Identification of Chlamydia trachomatis outer membrane complex proteins by differential proteomics

Comparison of cysteine content in whole proteomes across the three domains of life

An empirical observation suggests that Giardia lamblia proteins have larger cysteine content than their counterparts in other organisms. As this parasite lacks conventional antioxidant stress systems, it is generally accepted that high cysteine content helps G. lamblia cope with oxygen toxicity, a strategy apparently shared by other organisms. Here, we question whether the high cysteine content in some organisms is genuine or just a simple assumption based on singular observations. To this end, we analyzed the cysteine content in 78 proteomes of organisms spanning the three domains of life. The results indicate that the cysteine content in eukaryota is approximately double that in archaea and bacteria, with G. lamblia among the highest. Atypical cysteine contents were found in a few organisms correlating with specific environmental conditions, supporting the evolutionary amino acid-level selection of amino acid composition.

Repeat infections with chlamydia in women may be more transcriptionally active with lower responses from some immune genes

Chlamydia trachomatis, the most common bacterial sexually transmitted infection worldwide, is responsible for considerable health burden due to its significant sequelae. There are growing concerns about chlamydial treatment and management due to widely documented increasing burden of repeat infections. In the current study, a cohort study design of 305 women with urogenital chlamydial infections demonstrated that 11.8% of women experienced repeat infections after treatment with azithromycin. The chlamydial DNA load measured by quantitative PCR was higher in women who experienced a repeat infection (p = 0.0097) and repeat infection was associated with sexual contact. There was no genomic or phenotypic evidence of azithromycin resistance within the chlamydial isolates. During repeat infection, or repeat positive tests during follow up, vaginal chlamydial gene expression (ompA, euo, omcB, htrA, trpAB) was markedly higher compared to baseline, and two of the selected immune genes analyzed had significantly lower expression at the time of repeat infection. Overall, there are two implications of these results. The results could be generalized to all recent infections, or repeat positive events, and indicate that chlamydial infections are have higher transcriptional activity of select genes early in the infection in women. Alternatively, after azithromycin treatment, repeat infections of Chlamydia may be more transcriptionally active at certain genes, and there may be post-treatment immunological alterations that interplay into repeat exposures establishing an active infection. The potential that recent infections may involve a higher level of activity from the organism may have implications for management by more regular testing of the most at risk women to reduce the risk of sequelae.

Characterization of Chlamydia muridarum TC0668 Protein: Localization, Expression, and Inflammation-Inducing Effects on Host Cell

The objective of this study is to elucidate the basic biological properties and function of TC0668 in vitro. Laser confocal microscopy and immune-electron microscopy were used to detect localization of TC0668 in Chlamydia-infected human epithelial cells, while the expression phase was investigated by qRT-PCR and western blot analysis. Protein array technology was employed to evaluate differences in cytokine secretion between cells infected with tc0668 single mutants and those infected with tc0668 null mutants. We found that TC0668 is restricted to the chlamydial inclusion. Translation and transcription of TC0668 were detected at 4 h and peaked at 16 h during the life cycle of Chlamydia in vitro. The cytokines produced by tc0668 single mutant infected cultures compared with tc0668 null mutant group indicated that 36 cytokines were downregulated, while 10 were up-regulated significantly. C. muridarum bearing a single tc0668 gene mutation have decreased urogenital pathogenicity that is explained by the effects of the mutation on the regulation of inflammation-related cytokine secretion.

Overexpression of the Bam Complex Improves the Production of Chlamydia trachomatis MOMP in the E. coli Outer Membrane

A licensed Chlamydia trachomatis (Ct) vaccine is not yet available. Recombinant Chlamydia trachomatis major outer membrane protein (Ct-MOMP), the most abundant constituent of the chlamydial outer membrane complex, is considered the most attractive candidate for subunit-based vaccine formulations. Unfortunately, Ct-MOMP is difficult to express in its native structure in the E. coli outer membrane (OM). Here, by co-expression of the Bam complex, we improved the expression and localization of recombinant Ct-MOMP in the E. coli OM. Under these conditions, recombinant Ct-MOMP appeared to assemble into a β-barrel conformation and express domains at the cell surface indicative of correct folding. The data indicate that limited availability of the Bam complex can be a bottleneck for the production of heterologous OM vaccine antigens, information that is also relevant for strategies aimed at producing recombinant OMV-based vaccines.

Chlamydia trachomatis Polymorphic Membrane Proteins (Pmps) Form Functional Homomeric and Heteromeric Oligomers

Chlamydiae are Gram-negative, obligate intracellular bacteria, which infect animals and humans. Adhesion to host cells, the first step in the infection process, is mediated by polymorphic membrane proteins (Pmps). Pmps constitute the largest chlamydial protein family, with 9 members (subdivided into six subtypes) in C. trachomatis and 21 in C. pneumoniae, and are characterized by the presence of multiple copies of GGA(I,L,V) and FxxN motifs. Motif-rich fragments of all nine C. trachomatis Pmps act as adhesins and are essential for infection. As autotransporters, most Pmp proteins are secreted through their β-barrel domain and localize on the surface of the chlamydial cell, where most of them are proteolytically processed. Classical autotransporters are monomeric proteins, which can function as toxins, proteases, lipases and monoadhesive adhesins. Here we show that selected recombinant C. trachomatis Pmp fragments form functional adhesion-competent multimers. They assemble into homomeric and heteromeric filaments, as revealed by non-denaturing gel electrophoresis, size-exclusion chromatography and electron microscopy. Heteromeric filaments reach 2 μm in length, significantly longer than homomeric structures. Filament formation was independent of the number of motifs present in the fragment(s) concerned and their relative affinity for host cells. Our functional studies demonstrated that only adhesion-competent oligomers were able to block a subsequent infection. Pre-loading of infectious chlamydial cells with adhesion-competent Pmp oligomers maintained the subsequent infection, while adhesion-incompetent structures reduced infectivity, presumably by blocking the function of endogenous Pmps. The very large number of possible heteromeric and homomeric Pmp complexes represents a novel mechanism to ensure stable adhesion and possibly host cell immune escape.

Chlamydia overcomes multiple gastrointestinal barriers to achieve long-lasting colonization

Chlamydia trachomatis (CT) is frequently detected in the human gastrointestinal (GI) tract despite its leading role in sexually transmitted bacterial infections in the genital tract. Chlamydia muridarum (CM), a model pathogen for investigating CT pathogenesis in the genital tract, can also colonize the mouse GI tract for long periods. Genital-tract mutants of CM no longer colonize the GI tract. The mutants lacking plasmid functions are more defective in colonizing the upper GI tract while certain chromosomal gene-deficient mutants are more defective in the lower GI tract, suggesting that Chlamydia may use the plasmid for promoting its spread to the large intestine while using the chromosome-encoded factors for maintaining its colonization in the large intestine. The plasmid-encoded Pgp3 is critical for Chlamydia to resist the acid barrier in the stomach and to overcome a CD4⁺ T cell barrier in the small intestine. On reaching the large intestine, Pgp3 is no longer required. Instead, the chromosome-encoded open reading frames TC0237/TC0668 become essential for Chlamydia to evade the group 3-like innate lymphoid cell-secreted interferon (IFN)γ in the large intestine. These findings are important for exploring the medical significance of chlamydial colonization in the gut and for understanding the mechanisms of chlamydial pathogenicity in the genital tract.

Super-Resolution Fluorescence Microscopy Reveals Clustering Behaviour of Chlamydia pneumoniae's Major Outer Membrane Protein

Chlamydia pneumoniae is a Gram-negative bacterium responsible for a number of human respiratory diseases and linked to some chronic inflammatory diseases. The major outer membrane protein (MOMP) of Chlamydia is a conserved immunologically dominant protein located in the outer membrane, which, together with its surface exposure and abundance, has led to MOMP being the main focus for vaccine and antimicrobial studies in recent decades. MOMP has a major role in the chlamydial outer membrane complex through the formation of intermolecular disulphide bonds, although the exact interactions formed are currently unknown. Here, it is proposed that due to the large number of cysteines available for disulphide bonding, interactions occur between cysteine-rich pockets as opposed to individual residues. Such pockets were identified using a MOMP homology model with a supporting low-resolution (~4 Å) crystal structure. The localisation of MOMP in the E. coli membrane was assessed using direct stochastic optical reconstruction microscopy (dSTORM), which showed a decrease in membrane clustering with cysteine-rich regions containing two mutations. These results indicate that disulphide bond formation was not disrupted by single mutants located in the cysteine-dense regions and was instead compensated by neighbouring cysteines within the pocket in support of this cysteine-rich pocket hypothesis.

Sigma 54-Regulated Transcription Is Associated with Membrane Reorganization and Type III Secretion Effectors during Conversion to Infectious Forms of Chlamydia trachomatis

The factors that control the growth and infectious processes for Chlamydia are still poorly understood. This study used recently developed genetic tools to determine the regulon for one of the key transcription factors encoded by Chlamydia, sigma 54. Surrogate and computational analyses provide additional support for the hypothesis that sigma 54 plays a key role in controlling the expression of many components critical to converting and enabling the infectious capability of Chlamydia. These components include those that remodel the membrane for the extracellular environment and incorporation of an arsenal of type III secretion effectors in preparation for infecting new cells.

Chlamydia bacteria are obligate intracellular organisms with a phylum-defining biphasic developmental cycle that is intrinsically linked to its ability to cause disease. The progression of the chlamydial developmental cycle is regulated by the temporal expression of genes predominantly controlled by RNA polymerase sigma (σ) factors. Sigma 54 (σ⁵⁴) is one of three sigma factors encoded by Chlamydia for which the role and regulon are unknown. CtcC is part of a two-component signal transduction system that is requisite for σ⁵⁴ transcriptional activation. CtcC activation of σ⁵⁴ requires phosphorylation, which relieves inhibition by the CtcC regulatory domain and enables ATP hydrolysis by the ATPase domain. Prior studies with CtcC homologs in other organisms have shown that expression of the ATPase domain alone can activate σ⁵⁴ transcription. Biochemical analysis of CtcC ATPase domain supported the idea of ATP hydrolysis occurring in the absence of the regulatory domain, as well as the presence of an active-site residue essential for ATPase activity (E242). Using recently developed genetic approaches in Chlamydia to induce expression of the CtcC ATPase domain, a transcriptional profile was determined that is expected to reflect the σ⁵⁴ regulon. Computational evaluation revealed that the majority of the differentially expressed genes were preceded by highly conserved σ⁵⁴ promoter elements. Reporter gene analyses using these putative σ⁵⁴ promoters reinforced the accuracy of the model of the proposed regulon. Investigation of the gene products included in this regulon supports the idea that σ⁵⁴ controls expression of genes that are critical for conversion of Chlamydia from replicative reticulate bodies into infectious elementary bodies.

Comparison of Chlamydia outer membrane complex to recombinant outer membrane proteins as vaccine

The Chlamydial outer membrane complex (COMC) from the elementary body (EB) is a protein rich insoluble outer membrane shell from which cytosolic proteins have been extracted with detergent. In this study we conducted mass spectrometry experiments to detect proteins in the COMC prepared from C. muridarum EB. Proteomic analysis showed that the COMC contained 75 proteins that included 10 outer membrane proteins (OMPs) such as the major outer membrane protein (MOMP) and polymorphic membrane proteins (Pmps) that were previously identified as CD4 T cell vaccine candidates. We tested the vaccine efficacy of COMC in comparison to individual or combination of recombinant OMPs formulated with Th1 polarizing adjuvant DDA/MPL in two murine genital tract models (C. muridarum and C. trachomatis) by measuring organismal shedding, tubal pathology and immune responses including neutralizing antibodies. In the C. muridarum model, the COMC vaccine generated broadly reactive immune responses against multiple outer membrane proteins, high levels of EB binding and neutralizing antibody and exhibited superior protection against genital infection and pathology when compared to the recombinant PmpG vaccine. Denaturing the COMC by boiling significantly reduced protection. In the C. trachomatis model, the COMC vaccine also conferred greater protection compared to individual or multiple recombinant outer membrane proteins. Immunization with multiple COMCs from C. trachomatis serovars D, F and J generated neutralizing antibodies against multiple C. trachomatis serovars. We conclude that broader immunogenicity and generation of neutralizing antibody may explain the superior efficacy of COMC vaccine. The study suggests that conformationally intact proteins will be necessary for a successful recombinant OMP vaccine.

Chlamydia: what is on the outside does matter

This review summarises major highlights on the structural biology of the chlamydial envelope. Chlamydiae are obligate intracellular bacteria, characterised by a unique biphasic developmental cycle. Depending on the stage of their lifecycle, they appear in the form of elementary or reticulate bodies. Since these particles have distinctive functions, it is not surprising that their envelope differs in lipid as well as in protein content. Vice versa, by identifying surface proteins, specific characteristics of the particles such as rigidity or immunogenicity may be deduced. Detailed information on the bacterial membranes will increase our understanding on the host-pathogen interactions chlamydiae employ to survive and grow and might lead to new strategies to battle chlamydial infections.

Comparison of motif-based and whole-unique-sequence-based analyses of phage display library datasets generated by biopanning of anti-Borrelia burgdorferi immune sera

Detection of protection-associated epitopes via reverse vaccinology is the first step for development of subunit vaccines against microbial pathogens. Mapping subunit vaccine targets requires high throughput methods, which would allow delineation of epitopes recognized by protective antibodies on a large scale. Phage displayed random peptide library coupled to Next Generation Sequencing (PDRPL/NGS) is the universal platform that enables high-yield identification of peptides that mimic epitopes (mimotopes). Despite being unsurpassed as a tool for discovery of polyclonal serum mimotopes, the PDRPL/NGS is far inferior as a quantitative method of immune response. Difficult-to-control fluctuations in amounts of antibody-bound phages after rounds of selection and amplification diminish the quantitative capacity of the PDRPL/NGS. In an attempt to improve the accuracy of the PDRPL/NGS method, we compared the discriminating capacity of two approaches for PDRPL/NGS data analysis. The whole-unique-sequence-based analysis (WUSA) involved generation of 7-mer peptide profiles and comparison of the numbers of sequencing reads for unique peptide sequences between serum samples. The motif-based analysis (MA) included identification of 4-mer consensus motifs unifying unique 7-mer sequences and comparison of motifs between serum samples. The motif comparison was based not on the numbers of sequencing reads, but on the numbers of distinct 7-mers constituting the motifs. Our PDRPL/NGS datasets generated from biopanning of protective and non-protective anti-Borrelia burgdorferi sera of New Zealand rabbits were used to contrast the two approaches. As a result, the principle component analyses (PCA) showed that the discriminating powers of the WUSA and MA were similar. In contrast, the unsupervised hierarchical clustering obtained via the MA classified the preimmune, non-protective, and protective sera better than the WUSA-based clustering. Also, a total number of discriminating motifs was higher than that of discriminating 7-mers. In sum, our results indicate that MA approach improves the accuracy and quantitative capacity of the PDRPL/NGS method.

Spectroscopic analysis of chlamydial major outer membrane protein in support of structure elucidation

Chlamydial major outer membrane protein (MOMP) is the major protein constituent of the bacterial pathogen Chlamydia trachomatis. Chlamydia trachomatis Serovars D–K are the leading cause of genital tract infections which can lead to infertility or ectopic pregnancies. A vaccine against Chlamydia is highly desirable but currently not available. MOMP accounts for ~ 60% of the chlamydial protein mass and is considered to be one of the lead vaccine candidates against C. trachomatis. We report on the spectroscopic analysis of C. trachomatis native MOMP Serovars D, E, F, and J as well as C. muridarum MOMP by size exclusion chromatography multi angle light scattering (SEC MALS), circular dichroism (CD) and attenuated total reflectance Fourier transform infrared spectroscopy (ATR‐FTIR). MOMP was purified from the native bacterium grown in either adherent HeLa cells or in different suspension cell lines. Our results confirm that MOMP forms homo‐trimers in detergent micelles. The secondary structure composition of C. trachomatis MOMP was conserved across serovars, but different from composition of C. muridarum MOMP with a 13% (CD) to 18% (ATR‐FTIR) reduction in β‐sheet conformation for C. trachomatis MOMP. When Serovar E MOMP was isolated from suspension cell lines the α‐helix content increased by 7% (CD) to 13% (ATIR‐FTIR). Maintenance of a native‐like tertiary and quaternary structure in subunit vaccines is important for the generation of protective antibodies. This biophysical characterization of MOMP presented here serves, in the absence of functional assays, as a method for monitoring the structural integrity of MOMP.

Proteomic characterisation of the Chlamydia abortus outer membrane complex (COMC) using combined rapid monolithic column liquid chromatography and fast MS/MS scanning

Data are presented on the identification and partial characterisation of proteins comprising the chlamydial outer membrane complex (COMC) fraction of Chlamydia abortus (C. abortus)—the aetiological agent of ovine enzootic abortion. Inoculation with the COMC fraction is known to be highly effective in protecting sheep against experimental challenge and its constituent proteins are therefore of interest as potential vaccine candidates. Sodium N-lauroylsarcosine (sarkosyl) insoluble COMC proteins resolved by SDS-PAGE were interrogated by mass spectrometry using combined rapid monolithic column liquid chromatography and fast MS/MS scanning. Downstream database mining of processed tandem MS data revealed the presence of 67 proteins in total, including putative membrane associated proteins (n = 36), such as porins, polymorphic membrane proteins (Pmps), chaperonins and hypothetical membrane proteins, in addition to others (n = 22) that appear more likely to have originated from other subcellular compartments. Electrophoretic mobility data combined with detailed amino acid sequence information derived from secondary fragmentation spectra for 8 Pmps enabled peptides originating from protein cleavage fragments to be mapped to corresponding regions of parent precursor molecules yielding preliminary evidence in support of endogenous post-translational processing of outer membrane proteins in C. abortus. The data presented here will facilitate a deeper understanding of the pathogenesis of C. abortus infection and represent an important step towards the elucidation of the mechanisms of immunoprotection against C. abortus infection and the identification of potential target vaccine candidate antigens.

Chlamydial Infection From Outside to Inside

Chlamydia are obligate intracellular bacteria, characterized by a unique biphasic developmental cycle. Specific interactions with the host cell are crucial for the bacteria’s survival and amplification because of the reduced chlamydial genome. At the start of infection, pathogen-host interactions are set in place in order for Chlamydia to enter the host cell and reach the nutrient-rich peri-Golgi region. Once intracellular localization is established, interactions with organelles and pathways of the host cell enable the necessary hijacking of host-derived nutrients. Detailed information on the aforementioned processes will increase our understanding on the intracellular pathogenesis of chlamydiae and hence might lead to new strategies to battle chlamydial infection. This review summarizes how chlamydiae generate their intracellular niche in the host cell, acquire host-derived nutrients in order to enable their growth and finally exit the host cell in order to infect new cells. Moreover, the evolution in the development of molecular genetic tools, necessary for studying the chlamydial infection biology in more depth, is discussed in great detail.

The multiple functions of the numerous Chlamydia trachomatis secreted proteins: the tip of the iceberg

Chlamydia trachomatis serovars are obligate intracellular bacterial pathogens mainly causing ocular and urogenital infections that affect millions of people worldwide and which can lead to blindness or sterility. They reside and multiply intracellularly within a membrane-bound vacuolar compartment, known as inclusion, and are characterized by a developmental cycle involving two morphologically and physiologically distinct chlamydial forms. Completion of the developmental cycle involves the secretion of > 70 C. trachomatis proteins that function in the host cell cytoplasm and nucleus, in the inclusion membrane and lumen, and in the extracellular milieu. These proteins can, for example, interfere with the host cell cytoskeleton, vesicular and non-vesicular transport, metabolism, and immune signalling. Generally, this promotes C. trachomatis invasion into, and escape from, host cells, the acquisition of nutrients by the chlamydiae, and evasion of cell-autonomous, humoral and cellular innate immunity. Here, we present an in-depth review on the current knowledge and outstanding questions about these C. trachomatis secreted proteins.

Distinct Roles of Chromosome- versus Plasmid-Encoded Genital Tract Virulence Factors in Promoting Chlamydia muridarum Colonization in the Gastrointestinal Tract

The genital pathogen Chlamydia is known to colonize the gastrointestinal tract. Orally delivered Chlamydia muridarum can reach the colon and maintain a long-lasting colonization there. However, C. muridarum with mutations in chromosomal genes tc0237 and tc0668 (designated a chromosomal mutant) or deficient in plasmid-encoded pGP3 (designated a plasmid mutant) is unable to do so. We now report that the chromosomal mutant is still able to reach the colon while the plasmid mutant fails to do so following an oral delivery, suggesting that lack of colon colonization by different mutants may involve distinct mechanisms. Consistently, a direct intracolonic delivery selectively restored the ability of the plasmid mutant, but not the chromosomal mutant, to colonize the colon. The chromosomal mutant was rescued only in the colon of mice deficient in gamma interferon (IFN-γ). Thus, the chromosomal mutant's deficiency in colonizing colonic mucosal tissue is likely due to its increased susceptibility to IFN-γ-mediated immunity. Furthermore, IFN-γ deficiency was sufficient for rescuing colon colonization of an orally delivered chromosomal mutant but not plasmid mutant while mice deficient in gastric acid production rescued the plasmid mutant but not the chromosomal mutant. Both mutants are attenuated in inducing genital tract pathology. Thus, we propose that chlamydial chromosomal-gene-encoded genital tract virulence factors may be essential for Chlamydia to maintain long-lasting colonization in the colon while the plasmid may enable Chlamydia to reach the colon by promoting evasion of gastric barriers.

Delineating Surface Epitopes of Lyme Disease Pathogen Targeted by Highly Protective Antibodies of New Zealand White Rabbits

Lyme disease (LD), the most prevalent vector-borne illness in the United States and Europe, is caused by Borreliella burgdorferi No vaccine is available for humans. Dogmatically, B. burgdorferi can establish a persistent infection in the mammalian host (e.g., mice) due to a surface antigen, VlsE. This antigenically variable protein allows the spirochete to continually evade borreliacidal antibodies. However, our recent study has shown that the B. burgdorferi spirochete is effectively cleared by anti-B. burgdorferi antibodies of New Zealand White rabbits, despite the surface expression of VlsE. Besides homologous protection, the rabbit antibodies also cross-protect against heterologous B. burgdorferi spirochetes and significantly reduce the pathology of LD arthritis in persistently infected mice. Thus, this finding that NZW rabbits develop a unique repertoire of very potent antibodies targeting the protective surface epitopes, despite abundant VlsE, prompted us to identify the specificities of the protective rabbit antibodies and their respective targets. By applying subtractive reverse vaccinology, which involved the use of random peptide phage display libraries coupled with next-generation sequencing and our computational algorithms, repertoires of nonprotective (early) and protective (late) rabbit antibodies were identified and directly compared. Consequently, putative surface epitopes that are unique to the protective rabbit sera were mapped. Importantly, the relevance of newly identified protection-associated epitopes for their surface exposure has been strongly supported by prior empirical studies. This study is significant because it now allows us to systematically test the putative epitopes for their protective efficacy with an ultimate goal of selecting the most efficacious targets for development of a long-awaited LD vaccine.

Sequencing the Obligate Intracellular Rhabdochlamydia helvetica within Its Tick Host Ixodes ricinus to Investigate Their Symbiotic Relationship

The Rhabdochlamydiaceae family is one of the most widely distributed within the phylum Chlamydiae, but most of its members remain uncultivable. Rhabdochlamydia 16S rRNA was recently reported in more than 2% of 8,534 pools of ticks from Switzerland. Shotgun metagenomics was performed on a pool of five female Ixodes ricinus ticks presenting a high concentration of chlamydial DNA, allowing the assembly of a high-quality draft genome. About 60% of sequence reads originated from a single bacterial population that was named "Candidatus Rhabdochlamydia helvetica" whereas only few thousand reads mapped to the genome of "Candidatus Midichloria mitochondrii," a symbiont normally observed in all I. ricinus females. The 1.8 Mbp genome of R. helvetica is smaller than other Chlamydia-related bacteria. Comparative analyses with other chlamydial genomes identified transposases of the PD-(D/E)XK nuclease family that are unique to this new genome. These transposases show evidence of interphylum horizontal gene transfers between multiple arthropod endosymbionts, including Cardinium spp. (Bacteroidetes) and diverse proteobacteria such as Wolbachia, Rickettsia spp. (Rickettsiales), and Caedimonas varicaedens (Holosporales). Bacterial symbionts were previously suggested to provide B-vitamins to hematophagous hosts. However, incomplete metabolic capacities including for B-vitamin biosynthesis, high bacterial density and limited prevalence suggest that R. helvetica is parasitic rather than symbiotic to its host. The identification of novel Rhabdochlamydia strains in different hosts and their sequencing will help understanding if members of this genus have become highly specialized parasites with reduced genomes, like the Chlamydiaceae, or if they could be pathogenic to humans using ticks as a transmission vector.

Genetic Screen in Chlamydia muridarum Reveals Role for an Interferon-Induced Host Cell Death Program in Antimicrobial Inclusion Rupture

Multiple obligatory intracellular bacteria in the genus Chlamydia are important pathogens. In humans, strains of C. trachomatis cause trachoma, chlamydia, and lymphogranuloma venereum. These diseases are all associated with extended courses of infection and reinfection that likely reflect the ability of chlamydiae to evade various aspects of host immune responses. Interferon-stimulated genes, driven in part by the cytokine interferon gamma, restrict the host range of various Chlamydia species, but how these pathogens evade interferon-stimulated genes in their definitive host is poorly understood. Various Chlamydia species can inhibit death of their host cells and may have evolved this strategy to evade prodeath signals elicited by host immune responses. We present evidence that chlamydia-induced programmed cell death resistance evolved to counter interferon- and immune-mediated killing of Chlamydia-infected cells.

Interferon-regulated immune defenses protect mammals from pathogenically diverse obligate intracellular bacterial pathogens of the genus Chlamydia. Interferon gamma (IFN-γ) is especially important in controlling the virulence of Chlamydia species and thus impacts the modeling of human chlamydial infection and disease in mice. How IFN-γ contributes to cell-autonomous defenses against Chlamydia species and how these pathogens evade IFN-γ-mediated immunity in their natural hosts are not well understood. We conducted a genetic screen which identified 31 IFN-γ-sensitive (Igs) mutants of the mouse model pathogen Chlamydia muridarum. Genetic suppressor analysis and lateral gene transfer were used to map the phenotype of one of these mutants, Igs4, to a missense mutation in a putative chlamydial inclusion membrane protein, TC0574. We observed the lytic destruction of Igs4-occupied inclusions and accompanying host cell death in response to IFN-γ priming or various proapoptotic stimuli. However, Igs4 was insensitive to IFN-γ-regulated cell-autonomous defenses previously implicated in anti-Chlamydia trachomatis host defense in mice. Igs4 inclusion integrity was restored by caspase inhibitors, indicating that the IFN-γ-mediated destruction of Igs4 inclusions is dependent upon the function of caspases or related prodeath cysteine proteases. We further demonstrated that the Igs4 mutant is immune restricted in an IFN-γ-dependent manner in a mouse infection model, thereby implicating IFN-γ-mediated inclusion destruction and host cell death as potent in vivo host defense mechanisms to which wild-type C. muridarum is resistant. Overall, our results suggest that C. muridarum evolved resistance mechanisms to counter IFN-γ-elicited programmed cell death and the associated destruction of intravacuolar pathogens.

Life inside and out: making and breaking protein disulfide bonds in Chlamydia

Disulphide bonds are widely used among all domains of life to provide structural stability to proteins and to regulate enzyme activity. Chlamydia spp. are obligate intracellular bacteria that are especially dependent on the formation and degradation of protein disulphide bonds. Members of the genus Chlamydia have a unique biphasic developmental cycle alternating between two distinct cell types; the extracellular infectious elementary body (EB) and the intracellular replicating reticulate body. The proteins in the envelope of the EB are heavily cross-linked with disulphides and this is known to be critical for this infectious phase. In this review, we provide a comprehensive summary of what is known about the redox state of chlamydial envelope proteins throughout the developmental cycle. We focus especially on the factors responsible for degradation and formation of disulphide bonds in Chlamydia and how this system compares with redox regulation in other organisms. Focussing on the unique biology of Chlamydia enables us to provide important insights into how specialized suites of disulphide bond (Dsb) proteins cater for specific bacterial environments and lifecycles.

Applying lessons from human papillomavirus vaccines to the development of vaccines against Chlamydia trachomatis

INTRODUCTION

Chlamydia trachomatis (Ct), the most common bacterial sexually transmitted infection (STI), leads to pelvic inflammatory disease, infertility, and ectopic pregnancy in women. In this Perspective, we discuss the successful human papillomavirus (HPV) vaccine as a case study to inform Ct vaccine efforts. Areas covered: The immunological basis of HPV vaccine-elicited protection is high-titer, long-lasting antibody responses in the genital tract which provides sterilizing immunity. These antibodies are elicited through parenteral administration of a subunit vaccine based on virus-like particles (VLPs) of HPV. We present three lessons learned from the successful HPV vaccine efforts: (1) antibodies alone can be sufficient to provide protection from STIs in the genital tract, (2) the successful generation of high antibody levels is due to the multivalent structure of HPV VLPs, (3) major challenges exist in designing vaccines that elicit appropriate effector T cells in the genital tract. We then discuss the possibility of antibody-based immunity for Ct. Expert commentary: In this Perspective, we present a case for developing antibody-eliciting vaccines, similar to the HPV vaccine, for Ct. Basic research into the mechanisms of Ct entry into host cells will reveal new vaccine targets, which may be antigens against which antibodies are not normally elicited during natural infection.

Virulence-related comparative transcriptomics of infectious and non-infectious chlamydial particles

BACKGROUND

Members of the phylum Chlamydiae are obligate intracellular pathogens of humans and animals and have a serious impact on host health. They comprise several zoonotic species with varying disease outcomes and prevalence. To investigate differences in virulence, we focused on Chlamydia psittaci, C. abortus and Waddlia chondrophila. Most threatening is C. psittaci, which frequently infects humans and causes psittacosis associated with severe pneumonia. The closest relative of C. psittaci is C. abortus, which shares the vast majority of genes but less frequently infects humans, and causes stillbirth and sepsis. W. chondrophila is more distantly related, and occasional human infections are associated with respiratory diseases or miscarriage. One possible explanation for differences in virulence originate from species-specific genes as well as differentially expressed homologous virulence factors.

RESULTS

RNA-sequencing (RNA-Seq) was applied to purified infectious elementary bodies (EBs) and non-infectious reticulate bodies (RBs) in order to elucidate the transcriptome of the infectious and replicative chlamydial states. The results showed that approximately half of all genes were differentially expressed. For a descriptive comparison, genes were categorised according to their function in the RAST database. This list was extended by the inclusion of inclusion membrane proteins, outer membrane proteins, polymorphic membrane proteins and type III secretion system effectors. In addition, the expression of fifty-six known and a variety of predicted virulence and immunogenic factors with homologs in C. psittaci, C. abortus and W. chondrophila was analysed. To confirm the RNA-Seq results, the expression of nine factors was validated using real-time quantitative polymerase chain reaction (RT-qPCR). Comparison of RNA-Seq and RT-qPCR results showed a high mean Pearson correlation coefficient of 0.95.

CONCLUSIONS

It was shown that both the replicative and infectious chlamydial state contained distinctive transcriptomes and the cellular processes emphasised in EBs and RBs differed substantially based on the chlamydial species. In addition, the very first interspecies transcriptome comparison is presented here, and the considerable differences in expression of homologous virulence factors might contribute to the differing infection rates and disease outcomes of the pathogens. The RNA-Seq results were confirmed by RT-qPCR and demonstrate the feasibility of interspecies transcriptome comparisons in chlamydia.

Surface enhanced Raman spectroscopy of Chlamydia trachomatis and Neisseria gonorrhoeae for diagnostics, and extra-cellular metabolomics and biochemical monitoring

SERS spectra excited at 785 nm of the bacteria Chlamydia trahomatis (elementary bodies, EB) and Neisseria gonorrheoae, the causative pathogens for the two most common sexually transmitted diseases (STD), chlamydia and gonorrhea, respectively, are reported. Although both are Gram-negative bacteria, the SERS signatures of C. trachomatis and N. gonorrheoae are completely different. N. gonorrheoae SERS spectra are due to the starvation induced nucleotide metabolites adenine and guanine, and the surface associated co-enzyme nicotinamide adenine dinucleotide and are very similar on Au and Ag although the spectrum appears more rapidly on Ag. The C. trachomatis SERS spectrum is dominated by the vibrational features of cell surface proteins. While features attributable to specific residues and the amide backbone characterize the C. trachomatis spectrum on Ag, the corresponding SERS spectrum on Au substrates displays vibrational characteristics of aggregated proteins. The prospects for the development of a SERS based platform for rapid (<one hour), low-cost bacterial STD diagnostics are promising based on these initial studies. Furthermore, this biomedical application demonstrates the potential for SERS to be a sensitive real time probe of the dynamics of biochemical activity in the cell wall and extracellular regions of microorganisms.

Population-based analysis of ocular Chlamydia trachomatis in trachoma-endemic West African communities identifies genomic markers of disease severity

BACKGROUND

Chlamydia trachomatis (Ct) is the most common infectious cause of blindness and bacterial sexually transmitted infection worldwide. Ct strain-specific differences in clinical trachoma suggest that genetic polymorphisms in Ct may contribute to the observed variability in severity of clinical disease.

METHODS

Using Ct whole genome sequences obtained directly from conjunctival swabs, we studied Ct genomic diversity and associations between Ct genetic polymorphisms with ocular localization and disease severity in a treatment-naïve trachoma-endemic population in Guinea-Bissau, West Africa.

RESULTS

All Ct sequences fall within the T2 ocular clade phylogenetically. This is consistent with the presence of the characteristic deletion in trpA resulting in a truncated non-functional protein and the ocular tyrosine repeat regions present in tarP associated with ocular tissue localization. We have identified 21 Ct non-synonymous single nucleotide polymorphisms (SNPs) associated with ocular localization, including SNPs within pmpD (odds ratio, OR = 4.07, p* = 0.001) and tarP (OR = 0.34, p* = 0.009). Eight synonymous SNPs associated with disease severity were found in yjfH (rlmB) (OR = 0.13, p* = 0.037), CTA0273 (OR = 0.12, p* = 0.027), trmD (OR = 0.12, p* = 0.032), CTA0744 (OR = 0.12, p* = 0.041), glgA (OR = 0.10, p* = 0.026), alaS (OR = 0.10, p* = 0.032), pmpE (OR = 0.08, p* = 0.001) and the intergenic region CTA0744-CTA0745 (OR = 0.13, p* = 0.043).

CONCLUSIONS

This study demonstrates the extent of genomic diversity within a naturally circulating population of ocular Ct and is the first to describe novel genomic associations with disease severity. These findings direct investigation of host-pathogen interactions that may be important in ocular Ct pathogenesis and disease transmission.

Chlamydia Spreading from the Genital Tract to the Gastrointestinal Tract - A Two-Hit Hypothesis

Chlamydia trachomatis, a leading bacterial cause of sexually transmitted infection-induced infertility, is frequently detected in the gastrointestinal tract. Chlamydia muridarum, a model pathogen for investigating C. trachomatis pathogenesis, readily spreads from the mouse genital tract to the gastrointestinal tract, establishing long-lasting colonization. C. muridarum mutants, despite their ability to activate acute oviduct inflammation, are attenuated in inducing tubal fibrosis and are no longer able to colonize the gastrointestinal tract, suggesting that the spread of C. muridarum to the gastrointestinal tract may contribute to its pathogenicity in the upper genital tract. However, gastrointestinal C. muridarum cannot directly autoinoculate the genital tract. Both antigen-specific CD8⁺ T cells and profibrotic cytokines, such as TNFα and IL-13, are essential for C. muridarum to induce tubal fibrosis; this may be induced by the gastrointestinal C. muridarum, as a second hit, to transmucosally convert tubal repairing - initiated by C. muridarum infection of tubal epithelial cells (serving as the first hit) - into pathogenic fibrosis. Testing the two-hit mouse model should both add new knowledge to the growing list of mechanisms by which gastrointestinal microbes contribute to pathologies in extragastrointestinal tissues and provide information for investigating the potential role of gastrointestinal C. trachomatis in human chlamydial pathogenesis.

Chlamydia muridarum with Mutations in Chromosomal Genes tc0237 and/or tc0668 Is Deficient in Colonizing the Mouse Gastrointestinal Tract

Chlamydiae colonize the gastrointestinal tracts of both animals and humans. However, their medical significance remains unknown. We have previously shown that wild-type Chlamydia muridarum spreads to and establishes stable colonization of the gastrointestinal tract following intravaginal inoculation. In the present study, we found that C. muridarum with mutations in chromosomal genes tc0237 and/or tc0668 was defective in spreading to the mouse gastrointestinal tract, which correlated with its attenuated pathogenicity in the upper genital tract. This correlation was more consistent than that of chlamydial pathogenicity with ascending infection in the genital tract, since attenuated C. muridarum spread significantly less to the gastrointestinal tract but maintained robust ascending infection of the upper genital tract. Transcervical inoculation further confirmed the correlation between C. muridarum spreading to the gastrointestinal tract and its pathogenicity in the upper genital tract. Finally, defective spreading of C. muridarum mutants was due to their inability to colonize the gastrointestinal tract since intragastric inoculation did not rescue the mutants' colonization. Thus, promoting C. muridarum colonization of the gastrointestinal tract may represent a primary function of the TC0237 and TC0668 proteins. Correlation of chlamydial colonization of the gastrointestinal tract with chlamydial pathogenicity in the upper genital tract suggests a potential role for gastrointestinal chlamydiae in genital tract pathogenicity.

Impact of antiseptics on Chlamydia trachomatis growth

Bacterial vaginosis is a frequent dysbiosis, where the normal lactobacillus-dominated flora is replaced by an anaerob/aerob polymicrobial flora. Bacterial vaginosis increases the risk of acquiring sexually transmitted infections (STI) including the most frequent Chlamydia trachomatis infections. Intravaginal antiseptics are part of the bacterial vaginosis treatment, and ideally they should also inhibit the bacterial vaginosis-related STI. Therefore, we tested the antichlamydial activity of four antiseptics: iodine aqueous solution, povidone-iodine, chlorhexidine and borax. First, we measured the impact of antiseptics on the viability of the HeLa cervical epithelial cells, and calculated the maximum nontoxic concentrations. Next, we infected the cells with C. trachomatis preincubated for 1 h with the particular antiseptic. The chlamydial growth was measured by direct quantitative PCR (qPCR) of the infected cells. The minimal inhibitory concentrations (MIC) of chlorhexidine and povidone-iodine were 3·91 and 97 μg ml(-1) respectively; however, the MIC of chlorhexidine was close to its maximum nontoxic concentration. The iodine aqueous solution and the borax showed no antichlamydial activity. Our in vitro studies showed that chlorhexidine and particularly povidone-iodine are potentially able to limit the bacterial vaginosis-related C. trachomatis infection.

SIGNIFICANCE AND IMPACT OF THE STUDY

We measured the antichlamydial effects of various antiseptics. These antiseptics are being used for the treatment of bacterial vaginosis, but their effect on the bacterial vaginosis-related sexually transmitted infections, particularly the most frequent Chlamydia trachomatis (C. trachomatis) infections has not been investigated. We showed that povidone-iodine (Betadine) inhibited the chlamydial growth in concentrations that was not toxic to the epithelial cells. We concluded that due to its additional antichlamydial effect, povidone-iodine could be a preferable antiseptic in bacterial vaginosis treatment.

Update on Chlamydia trachomatis Vaccinology

Attempts to produce a vaccine to protect against Chlamydia trachomatis-induced trachoma were initiated more than 100 years ago and continued for several decades. Using whole organisms, protective responses were obtained. However, upon exposure to C. trachomatis, disease exacerbation developed in some immunized individuals, precluding the implementation of the vaccine. Evidence of the role of C. trachomatis as a sexually transmitted pathogen started to emerge in the 1960s, and it soon became evident that it can cause acute infections and long-term sequelae in women, men, and newborns. The main focus of this minireview is to summarize recent findings and discuss formulations, including antigens, adjuvants, routes, and delivery systems for immunization, primarily explored in the female mouse model, with the goal of implementing a vaccine against C. trachomatis genital infections.

The Predominant CD4+ Th1 Cytokine Elicited to Chlamydia trachomatis Infection in Women Is Tumor Necrosis Factor Alpha and Not Interferon Gamma

Chlamydia trachomatis infection is the most prevalent bacterial sexually transmitted infection and can cause significant reproductive morbidity in women. There is insufficient knowledge of C. trachomatis-specific immune responses in humans, which could be important in guiding vaccine development efforts. In contrast, murine models have clearly demonstrated the essential role of T helper type 1 (Th1) cells, especially interferon gamma (IFN-γ)-producing CD4⁺ T cells, in protective immunity to chlamydia. To determine the frequency and magnitude of Th1 cytokine responses elicited to C. trachomatis infection in humans, we stimulated peripheral blood mononuclear cells from 90 chlamydia-infected women with C. trachomatis elementary bodies, Pgp3, and major outer membrane protein and measured IFN-γ-, tumor necrosis factor alpha (TNF-α)-, and interleukin-2 (IL-2)-producing CD4⁺ and CD8⁺ T-cell responses using intracellular cytokine staining. The majority of chlamydia-infected women elicited CD4⁺ TNF-α responses, with frequency and magnitude varying significantly depending on the C. trachomatis antigen used. CD4⁺ IFN-γ and IL-2 responses occurred infrequently, as did production of any of the three cytokines by CD8⁺ T cells. About one-third of TNF-α-producing CD4⁺ T cells coproduced IFN-γ or IL-2. In summary, the predominant Th1 cytokine response elicited to C. trachomatis infection in women was a CD4⁺ TNF-α response, not CD4⁺ IFN-γ, and a subset of the CD4⁺ TNF-α-positive cells produced a second Th1 cytokine.

Profiling and validation of individual and patterns of Chlamydia trachomatis-specific antibody responses in trachomatous trichiasis

BACKGROUND

Ocular Chlamydia trachomatis (Ct) infection causes trachoma, the leading infectious cause of blindness. A Ct D/UW3 proteome microarray and sera from Gambian adults with trachomatous trichiasis (TT) or healthy matched controls previously identified several novel antigens, which suggested differential recognition in adults with TT.

METHODS

We re-analysed this serological microarray data using more robust microarray analysis techniques accounting for typical problems associated with highly dimensional data. We examined the Ct-specific antibody profile concerning the overall diversity of responses, antigen expression stage and cellular localisation of antigens. We tested differentially recognised antigens by further serological testing of the screened sera and used larger independent sample sets for validation.

RESULTS

Antibody responses identified High-Performance on antigens expressed early and late in the Ct developmental cycle and those secreted or localised to the outer membrane. Eight antigens were preferentially recognised by scarred individuals and one antigen by healthy individuals. Three of these antigens, two associated with scarring (CT667 and CT706) and one healthy-associated (CT442), were not associated with the presence or absence of scarring following specific serological testing of the arrayed sera and sera from larger, independent case-control cohorts.

CONCLUSIONS

This study identified focussed Ct-specific antibody profiles targeting proteins expressed during entry and exit from cells and localised to interact with the host. A small panel of antibody responses could discriminate between adults with and without TT in a trachoma-endemic community. Heterogenous responses in the independent validation of these antibody targets highlighted the need for large sample sizes, clearly defined clinical phenotypes and follow-up work.

Analysis of Polymorphic Membrane Protein Expression in Cultured Cells Identifies PmpA and PmpH of Chlamydia psittaci as Candidate Factors in Pathogenesis and Immunity to Infection

The polymorphic membrane protein (Pmp) paralogous families of Chlamydia trachomatis, Chlamydia pneumoniae and Chlamydia abortus are putative targets for Chlamydia vaccine development. To determine whether this is also the case for Pmp family members of C. psittaci, we analyzed transcription levels, protein production and localization of several Pmps of C. psittaci. Pmp expression profiles were characterized using quantitative real-time PCR (RT-qPCR), immunofluorescence (IF) and immuno-electron microscopy (IEM) under normal and stress conditions. We found that PmpA was highly produced in all inclusions as early as 12 hpi in all biological replicates. In addition, PmpA and PmpH appeared to be unusually accessible to antibody as determined by both immunofluorescence and immuno-electron microscopy. Our results suggest an important role for these Pmps in the pathogenesis of C. psittaci, and make them promising candidates in vaccine development.

Interrogating Genes That Mediate Chlamydia trachomatis Survival in Cell Culture Using Conditional Mutants and Recombination

Intracellular bacterial pathogens in the family Chlamydiaceae are causes of human blindness, sexually transmitted disease, and pneumonia. Genetic dissection of the mechanisms of chlamydial pathogenicity has been hindered by multiple limitations, including the inability to inactivate genes that would prevent the production of elementary bodies. Many genes are also Chlamydia-specific genes, and chlamydial genomes have undergone extensive reductive evolution, so functions often cannot be inferred from homologs in other organisms. Conditional mutants have been used to study essential genes of many microorganisms, so we screened a library of 4,184 ethyl methanesulfonate-mutagenized Chlamydia trachomatis isolates for temperature-sensitive (TS) mutants that developed normally at physiological temperature (37°C) but not at nonphysiological temperatures. Heat-sensitive TS mutants were identified at a high frequency, while cold-sensitive mutants were less common. Twelve TS mutants were mapped using a novel markerless recombination approach, PCR, and genome sequencing. TS alleles of genes that play essential roles in other bacteria and chlamydia-specific open reading frames (ORFs) of unknown function were identified. Temperature-shift assays determined that phenotypes of the mutants manifested at distinct points in the developmental cycle. Genome sequencing of a larger population of TS mutants also revealed that the screen had not reached saturation. In summary, we describe the first approach for studying essential chlamydial genes and broadly applicable strategies for genetic mapping in Chlamydia spp. and mutants that both define checkpoints and provide insights into the biology of the chlamydial developmental cycle.

IMPORTANCE

Study of the pathogenesis of Chlamydia spp. has historically been hampered by a lack of genetic tools. Although there has been recent progress in chlamydial genetics, the existing approaches have limitations for the study of the genes that mediate growth of these organisms in cell culture. We used a genetic screen to identify conditional Chlamydia mutants and then mapped these alleles using a broadly applicable recombination strategy. Phenotypes of the mutants provide fundamental insights into unexplored areas of chlamydial pathogenesis and intracellular biology. Finally, the reagents and approaches we describe are powerful resources for the investigation of these organisms.

Quantitative Proteomics of the Infectious and Replicative Forms of Chlamydia trachomatis

The obligate intracellular developmental cycle of Chlamydia trachomatis presents significant challenges in defining its proteome. In this study we have applied quantitative proteomics to both the intracellular reticulate body (RB) and the extracellular elementary body (EB) from C. trachomatis. We used C. trachomatis L2 as a model chlamydial isolate for our study since it has a high infectivity:particle ratio and there is an excellent quality genome sequence. EBs and RBs (>99% pure) were quantified by chromosomal and plasmid copy number using PCR, from which the concentrations of chlamydial proteins per bacterial cell/genome were determined. RBs harvested at 15h post infection (PI) were purified by three successive rounds of gradient centrifugation. This is the earliest possible time to obtain purified RBs, free from host cell components in quantity, within the constraints of the technology. EBs were purified at 48h PI. We then used two-dimensional reverse phase UPLC to fractionate RB or EB peptides before mass spectroscopic analysis, providing absolute amount estimates of chlamydial proteins. The ability to express the data as molecules per cell gave ranking in both abundance and energy requirements for synthesis, allowing meaningful identification of rate-limiting components. The study assigned 562 proteins with high confidence and provided absolute estimates of protein concentration for 489 proteins. Interestingly, the data showed an increase in TTS capacity at 15h PI. Most of the enzymes involved in peptidoglycan biosynthesis were detected along with high levels of muramidase (in EBs) suggesting breakdown of peptidoglycan occurs in the non-dividing form of the microorganism. All the genome-encoded enzymes for glycolysis, pentose phosphate pathway and tricarboxylic acid cycle were identified and quantified; these data supported the observation that the EB is metabolically active. The availability of detailed, accurate quantitative proteomic data will be invaluable for investigations into gene regulation and function.

One Face of Chlamydia trachomatis: The Infectious Elementary Body

The lifestyle of Chlamydiae is unique: the bacteria alternate between two morphologically distinct forms, an infectious non-replicative elementary body (EB), and a replicative, non-infectious reticulate body (RB). This review focuses on recent advances in understanding the structure and function of the infectious form of the best-studied member of the phylum, the human pathogen Chlamydia trachomatis. Once considered as an inert particle of little functional capacity, the EB is now perceived as a sophisticated entity that encounters at least three different environments during each infectious cycle. We review current knowledge on its composition and morphology, and emerging metabolic activities. These features confer resistance to the extracellular environment, the ability to penetrate a host cell and ultimately enable the EB to establish a niche enabling bacterial survival and growth. The bacterial and host molecules involved in these processes are beginning to emerge.

Delivery of a Chlamydial Adhesin N-PmpC Subunit Vaccine to the Ocular Mucosa Using Particulate Carriers

Trachoma, caused by the intracellular bacterium Chlamydia trachomatis (Ct), remains the world's leading preventable infectious cause of blindness. Recent attempts to develop effective vaccines rely on modified chlamydial antigen delivery platforms. As the mechanisms engaged in the pathology of the disease are not fully understood, designing a subunit vaccine specific to chlamydial antigens could improve safety for human use. We propose the delivery of chlamydia-specific antigens to the ocular mucosa using particulate carriers, bacterial ghosts (BGs). We therefore characterized humoral and cellular immune responses after conjunctival and subcutaneous immunization with a N-terminal portion (amino acid 1-893) of the chlamydial polymorphic membrane protein C (PmpC) of Ct serovar B, expressed in probiotic Escherichia coli Nissle 1917 bacterial ghosts (EcN BGs) in BALB/c mice. Three immunizations were performed at two-week intervals, and the immune responses were evaluated two weeks after the final immunization in mice. In a guinea pig model of ocular infection animals were immunized in the same manner as the mice, and protection against challenge was assessed two weeks after the last immunization. N-PmpC was successfully expressed within BGs and delivery to the ocular mucosa was well tolerated without signs of inflammation. N-PmpC-specific mucosal IgA levels in tears yielded significantly increased levels in the group immunized via the conjunctiva compared with the subcutaneously immunized mice. Immunization with N-PmpC EcN BGs via both immunization routes prompted the establishment of an N-PmpC-specific IFNγ immune response. Immunization via the conjunctiva resulted in a decrease in intensity of the transitional inflammatory reaction in conjunctiva of challenged guinea pigs compared with subcutaneously and non-immunized animals. The delivery of the chlamydial subunit vaccine to the ocular mucosa using a particulate carrier, such as BGs, induced both humoral and cellular immune responses. Further investigations are needed to improve the immunization scheme and dosage.

The Chromosome-Encoded Hypothetical Protein TC0668 Is an Upper Genital Tract Pathogenicity Factor of Chlamydia muridarum

We previously associated a missense mutation of the tc0668 gene of serial in vitro-passaged Chlamydia muridarum, a murine model of human urogenital C. trachomatis, with severely attenuated disease development in the upper genital tract of female mice. Since these mutants also contained a TC0237 Q117E missense mutation that enhances their in vitro infectivity, an effort was made here to isolate and characterize a tc0668 single mutant to determine its individual contribution to urogenital pathogenicity. Detailed genetic analysis of C. muridarum passages revealed a truncated variant with a G216* nonsense mutation of the 408-amino-acid TC0668 protein that does not produce a detectable product. Intracellular growth and infectivity of C. muridarum in vitro remain unaffected in the absence of TC0668. Intravaginal inoculation of the TC0668 null mutant into C3H/HeJ mice results in a typical course of lower genital tract infection but, unlike a pathogenic isogenic control, is unable to elicit significant chronic inflammation of the oviduct and fails to induce hydrosalpinx. Thus, TC0668 is demonstrated as an important chromosome-encoded urogenital pathogenicity factor of C. muridarum and the first with these characteristics to be discovered for a Chlamydia pathogen.

In vitro passage selects for Chlamydia muridarum with enhanced infectivity in cultured cells but attenuated pathogenicity in mouse upper genital tract

Although modern Chlamydia muridarum has been passaged for decades, there are no reports on the consequences of serial passage with strong selection pressure on its fitness. In order to explore the potential for Pasteurian selection to induce genomic and phenotypic perturbations to C. muridarum, a starter population was passaged in cultured cells for 28 generations without standard infection assistance. The resultant population, designated CMG28, displays markedly reduced in vitro dependence on centrifugation for infection and low incidence and severity of upper genital tract pathology following intravaginal inoculation into mice compared to the parental C. muridarum population, CMG0. Deep sequencing of CMG0 and CMG28 revealed novel protein variants in the hypothetical genes TC0237 (Q117E) and TC0668 (G322R). In vitro attachment assays of isogenic plaque clone pairs with mutations in either TC0237 and TC0668 or only TC0237 reveal that TC0237(Q117E) is solely responsible for enhanced adherence to host cells. Paradoxically, double mutants, but not TC0237(Q117E) single mutants, display severely attenuated in vivo pathogenicity. These findings implicate TC0237 and TC0668 as novel genetic factors involved in chlamydial attachment and pathogenicity, respectively, and show that serial passage under selection pressure remains an effective tool for studying Chlamydia pathogenicity.

Rapid identification and quantitative validation of a caffeine-degrading pathway in Pseudomonas sp. CES

Understanding the genes and enzymes involved in caffeine metabolism can lead to applications such as production of methylxanthines and environmental waste remediation. Pseudomonas sp. CES may provide insights into these applications, since this bacterium degrades caffeine and thrives in concentrations of caffeine that are three times higher (9.0 g L(-1)) than the maximum tolerable levels of other reported bacteria. We took a novel approach toward identifying the enzymatic pathways in Pseudomonas sp. CES that metabolize caffeine, which largely circumvented the need for exhaustive isolation of enzymes and the stepwise reconstitution of their activities. Here we describe an optimized, rapid alternative strategy based on multiplexed LC-MS/MS assays and show its application by discovering caffeine-degrading enzymes in the CES strain based on quantitative comparison of proteomes from bacteria grown in the absence and presence of caffeine, the latter condition of which was found to have a highly induced capacity for caffeine degradation. Comparisons were made using stable isotope dimethyl labeling, differences in the abundance of particular proteins were substantiated by reciprocal labeling experiments, and the role of the identified proteins in caffeine degradation was independently verified by genetic sequencing. Overall, multiple new components of a N-demethylase system were identified that resulted in rapid pathway validation and gene isolation using this new approach.

The transcriptional repressor EUO regulates both subsets of Chlamydia late genes

The pathogenic bacterium Chlamydia replicates in a eukaryotic host cell via a developmental cycle marked by temporal waves of gene expression. We have previously shown that late genes transcribed by the major chlamydial RNA polymerase, σ(66) RNA polymerase, are regulated by a transcriptional repressor EUO. We now report that EUO also represses promoters for a second subset of late genes that are transcribed by an alternative polymerase called σ(28) RNA polymerase. EUO bound in the vicinity of six σ(28) -dependent promoters and inhibited transcription of each promoter. We used a mutational analysis to demonstrate that the EUO binding site functions as an operator that is necessary and sufficient for EUO-mediated repression of σ(28) -dependent transcription. We also verified specific binding of EUO to σ(66) -dependent and σ(28) -dependent promoters with a DNA immunoprecipitation assay. These findings support a model in which EUO represses expression of both σ(66) -dependent and σ(28) -dependent late genes. We thus propose that EUO is the master regulator of late gene expression in the chlamydial developmental cycle.

Membrane vesicle production by Chlamydia trachomatis as an adaptive response

Bacteria have evolved specific adaptive responses to cope with changing environments. These adaptations include stress response phenotypes with dynamic modifications of the bacterial cell envelope and generation of membrane vesicles (MVs). The obligate intracellular bacterium, Chlamydia trachomatis, typically has a biphasic lifestyle, but can enter into an altered growth state typified by morphologically aberrant chlamydial forms, termed persistent growth forms, when induced by stress in vitro. How C. trachomatis can adapt to a persistent growth state in host epithelial cells in vivo is not well understood, but is an important question, since it extends the host-bacterial relationship in vitro and has thus been indicated as a survival mechanism in chronic chlamydial infections. Here, we review recent findings on the mechanistic aspects of bacterial adaptation to stress with a focus on how C. trachomatis remodels its envelope, produces MVs, and the potential important consequences of MV production with respect to host-pathogen interactions. Emerging data suggest that the generation of MVs may be an important mechanism for C. trachomatis intracellular survival of stress, and thus may aid in the establishment of a chronic infection in human genital epithelial cells.

Nitropropenyl benzodioxole, an anti-infective agent with action as a protein tyrosine phosphatase inhibitor

We report on the activities of a broad spectrum antimicrobial compound,nitropropenyl benzodioxole (NPBD) which are of relevance to its potential as an anti-infective drug. These investigations support the proposal that a major mechanism of NPBD is action as a tyrosine mimetic, competitively inhibiting bacterial and fungal protein tyrosine phosphatases (PTP). NPBD did not affect major anti-bacterial drug targets, namely, ATP production, cell wall or cell membrane integrity, or transcription and translation of RNA. NPBD inhibited bacterial YopH and human PTP1B and not human CD45 in enzyme assays. NPBD inhibited PTP-associated bacterial virulence factors, namely, endospore formation in Bacillus cereus, prodigiosin secretion in Serratia marcescens , motility in Proteus spp., and adherence and invasion of mammalian cells by Yersinia enterocolitica . NPBD acts intracellularly to inhibit the early development stages of the Chlamydia trachomatis infection cycle in mammalian cells known to involve sequestration of host cell PTPs. NPBD thus both kills pathogens and inhibits virulence factors relevant to early infection, making it a suitable candidate for development as an anti-infective agent, particularly for pathogens that enter through, or cause infections at, mucosal surfaces. Though much is yet to be understood about bacterial PTPs, they are proposed as suitable anti-infective targets and have been linked to agents similar to NPBD. The structural and functional diversity and heterogeneous distribution of PTPs across microbial species make them suitably selective targets for the development of both broadly active and pathogen-specific drugs.

Chlamydial MACPF protein CT153

Chlamydiae are obligate intracellular bacterial parasites that infect a wide range of metazoan hosts. Some Chlamydia species are important causes of chronic inflammatory diseases of the ocular, genital and respiratory tracts in humans. Genes located in a variable region of chlamydial genomes termed the plasticity zone are known to be key determinants of pathogenic diversity. The plasticity zone protein CT153, present only in select species, contains a membrane attack complex/perforin (MACPF) domain, which may mediate chlamydial interactions with the host cell. CT153 is present throughout the C. trachomatis developmental cycle and is processed into polypeptides that interact with membranes differently than does the parent protein. Chlamydiae interact extensively with membranes from the time of invasion until they eventually exit host cells, so numerous roles for a MACPF protein in pathogenesis of these pathogens are conceivable. Here, we present an overview of what is known about CT153 and highlight potential roles of a MACPF family protein in a group of pathogens whose intracellular development is marked by a series of interactions with host cell membranes and organelles. Finally, we identify new strategies for identifying CT153 functions made feasible by the recent development of a basic toolset for genetic manipulation of chlamydiae.

Vaccines, reverse vaccinology, and bacterial pathogenesis

Advances in genomics and innovative strategies such as reverse vaccinology have changed the concepts and approaches to vaccine candidate selection and design. Genome mining and blind selection of novel antigens provide a novel route to investigate the mechanisms that underpin pathogenesis. The resulting lists of novel candidates are revealing new aspects of pathogenesis of target organisms, which in turn drives the rational design of optimal vaccine antigens. Here we use the discovery, characterization, and exploitation of fHbp, a vaccine candidate and key virulence factor of meningococcus, as an illustrative case in point. Applying genomic approaches to study both the pathogen and host will ultimately increase our fundamental understanding of pathogen biology, mechanisms responsible for the development of protective immunity, and guide next-generation vaccine design.

Protein-protein interaction networks: probing disease mechanisms using model systems

Protein-protein interactions (PPIs) and multi-protein complexes perform central roles in the cellular systems of all living organisms. In humans, disruptions of the normal patterns of PPIs and protein complexes can be causative or indicative of a disease state. Recent developments in the biological applications of mass spectrometry (MS)-based proteomics have expanded the horizon for the application of systematic large-scale mapping of physical interactions to probe disease mechanisms. In this review, we examine the application of MS-based approaches for the experimental analysis of PPI networks and protein complexes, focusing on the different model systems (including human cells) used to study the molecular basis of common diseases such as cancer, cardiomyopathies, diabetes, microbial infections, and genetic and neurodegenerative disorders.

Chlamydia trachomatis control requires a vaccine

As the most common reported communicable disease in North America and Europe, Chlamydia trachomatis is the focus of concerted public health control efforts based on screening and treatment. Unexpectedly control efforts are accompanied by rising reinfection rates attributed in part to arresting the development of herd immunity. Shortening the duration of infection through the testing and treatment program is the root cause behind the arrested immunity hypothesis and because of this a vaccine will be essential to control efforts. Advances in Chlamydia vaccinomics have revealed the C. trachomatis antigens that can be used to constitute a subunit vaccine and a vaccine solution appears to be scientifically achievable. We propose that an accelerated C. trachomatis vaccine effort requires coordinated partnership among academic, public health and private sector players together with a commitment to C. trachomatis vaccine control as a global public health priority.

Identification and characterization of a novel porin family highlights a major difference in the outer membrane of chlamydial symbionts and pathogens

The Chlamydiae constitute an evolutionary well separated group of intracellular bacteria comprising important pathogens of humans as well as symbionts of protozoa. The amoeba symbiont Protochlamydia amoebophila lacks a homologue of the most abundant outer membrane protein of the Chlamydiaceae, the major outer membrane protein MOMP, highlighting a major difference between environmental chlamydiae and their pathogenic counterparts. We recently identified a novel family of putative porins encoded in the genome of P. amoebophila by in silico analysis. Two of these Protochlamydiaouter membrane proteins, PomS (pc1489) and PomT (pc1077), are highly abundant in outer membrane preparations of this organism. Here we show that all four members of this putative porin family are toxic when expressed in the heterologous host Escherichia coli. Immunofluorescence analysis using antibodies against heterologously expressed PomT and PomS purified directly from elementary bodies, respectively, demonstrated the location of both proteins in the outer membrane of P. amoebophila. The location of the most abundant protein PomS was further confirmed by immuno-transmission electron microscopy. We could show that pomS is transcribed, and the corresponding protein is present in the outer membrane throughout the complete developmental cycle, suggesting an essential role for P. amoebophila. Lipid bilayer measurements demonstrated that PomS functions as a porin with anion-selectivity and a pore size similar to the Chlamydiaceae MOMP. Taken together, our results suggest that PomS, possibly in concert with PomT and other members of this porin family, is the functional equivalent of MOMP in P. amoebophila. This work contributes to our understanding of the adaptations of symbiotic and pathogenic chlamydiae to their different eukaryotic hosts.

Chlamydial biology and its associated virulence blockers

Chlamydiales are obligate intracellular parasites of eukaryotic cells. They can be distinguished from other Gram-negative bacteria through their characteristic developmental cycle, in addition to special biochemical and physical adaptations to subvert the eukaryotic host cell. The host spectrum includes humans and other mammals, fish, birds, reptiles, insects and even amoeba, causing a plethora of diseases. The first part of this review focuses on the specific chlamydial infection biology and metabolism. As resistance to classical antibiotics is emerging among Chlamydiae as well, the second part elaborates on specific compounds and tools to block chlamydial virulence traits, such as adhesion and internalization, Type III secretion and modulation of gene expression.

The early gene product EUO is a transcriptional repressor that selectively regulates promoters of Chlamydia late genes

The obligate intracellular bacterium Chlamydia has an unusual developmental cycle in which there is conversion between two forms that are specialized for either intracellular replication or propagation of the infection to a new host cell. Expression of late chlamydial genes is upregulated during conversion from the replicating to the infectious form, but the mechanism for this temporal regulation is unknown. We found that EUO, which is expressed from an early gene, binds to two sites upstream of the late operon omcAB, but only the downstream site was necessary for transcriptional repression. Using gel shift and in vitro transcription assays we showed that EUO specifically bound and repressed promoters of Chlamydia trachomatis late genes, but not early or mid genes. These findings support a role for EUO as a temporal repressor that negatively regulates late chlamydial genes and prevents their premature expression. The basis of this specificity is the ability of EUO to selectively bind promoter regions of late genes, which would prevent their transcription by RNA polymerase. Thus, we propose that EUO is a master regulator that prevents the terminal differentiation of the replicating form of chlamydiae into the infectious form until sufficient rounds of replication have occurred.