develop significant serum IgG responses to purified recombinant YadC protein. For subcutaneous challenge (approximately 230 LD50 of Y. pestis CO92), mice immunized with Salmonella synthesizing YadC or YadC810 are afforded 50% protection, but no protection by immunization with the Salmonella strain synthesizing YadBC. None of these antigens provided protection against intranasal challenge (approximately 31 LD50 of Y. pestis CO92). In addition, subcutaneous immunization with purified YadC810 protein emulsified with alum adjuvant does not elicit a protective response against Y. pestis administered by either challenge route.

Human and animal isolates of Yersinia enterocolitica show significant serotype-specific colonization and host-specific immune defense properties

Yersinia enterocolitica is a human pathogen that is ubiquitous in livestock, especially pigs. The bacteria are able to colonize the intestinal tract of a variety of mammalian hosts, but the severity of induced gut-associated diseases (yersiniosis) differs significantly between hosts. To gain more information about the individual virulence determinants that contribute to colonization and induction of immune responses in different hosts, we analyzed and compared the interactions of different human- and animal-derived isolates of serotypes O:3, O:5,27, O:8, and O:9 with murine, porcine, and human intestinal cells and macrophages. The examined strains exhibited significant serotype-specific cell binding and entry characteristics, but adhesion and uptake into different host cells were not host specific and were independent of the source of the isolate. In contrast, survival and replication within macrophages and the induced proinflammatory response differed between murine, porcine, and human macrophages, suggesting a host-specific immune response. In fact, similar levels of the proinflammatory cytokine macrophage inflammatory protein 2 (MIP-2) were secreted by murine bone marrow-derived macrophages with all tested isolates, but the equivalent interleukin-8 (IL-8) response of porcine bone marrow-derived macrophages was strongly serotype specific and considerably lower in O:3 than in O:8 strains. In addition, all tested Y. enterocolitica strains caused a considerably higher level of secretion of the anti-inflammatory cytokine IL-10 by porcine than by murine macrophages. This could contribute to limiting the severity of the infection (in particular of serotype O:3 strains) in pigs, which are the primary reservoir of Y. enterocolitica strains pathogenic to humans.

Molecular analysis of a novel Toll/interleukin-1 receptor (TIR)-domain containing virulence protein of Y. pseudotuberculosis among Far East scarlet-like fever serotype I strains

Pathogenicity of Yersinia pseudotuberculosis is determined by an arsenal of virulence factors. Particularly, the Yersinia outer proteins (Yops) and the Type III secretion system (T3SS) encoded on the pYV virulence plasmid are required for Yersinia pathogenicity. A specific group of Y. pseudotuberculosis, responsible for the clinical syndrome described as Far East scarlet-like fever (FESLF), is known to have an altered virulence gene cluster. Far East strains cause unique clinical symptoms for which the pYV virulence plasmid plays apparently a rather secondary role. Here, we characterize a previously unknown protein of Y. pseudotuberculosis serotype I strains (TcpYI) which can be found particularly among the FESLF strain group. The TcpYI protein shares considerable sequence homology to members of the Toll/IL-1 receptor family. Bacterial TIR domain containing proteins (Tcps) interact with the innate immune system by TIR-TIR interactions and subvert host defenses via individual, multifaceted mechanisms. In terms of virulence, it appears that the TcpYI protein of Y. pseudotuberculosis displays its own virulence phenotype compared to the previously characterized bacterial Tcps. Our results clearly demonstrate that TcpYI increases the intracellular survival of the respective strains in vitro. Furthermore, we show here that the intracellular survival benefit of the wild-type strain correlates with an increase in tcpYI gene expression inside murine macrophages. In support of this, we found that TcpYI enhances the survival inside the spleens of mice in a mouse model of peritonitis. Our results may point toward involvement of the TcpYI protein in inhibition of phagocytosis, particularly in distinct Y. pseudotuberculosis strains of the FESLF strain group where the pYV virulence plasmid is absent.

Thermosensing to adjust bacterial virulence in a fluctuating environment

The lifecycle of most microbial pathogens can be divided into two states: existence outside and inside their hosts. The sudden temperature upshift experienced upon entry from environmental or vector reservoirs into a warm-blooded host is one of the most crucial signals informing the pathogens to adjust virulence gene expression and their host-stress survival program. This article reviews the plethora of sophisticated strategies that bacteria have evolved to sense temperature, and outlines the molecular signal transduction mechanisms used to modulate synthesis of crucial virulence determinants. The molecular details of thermal control through conformational changes of DNA, RNA and proteins are summarized, complex and diverse thermosensing principles are introduced and their potential as drug targets or synthetic tools are discussed.

Genotypic Characterization of Yersinia enterocolitica Biotype 4/O:3 Isolates from Pigs and Slaughterhouses Using SE-AFLP, ERIC-PCR, and PFGE

Yersinia enterocolitica is a foodborne pathogen that causes illness in humans and animals. The biotype 4/O:3 has been commonly associated with yersiniosis and is characterized by the presence of chromosomal and extra-chromosomal virulence genes. Molecular typing methods have been successfully used to characterize Y. enterocolitica genetic heterogeneity and to study the epidemiology of the bacteria from different origins. In this study, 320 Y. enterocolitica biotype 4/O:3 isolates originating in pigs and slaughterhouses were characterized according to the virulence profile, and 61 isolates were typified through SE-AFLP, ERIC-PCR, and PFGE techniques. The majority of the isolates originated from pigs, and the predominant virulence profile was ail+ virF+ rfbC+ ystA+, representing 83.4% of the tested isolates. All of the Y. enterocolitica 4/O:3 isolates were positive for at least ystA gene. The SE-AFLP and ERIC-PCR patterns were highly homogeneous. The SE-AFLP was more discriminative than the ERIC-PCR and tended to cluster isolates according to the slaughterhouse. Despite the limited genetic diversity of Y. enterocolitica 4/O:3, PFGE was shown to be the most discriminative technique considering one band of difference. Fattening pigs proved to be an important reservoir of Y. enterocolitica biotype 4/O:3 carrying virulence genes.

A phenotype at last: essential role for the Yersinia enterocolitica Ysa type III secretion system in a Drosophila melanogaster S2 cell model

The highly pathogenic Yersinia enterocolitica strains have a chromosomally encoded type III secretion system (T3SS) that is expressed and functional in vitro only when the bacteria are cultured at 26 °C. Mutations that render this system nonfunctional are slightly attenuated in the mouse model of infection only following an oral inoculation and only at early time points postinfection. The discrepancy between the temperature required for the Ysa gene expression and the physiological temperature required for mammalian model systems has made defining the role of this T3SS challenging. Therefore, we explored the use of Drosophila S2 cells as a model system for studying Ysa function. We show here that Y. enterocolitica is capable of infecting S2 cells and replicating intracellularly to high levels, an unusual feature of this pathogen. Importantly, we show that the Ysa T3SS is required for robust intracellular replication. A secretion-deficient mutant lacking the secretin gene, ysaC, is defective in replication within S2 cells, marking the first demonstration of a pronounced Ysa-dependent virulence phenotype. Establishment of S2 cells as a model for Y. enterocolitica infection provides a versatile tool to elucidate the role of the Ysa T3SS in the life cycle of this gastrointestinal pathogen.

A mutant with aberrant extracellular LcrV-YscF interactions fails to form pores and translocate Yop effector proteins but retains the ability to trigger Yop secretion in response to host cell contact

The plasmid-encoded type three secretion system (TTSS) of Yersinia spp. is responsible for the delivery of effector proteins into cells of the innate immune system, where these effectors disrupt the target cells' activity. Successful translocation of effectors into mammalian cells requires Yersinia to both insert a translocon into the host cell membrane and sense contact with host cells. To probe the events necessary for translocation, we investigated protein-protein interactions among TTSS components of the needle-translocon complex using a chemical cross-linking-based approach. We detected extracellular protein complexes containing YscF, LcrV, and YopD that were dependent upon needle formation. The formation of these complexes was evaluated in a secretion-competent but translocation-defective mutant, the YscFD28AD46A strain (expressing YscF with the mutations D28A and D46A). We found that one of the YscF and most of the LcrV and YopD cross-linked complexes were nearly absent in this mutant. Furthermore, the YscFD28AD46A strain did not support YopB insertion into mammalian membranes, supporting the idea that the LcrV tip complex is required for YopB insertion and translocon formation. However, the YscFD28AD46A strain did secrete Yops in the presence of host cells, indicating that a translocation-competent tip complex is not required to sense contact with host cells to trigger Yop secretion. In conclusion, in the absence of cross-linkable LcrV-YscF interactions, translocon insertion is abolished, but Yersinia still retains the ability to sense cell contact.

Characterization of Yersinia enterocolitica biotype 1A strains isolated from swine slaughterhouses and markets

Yersinia enterocolitica is an important foodborne pathogen that causes illness in humans and animals. Y. enterocolitica is also the most heterogeneous species of the genus and is divided into distinct serotypes and over six biotypes. Y. enterocolitica biotype 1A strains are classically considered as nonpathogenic; however, some biotype 1A isolates have been considered as causative of gastrointestinal disease, yielding symptoms indistinguishable from those produced by pathogenic biotypes. Even after decades of isolation of clinical strains, the pathogenic mechanisms of these isolates are still not fully understood. In the present study, 122 Yersinia enterocolitica biotype 1A strains isolated from swine slaughterhouses and meat markets in Sao Paulo, Brazil, were characterized according to the presence of the virulence genes ail, virF, and ystA. A total of 94 strains were positive to at least one virulence gene (77.05%), and 67 were positive to all of them (54.92%). Twenty-two strains were submitted to PFGE genotyping resulting in 22 distinct pulsotypes, varying from 50% to 84% of genetic similarity. Any clustering tendency among pulsotypes related to origin, isolation site, or even virulence profile was not observed. The present study reports an important contamination of the environment in swine slaughterhouses, meat markets, and pork, by potentially virulent Y. enterocolitica biotype 1A.

Inheritance of the lysozyme inhibitor Ivy was an important evolutionary step by Yersinia pestis to avoid the host innate immune response

BACKGROUND

Yersinia pestis (the plague bacillus) and its ancestor, Yersinia pseudotuberculosis (which causes self-limited bowel disease), encode putative homologues of the periplasmic lysozyme inhibitor Ivy and the membrane-bound lysozyme inhibitor MliC. The involvement of both inhibitors in virulence remains subject to debate.

METHODS

Mutants lacking ivy and/or mliC were generated. We evaluated the mutants' ability to counter lysozyme, grow in serum, and/or counter leukocytes; to produce disease in wild-type, neutropenic, or lysozyme-deficient rodents; and to induce host inflammation.

RESULTS

MliC was not required for lysozyme resistance and the development of plague. Deletion of ivy decreased Y. pestis' ability to counter lysozyme and polymorphonuclear neutrophils, but it did not affect the bacterium's ability to grow in serum or resist macrophages. Y. pestis lacking Ivy had attenuated virulence, unless animals were neutropenic or lysozyme deficient. The Ivy mutant induced inflammation to a degree similar to that of the parental strain. Last, Y. pseudotuberculosis did not require Ivy to counter lysozyme and for virulence.

CONCLUSIONS

Ivy is required to counter lysozyme during infection, but its role as a virulence factor is species dependent. Our study also shows that a gene that is not necessary for the virulence of an ancestral bacterium may become essential in the emergence of a new pathogen.

Pathogenicity of Yersinia pestis synthesis of 1-dephosphorylated lipid A

Synthesis of Escherichia coli LpxL, which transfers a secondary laurate chain to the 2' position of lipid A, in Yersinia pestis produced bisphosphoryl hexa-acylated lipid A at 37°C, leading to significant attenuation of virulence. Our previous observations also indicated that strain χ10015(pCD1Ap) (ΔlpxP32::P(lpxL) lpxL) stimulated a strong inflammatory reaction but sickened mice before recovery and retained virulence via intranasal (i.n.) infection. The development of live, attenuated Y. pestis vaccines may be facilitated by detoxification of its lipopolysaccharide (LPS). Heterologous expression of the lipid A 1-phosphatase, LpxE, from Francisella tularensis in Y. pestis yields predominantly 1-dephosphorylated lipid A, as confirmed by mass spectrometry. Results indicated that expression of LpxE on top of LpxL provided no significant reduction in virulence of Y. pestis in mice when it was administered i.n. but actually reduced the 50% lethal dose (LD(50)) by 3 orders of magnitude when the strain was administered subcutaneously (s.c.). Additionally, LpxE synthesis in wild-type Y. pestis KIM6+(pCD1Ap) led to slight attenuation by s.c. inoculation but no virulence change by i.n. inoculation in mice. In contrast to Salmonella enterica, expression of LpxE does not attenuate the virulence of Y. pestis.

The SycN/YscB chaperone-binding domain of YopN is required for the calcium-dependent regulation of Yop secretion by Yersinia pestis

Numerous Gram-negative bacterial pathogens employ type III secretion systems (T3SSs) to inject effector proteins into eukaryotic cells. The activation of the type III secretion (T3S) process is tightly controlled in all T3SSs. In Yersinia pestis, the secretion of effector proteins, termed Yersinia outer proteins (Yops), is regulated by the activity of the YopN/SycN/YscB/TyeA complex. YopN is a secreted protein that interacts with the SycN/YscB chaperone via an N-terminal chaperone-binding domain (CBD) and with TyeA via a C-terminal TyeA-binding domain (TBD). Efficient YopN secretion is dependent upon its N-terminal secretion signal (SS), CBD, and the SycN/YscB chaperone. In this study, we investigate the role of the YopN CBD in the regulation of Yop secretion. Analysis of YopE/YopN hybrid proteins in which the YopN SS or SS and CBD were replaced with the analogous regions of YopE indicated that the YopN CBD or SycN/YscB chaperone play a role in the regulation of Yop secretion that is independent of their established roles in YopN secretion. To further analyze the role of the YopN CBD in the regulation of Yop secretion a series of tetra-alanine substitution mutants were generated throughout the YopN CBD. A number of these mutants exhibited a defect in the regulation of Yop secretion but showed no defect in YopN secretion or in the interaction of YopN with the SycN/YscB chaperone. Finally, conditions were established that enabled YopN and TyeA to regulate Yop secretion in the absence of the SycN/YscB chaperone. Importantly, a number of the YopN CBD mutants maintained their defect in the regulation of Yop secretion even under the established SycN/YscB chaperone-independent conditions. These studies establish a role for the CBD region of YopN in the regulation of Yop secretion that is independent from its role in YopN secretion or in the binding of the SycN/YscB chaperone.

Identification of novel protein-protein interactions of Yersinia pestis type III secretion system by yeast two hybrid system

Type III secretion system (T3SS) of the plague bacterium Y. pestis encodes a syringe-like structure consisting of more than 20 proteins, which can inject virulence effectors into host cells to modulate the cellular functions. Here in this report, interactions among the possible components in T3SS of Yersinia pestis were identified using yeast mating technique. A total of 57 genes, including all the pCD1-encoded genes except those involved in plasmid replication and partition, pseudogenes, and the putative transposase genes, were subjected to yeast mating analysis. 21 pairs of interaction proteins were identified, among which 9 pairs had been previously reported and 12 novel pairs were identified in this study. Six of them were tested by GST pull down assay, and interaction pairs of YscG-SycD, YscG-TyeA, YscI-YscF, and YopN-YpCD1.09c were successfully validated, suggesting that these interactions might play potential roles in function of Yersinia T3SS. Several potential new interactions among T3SS components could help to understand the assembly and regulation of Yersinia T3SS.

Type III secretion translocon assemblies that attenuate Yersinia virulence

Type III secretion enables bacteria to intoxicate eukaryotic cells with anti-host effectors. A class of secreted cargo are the two hydrophobic translocators that form a translocon pore in the host cell plasma membrane through which the translocated effectors may gain cellular entry. In pathogenic Yersinia, YopB and YopD shape this translocon pore. Here, four in cis yopD mutations were constructed to disrupt a predicted α-helix motif at the C-terminus. Mutants YopD(I262P) and YopD(K267P) poorly localized Yop effectors into target eukaryotic cells and failed to resist uptake and killing by immune cells. These defects were due to deficiencies in host-membrane insertion of the YopD-YopB translocon. Mutants YopDA(263P) and YopD(A270P) had no measurable in vitro translocation defect, even though they formed smaller translocon pores in erythrocyte membranes. Despite this, all four mutants were attenuated in a mouse infection model. Hence, YopD variants have been generated that can spawn translocons capable of targeting effectors in vitro, yet were bereft of any lethal effect in vivo. Therefore, Yop translocators may possess other in vivo functions that extend beyond being a portal for effector delivery into host cells.