Electron Microscopic Observations on the Fine Structure of Cell Walls of Chlamydia psittaci

Altering the redox status of Chlamydia trachomatis directly impacts its developmental cycle progression

Chlamydia trachomatis is an obligate intracellular bacterial pathogen with a unique developmental cycle. It differentiates between two functional and morphological forms: the elementary body (EB) and the reticulate body (RB). The signals that trigger differentiation from one form to the other are unknown. EBs and RBs have distinctive characteristics that distinguish them, including their size, infectivity, proteome, and transcriptome. Intriguingly, they also differ in their overall redox status as EBs are oxidized and RBs are reduced. We hypothesize that alterations in redox may serve as a trigger for secondary differentiation. To test this, we examined the function of the primary antioxidant enzyme alkyl hydroperoxide reductase subunit C (AhpC), a well-known member of the peroxiredoxins family, in chlamydial growth and development. Based on our hypothesis, we predicted that altering the expression of ahpC would modulate chlamydial redox status and trigger earlier or delayed secondary differentiation. Therefore, we created ahpC overexpression and knockdown strains. During ahpC knockdown, ROS levels were elevated, and the bacteria were sensitive to a broad set of peroxide stresses. Interestingly, we observed increased expression of EB-associated genes and concurrent higher production of EBs at an earlier time in the developmental cycle, indicating earlier secondary differentiation occurs under elevated oxidation conditions. In contrast, overexpression of AhpC created a resistant phenotype against oxidizing agents and delayed secondary differentiation. Together, these results indicate that redox potential is a critical factor in developmental cycle progression. For the first time, our study provides a mechanism of chlamydial secondary differentiation dependent on redox status.

Altering the redox status of Chlamydia trachomatis directly impacts its developmental cycle progression

Chlamydia trachomatis is an obligate intracellular bacterial pathogen with a unique developmental cycle. It differentiates between two functional and morphological forms: elementary body (EB) and reticulate body (RB). The signals that trigger differentiation from one form to the other are unknown. EBs and RBs have distinctive characteristics that distinguish them, including their size, infectivity, proteome, and transcriptome. Intriguingly, they also differ in their overall redox status as EBs are oxidized and RBs are reduced. We hypothesize that alterations in redox may serve as a trigger for secondary differentiation. To test this, we examined the function of the primary antioxidant enzyme alkyl hydroperoxide reductase subunit C (AhpC), a well-known member of the peroxiredoxins family, in chlamydial growth and development. Based on our hypothesis, we predicted that altering the expression of ahpC would modulate chlamydial redox status and trigger earlier or delayed secondary differentiation. To test this, we created ahpC overexpression and knockdown strains. During ahpC knockdown, ROS levels were elevated, and the bacteria were sensitive to a broad set of peroxide stresses. Interestingly, we observed increased expression of EB-associated genes and concurrent higher production of EBs at an earlier time in the developmental cycle, indicating earlier secondary differentiation occurs under elevated oxidation conditions. In contrast, overexpression of AhpC created a resistant phenotype against oxidizing agents and delayed secondary differentiation. Together, these results indicate that redox potential is a critical factor in developmental cycle progression. For the first time, our study provides a mechanism of chlamydial secondary differentiation dependent on redox status.

A comprehensive review on avian chlamydiosis: a neglected zoonotic disease

Avian chlamydiosis is one of the important neglected diseases with critical zoonotic potential. Chlamydia psittaci, the causative agent, affects most categories of birds, livestock, companion animals, and humans. It has many obscured characters and epidemiological dimensions, which makes it unique among other bacterial agents. Recent reports on transmission from equine to humans alarmed the public health authorities, and it necessitates the importance of routine screening of this infectious disease. High prevalence of spill-over infection in equines was associated with reproductive losses. Newer avian chlamydial species are being reported in the recent years. It is a potential biological warfare agent and the disease is an occupational hazard mainly to custom officers handling exotic birds. Prevalence of the disease in wild birds, pet birds, and poultry causes economic losses to the poultry industry and the pet bird trade. Interestingly, there are speculations on the ‘legal’ and ‘illegal’ bird trade that may be the global source of some of the most virulent strains of this pathogen. The mortality rate generally ranges from 5 to 40% in untreated cases, but it can sometimes be higher in co-infection. The intracellular lifestyle of this pathogen makes the diagnosis more complicated and there is also lack of accurate diagnostics. Resistance to antibiotics is reported only in some pathogens of the Chlamydiaceae family, but routine screening may assess the actual situation in all pathogens. Due to the diverse nature of the pathogen, the organism necessitates the One Health partnerships to have complete understanding. The present review focuses on the zoonotic aspects of avian chlamydiosis with its new insights into the pathogenesis, transmission, treatment, prevention, and control strategies. The review also briefs on the basic understandings and complex epidemiology of avian chlamydiosis, highlighting the need for research on emerging one health perspectives.

Penicillin-binding proteins regulate multiple steps in the polarized cell division process of Chlamydia

Chlamydia trachomatis serovar L2 and Chlamydia muridarum, which do not express FtsZ, undergo polarized cell division. During division, peptidoglycan assembles at the pole of dividing Chlamydia trachomatis cells where daughter cell formation occurs, and peptidoglycan regulates at least two distinct steps in the polarized division of Chlamydia trachomatis and Chlamydia muridarum. Cells treated with inhibitors that prevent peptidoglycan synthesis or peptidoglycan crosslinking by penicillin-binding protein 2 (PBP2) are unable to initiate polarized division, while cells treated with inhibitors that prevent peptidoglycan crosslinking by penicillin-binding protein 3 (PBP3/FtsI) initiate polarized division, but the process arrests at an early stage of daughter cell growth. Consistent with their distinct roles in polarized division, peptidoglycan organization is different in cells treated with PBP2 and PBP3-specific inhibitors. Our analyses indicate that the sequential action of PBP2 and PBP3 drives changes in peptidoglycan organization that are essential for the polarized division of these obligate intracellular bacteria. Furthermore, the roles we have characterized for PBP2 and PBP3 in regulating specific steps in chlamydial cell division have not been described in other bacteria.

Beyond Tryptophan Synthase: Identification of Genes That Contribute to Chlamydia trachomatis Survival during Gamma Interferon-Induced Persistence and Reactivation

Chlamydia trachomatis can enter a viable but nonculturable state in vitro termed persistence. A common feature of C. trachomatis persistence models is that reticulate bodies fail to divide and make few infectious progeny until the persistence-inducing stressor is removed. One model of persistence that has relevance to human disease involves tryptophan limitation mediated by the host enzyme indoleamine 2,3-dioxygenase, which converts l-tryptophan to N-formylkynurenine. Genital C. trachomatis strains can counter tryptophan limitation because they encode a tryptophan-synthesizing enzyme. Tryptophan synthase is the only enzyme that has been confirmed to play a role in interferon gamma (IFN-γ)-induced persistence, although profound changes in chlamydial physiology and gene expression occur in the presence of persistence-inducing stressors. Thus, we screened a population of mutagenized C. trachomatis strains for mutants that failed to reactivate from IFN-γ-induced persistence. Six mutants were identified, and the mutations linked to the persistence phenotype in three of these were successfully mapped. One mutant had a missense mutation in tryptophan synthase; however, this mutant behaved differently from previously described synthase null mutants. Two hypothetical genes of unknown function, ctl0225 and ctl0694, were also identified and may be involved in amino acid transport and DNA damage repair, respectively. Our results indicate that C. trachomatis utilizes functionally diverse genes to mediate survival during and reactivation from persistence in HeLa cells.

Characterization of CPAF critical residues and secretion during Chlamydia trachomatis infection

CPAF (chlamydial protease-like activity factor), a Chlamydia serine protease, is activated via proximity-induced intermolecular dimerization that triggers processing and removal of an inhibitory peptide occupying the CPAF substrate-binding groove. An active CPAF is a homodimer of two identical intramolecular heterodimers, each consisting of 29-kDa N-terminal and 35-kDa C-terminal fragments. However, critical residues for CPAF intermolecular dimerization, catalytic activity, and processing were defined in cell-free systems. Complementation of a CPAF-deficient chlamydial organism with a plasmid-encoded CPAF has enabled us to characterize CPAF during infection. The transformants expressing CPAF mutated at intermolecular dimerization, catalytic, or cleavage residues still produced active CPAF, although at a lower efficiency, indicating that CPAF can tolerate more mutations inside Chlamydia-infected cells than in cell-free systems. Only by simultaneously mutating both intermolecular dimerization and catalytic residues was CPAF activation completely blocked during infection, both indicating the importance of the critical residues identified in the cell-free systems and exploring the limit of CPAF's tolerance for mutations in the intracellular environment. We further found that active CPAF was always detected in the host cell cytoplasm while nonactive CPAF was restricted to within the chlamydial inclusions, regardless of how the infected cell samples were treated. Thus, CPAF translocation into the host cell cytoplasm correlates with CPAF enzymatic activity and is not altered by sample treatment conditions. These observations have provided new evidence for CPAF activation and translocation, which should encourage continued investigation of CPAF in chlamydial pathogenesis.

Electron tomography and cryo-SEM characterization reveals novel ultrastructural features of host-parasite interaction during Chlamydia abortus infection

Chlamydia (C.) abortus is a widely spread pathogen among ruminants that can be transmitted to women during pregnancy leading to severe systemic infection with consecutive abortion. As a member of the Chlamydiaceae, C. abortus shares the characteristic feature of an obligate intracellular biphasic developmental cycle with two morphological forms including elementary bodies (EBs) and reticulate bodies (RBs). In contrast to other chlamydial species, C. abortus ultrastructure has not been investigated yet. To do so, samples were fixed by high-pressure freezing and processed by different electron microscopic methods. Freeze-substituted samples were analysed by transmission electron microscopy, scanning transmission electron microscopical tomography and immuno-electron microscopy, and freeze-fractured samples were analysed by cryo-scanning electron microscopy. Here, we present three ultrastructural features of C. abortus that have not been reported up to now. Firstly, the morphological evidence that C. abortus is equipped with the type three secretion system. Secondly, the accumulation and even coating of whole inclusion bodies by membrane complexes consisting of multiple closely adjacent membranes which seems to be a C. abortus specific feature. Thirdly, the formation of small vesicles in the periplasmic space of RBs in the second half of the developmental cycle. Concerning the time point of their formation and the fact that they harbour chlamydial components, these vesicles might be morphological correlates of an intermediate step during the process of redifferentiation of RBs into EBs. As this feature has also been shown for C. trachomatis and C. pneumoniae, it might be a common characteristic of the family of Chlamydiaceae.

A path forward for the chlamydial virulence factor CPAF

CPAF is a conserved and secreted protease from obligate intracellular bacteria of the order Chlamydiales. Recently, it was demonstrated that most of its host targets are an artifact of inaccurate methods. This review aims to summarize key features of CPAF and propose new approaches for evaluating its role in chlamydial pathogenesis.

Antimicrobial effect of natural polyphenols with or without antibiotics on Chlamydia pneumoniae infection in vitro

Chlamydia pneumoniae is a human pathogen that causes multiple diseases worldwide. Despite appropriate therapy with antichlamydial antibiotics, chronic exacerbated diseases often occur and lead to serious sequelae. The use of the macrolide clarithromycin and the fluoroquinolone ofloxacin has improved the treatment of chlamydial infection, but therapy failure is still a major problem. In this work, we studied the pretreatment with natural polyphenols and subsequent treatment with clarithromycin or ofloxacin. The phenolic compounds resveratrol and quercetin improved the antichlamydial effect of clarithromycin and ofloxacin. In particular, resveratrol at 40 μM and quercetin at 20 μM exhibited significant growth inhibition on C. pneumoniae in presence of clarithromycin or ofloxacin compared to controls. In addition, we demonstrated that both resveratrol and quercetin decreased IL-17 and IL-23 production in a time-dependent manner in C. pneumoniae-infected cells. The results showed a particularly strong inhibition of the IL-23 levels released with combined treatment of resveratrol or quercetin and ofloxacin or clarithromycin, suggesting that the combined treatment may afford a synergistic effect in controlling Chlamydia infections.

Innate immune responses to Chlamydia pneumoniae infection: role of TLRs, NLRs, and the inflammasome

Chlamydiae are important human pathogens that are responsible for a wide rage of diseases with a significant impact on public health. In this review article we highlight how recent studies have increased our knowledge of Chlamydia pneumoniae pathogenesis and mechanisms of innate immunity directed host defense against C. pneumoniae infection.

Inhibition of indoleamine 2,3-dioxygenase activity by levo-1-methyl tryptophan blocks gamma interferon-induced Chlamydia trachomatis persistence in human epithelial cells

Gamma interferon (IFN-γ) induces expression of the tryptophan-catabolizing enzyme indoleamine 2,3-dioxygenase (IDO1) in human epithelial cells, the permissive cells for the obligate intracellular bacterium Chlamydia trachomatis. IDO1 depletes tryptophan by catabolizing it to kynurenine with consequences for C. trachomatis, which is a tryptophan auxotroph. In vitro studies reveal that tryptophan depletion can result in the formation of persistent (viable but noncultivable) chlamydial forms. Here, we tested the effects of the IDO1 inhibitor, levo-1-methyl-tryptophan (L-1MT), on IFN-γ-induced C. trachomatis persistence. We found that addition of 0.2 mM L-1MT to IFN-γ-exposed infected HeLa cell cultures restricted IDO1 activity at the mid-stage (20 h postinfection [hpi]) of the chlamydial developmental cycle. This delayed tryptophan depletion until the late stage (38 hpi) of the cycle. Parallel morphological and gene expression studies indicated a consequence of the delay was a block in the induction of C. trachomatis persistence by IFN-γ. Furthermore, L-1MT addition allowed C. trachomatis to undergo secondary differentiation, albeit with limited productive multiplication of the bacterium. IFN-γ-induced persistent infections in epithelial cells have been previously reported to be more resistant to doxycycline than normal productive infections in vitro. Pertinent to this observation, we found that L-1MT significantly improved the efficacy of doxycycline in clearing persistent C. trachomatis forms. It has been postulated that persistent forms of C. trachomatis may contribute to chronic chlamydial disease. Our findings suggest that IDO1 inhibitors such as L-1MT might provide a novel means to investigate, and potentially target, persistent chlamydial forms, particularly in conjunction with conventional therapeutics.

Localization of Chlamydia trachomatis hypothetical protein CT311 in host cell cytoplasm

The chlamydia-specific hypothetical protein CT311 was detected both inside and outside of the chlamydial inclusions in Chlamydia trachomatis-infected cells. The extra-inclusion CT311 molecules were distributed in the host cell cytoplasm with a pattern similar to that of CPAF, a known Chlamydia-secreted protease. The detection of CT311 was specific since the anti-CT311 antibody labeling was only removed by absorption with CT311 but not CPAF fusion proteins. In addition, both anti-CT311 and anti-CPAF antibodies only detected their corresponding endogenous proteins without cross-reacting with each other or any other antigens in the whole cell lysates of C. trachomatis-infected cells. Although both CT311 and CPAF proteins were first detected 12 h after infection, localization of CT311 into host cell cytosol was delayed until 24 h while CPAF secretion into host cell cytosol was already obvious by 18 h after infection. The host cell cytosolic localization of CT311 was further confirmed in human primary cells. CT311 was predicted to contain an N-terminal secretion signal sequence and the CT311 signal sequence directed secretion of PhoA into bacterial periplasmic region in a heterologous assay system, suggesting that a sec-dependent pathway may play a role in the secretion of CT311 into host cell cytosol. This hypothesis is further supported by the observation that secretion of CT311 in Chlamydia-infected cells was blocked by a C16 compound known to inhibit signal peptidase I. These findings have provided important molecular information for further understanding the C. trachomatis pathogenic mechanisms.

Chlamydophila pneumoniae attachment and infection in low proteoglycan expressing human lymphoid Jurkat cells

This study investigated the proteoglycan (PG)-dependent mechanism of Chlamydophila pneumoniae attachment to lymphocytic cells. Lymphoid Jurkat cells and epithelial HEp-2 cells were statically infected with C. pneumoniae (TW183). Transmission electron microscopy and assessment of inclusion-forming units indicated that the bacteria grew normally in Jurkat cells and were capable of producing secondary infection; however, they grew at a slower rate than in HEp-2 cells. RT-PCR analysis indicated that HEp-2 cells strongly expressed PG-core protein encoding genes, thereby sustaining glycosaminoglycans (GAGs), such as heparin, on the cellular surface. Similar gene expression levels were not observed in Jurkat cells, with the exception of glypican-1. Immunofluorescence analysis also supported strong heparin expression in HEp-2 cells and minimal expression in Jurkat cells, although heparan sulfate pretreatment significantly inhibited bacterial attachment to both cell types. Immunofluorescent co-staining with antibodies against chlamydial LPS and heparin did not identify bacterial and heparin co-localization on Jurkat cells. We also confirmed that when C. pneumoniae was statically infected to human CD4(+) peripheral blood lymphocytes known not expressing detectable level of heparin, the bacteria attached to and formed inclusion bodies in the cells. Thus, the attachment mechanism of C. pneumoniae to Jurkat cells with low PG expression is unique when compared with HEp-2 cells and potentially independent of GAGs such as heparin.

Permissivity of Vero cells, human pneumocytes and human endometrial cells to Waddlia chondrophila

Growing evidence suggests that the bacterium Waddlia chondrophila, a novel member of the Chlamydiales order, is an agent of miscarriage in humans and abortion in ruminants. We thus investigated the permissivity of three epithelial cell lines, primate Vero kidney cells, human A549 pneumocytes and human Ishikawa endometrial cells to this strict intracellular bacteria. Bacterial growth kinetics in these cell lines was assessed by quantitative PCR and immunofluorescence and our results demonstrated that W. chondrophila enters and efficiently multiplies in these epithelial cell lines. Additionally, confocal and electron microscopy indicated that the bacteria co-localize with host cell mitochondria. Within Vero and A549 cells, intracellular growth of W. chondrophila was associated with a significant decrease in host cell viability while no such cytophatic effect was detected in Ishikawa cells. Bacterial cell growth in this endometrial cell line stopped 48 h after infection. This stop in the replication of W. chondrophila coincided with the appearance of large aberrant bodies, a form of the bacteria also observed in Chlamydiaceae and associated with persistence. This persistent state of W. chondrophila may explain recurrent episodes of miscarriage in vivo, since the bacteria might reactivate within endometrial cells following hormonal changes that occur during pregnancy.

Chlamydia pneumoniae infection and Alzheimer's disease: a connection to remember?

Alzheimer's disease (AD) is the most common cause of dementia in the elderly, whereby it is customary to distinguish between early familial FAD and late-onset AD (LOAD). The development of LOAD, the most prevalent form of AD, is believed to be a multifactorial process that may also involve infections with bacterial or viral pathogens. After the first report on the presence of Chlamydia pneumoniae (Cpn) in brains of patients with AD appeared in 1998, this bacterium has most often been implicated in AD pathogenesis. However, while some studies demonstrate a clear association between Cpn infection and AD, others have failed to confirm these findings. This might be due to heterogeneity of the specimens analyzed and lack of standardized detection methods. Additionally, non-availability of suitable chlamydial infection models severely hampers research in the field. In this review, we will critically discuss the possible role of Cpn in the pathogenesis of LOAD in light of the available data. We will also present three mutually non-exclusive hypotheses how Cpn might contribute to the pathogenesis of AD.

Stability of Chlamydophila pneumoniae in a harsh environment without a requirement for acanthamoebae

The effect of actual interactions between Chlamydophila pneumoniae and amoebae (Acanthamoeba) on the survival of C. pneumoniae was investigated. C. pneumoniae and amoebae were detected in 75 soil samples by IFU assay and PCR. Although C. pneumoniae could not be cultured, the DNA prevalence of C. pneumoniae and amoebae in natural soil was 20% and 92% (no correlation between the prevalence of DNA was observed). The viability of C. pneumoniae spiked in autoclaved soil was assessed by IFU assay and RT-PCR. Although the number of infective progeny decreased for three days, transcripts of C. pneumoniae were detected for up to 98 days independently of amoebae. The stability of C. pneumoniae in liquid medium was also assessed by IFU assay and transmission electron microscopy. The bacteria could survive at 15 degrees C for 14 days independently of amoebae. Bacteria cultured without amoebae were confirmed to have normal structures. Thus, the presence of amoebae has no effect on C. pneumoniae survival, and the bacteria can survive in the absence of host cells for an extended period of time.

Novel Parachlamydia acanthamoebae quantification method based on coculture with amoebae

Parachlamydia acanthamoebae, belonging to the order Chlamydiales, is an obligately intracellular bacterium that infects free-living amoebae and is a potential human pathogen. However, no method exists to accurately quantify viable bacterial numbers. We present a novel quantification method for P. acanthamoebae based on coculture with amoebae. P. acanthamoebae was cultured either with Acanthamoeba spp. or with mammalian epithelial HEp-2 or Vero cells. The infection rate of P. acanthamoebae (amoeba-infectious dose [AID]) was determined by DAPI (4',6-diamidino-2-phenylindole) staining and was confirmed by fluorescent in situ hybridization. AIDs were plotted as logistic sigmoid dilution curves, and P. acanthamoebae numbers, defined as amoeba-infectious units (AIU), were calculated. During culture, amoeba numbers and viabilities did not change, and amoebae did not change from trophozoites to cysts. Eight amoeba strains showed similar levels of P. acanthamoebae growth, and bacterial numbers reached ca. 1,000-fold (10(9) AIU preculture) after 4 days. In contrast, no increase was observed for P. acanthamoebae in either mammalian cell line. However, aberrant structures in epithelial cells, implying possible persistent infection, were seen by transmission electron microscopy. Thus, our method could monitor numbers of P. acanthamoebae bacteria in host cells and may be useful for understanding chlamydiae present in the natural environment as human pathogens.

Chlamydial CT441 is a PDZ domain-containing tail-specific protease that interferes with the NF-kappaB pathway of immune response

Chlamydia species are bacterial pathogens that affect over 140 million individuals worldwide. Ocular infection by Chlamydia trachomatis is the leading cause of preventable blindness, and urogenital tract infection by Chlamydia causes sexually transmitted disease. As obligate intracellular organisms, Chlamydia species have evolved mechanisms to evade the host immune system, including the degradation of the transcription factors regulatory factor X5 and upstream stimulation factor 1, which are required for the expression of major histocompatibility complex molecules I and II by CPAF and cleavage of p65 of the NF-kappaB pathway by the encoded CT441 protein. Here, we report the characterization of CT441 as a tail-specific protease. CT441 contains a PDZ domain of protein-protein interactions and a Ser/Lys dyad catalytic unit. Mutation at either Ser455 or Lys481 in the active site ablated CT441 activity of p65 cleavage. In addition, we found that the production of CT441 Tsp, which was detected at the middle and late stages of an infection, correlated with p65 cleavage activity. In addition to high homology, human and mouse p65 proteins also contain an identical C-terminal tail of 22 amino acid (aa) residues. However, only human p65 was susceptible to cleavage. Using molecular biology approaches, we mapped the p65 cleavage site(s) to a region that differs from that of mouse p65 by 6 aa residues. Additionally, the substitution of T352 with a proline inhibited p65 cleavage. Together, the study demonstrates that CT441 is a tail-specific protease that is capable of interfering with the NF-kappaB pathway of host antimicrobial and inflammatory responses.

Chlamydia trachomatis type III secretion: evidence for a functional apparatus during early-cycle development

The obligate intracellular bacterium Chlamydia trachomatis occupies a parasitophorous vacuole termed an inclusion. During its intracellular developmental cycle, C. trachomatis maintains this intracellular niche, presumably by expressing a type III secretion system, which deploys a set of host cell-interactive proteins including inclusion membrane-localized proteins termed Incs. Some Incs are expressed and secreted by 2 h (early cycle) after infection, whereas the expression of type III-specific genes is not detectable until 6-12 h (mid-cycle). To resolve this paradox, we investigated the presence of a type III apparatus on elementary bodies (EBs) that might function early in infection. We demonstrate the existence of the type III secretory apparatus by matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) and immunoblot analyses of purified EB extracts. Immunoblots using polyclonal antibodies specific for the core apparatus component CdsJ identified this protein in both EB and reticulate body (RB) extracts. Furthermore, CdsJ-specific signals were detected by immunoblot of whole infected-culture extracts and by indirect immunofluorescence of infected monolayers at times before the detection of cdsJ-specific message. Finally, expression of IncC, expressed by 2 h after infection during C. trachomatis infections, in Yersinia pseudotuberculosis resulted in its secretion via the Yersinia type III apparatus. Based on these data, we propose a model in which type III secretion pores are present on EBs and mediate secretion of early Incs and possible additional effectors. Mid-cycle expression of type III genes would then replenish secretion apparatus on vegetative RBs and serve as a source of secretion pores for subsequently formed EBs.

Evidence for the secretion of Chlamydia trachomatis CopN by a type III secretion mechanism

The medically significant, obligate intracellular pathogen Chlamydia trachomatis replicates within vacuoles termed inclusions. A developmental cycle is initiated after entry into a host cell and is manifested by the transformation of infectious elementary bodies (EBs) to larger, non-infectious reticulate bodies (RBs). Analysis of the C. trachomatis genome has revealed that chlamydiae possess genes that may encode a type III secretion apparatus. In other Gram-negative pathogens, the type III secretion mechanism is used to target virulence factors directly to the host cell cytoplasm and is essential for full virulence. To evaluate the possibility of a functional type III secretion mechanism in C. trachomatis, we initially focused on a locus containing genes encoding products with similarity to chaperones (Scc1), secretion pore components (Cds1 and Cds2) and secreted proteins (CopN) from other type III systems. Gene expression was tested by reverse transcriptase-polymerase chain reaction (RT-PCR) of total RNA extracted from infected HeLa cell monolayers at 2, 6, 12 and 20 h after infection and normalized for the number of C. trachomatis genomes present. Message was detected for Scc1 at all times, whereas message for all other tested genes was detected in significant amounts at 12 h and 20 h. Immunoblot analysis with Scc1- and CopN-specific antibodies revealed that CopN and Scc1 were present in EBs, RBs and whole-culture extracts harvested 20 h after infection. CopN is homologous to the secreted protein YopN of Yersinia sp., and analysis of monolayers 20 h after infection via indirect immunofluorescence showed specific labelling of inclusion membranes when probed with CopN-specific antibodies but not with Scc1-specific antibodies. His-tagged CopN and a chlamydial cytoplasmic control protein (NrdB) were expressed in Yersinia enterocolitica containing or lacking the virulence plasmid pYV. CopN, but not NrdB, was secreted by Y. enterocolitica in a Ca2+- and pYV-dependent fashion. These data indicate that components of the putative type III apparatus of C. trachomatis are expressed and that at least one of these products is secreted by chlamydiae to the inclusion membrane. The observation that CopN is also secreted by the Yersinia type III apparatus provides support for the notion that chlamydiae secrete proteins via a type III mechanism.

Chlamydial envelope components and pathogen-host cell interactions

Few bacterial pathogens are as widespread in nature or as capable of eliciting such a diversity of disease syndromes as are the chlamydiae. As obligate intracellular organisms, they pose a special research challenge in defining the molecular components and mechanisms for productive growth within host cells and the overall progress of infection throughout host tissue. Although a comprehensive view of chlamydial envelope composition and respective functions in pathogenesis is far from complete, ongoing investigations continue to expose new and intriguing avenues for exploration.

Monoclonal antibodies define genus-specific, species-specific, and cross-reactive epitopes of the chlamydial 60-kilodalton heat shock protein (hsp60): specific immunodetection and purification of chlamydial hsp60

Ocular and urogenital tract infections with Chlamydia trachomatis can progress to chronic inflammatory diseases that produce blindness and tubal infertility. The pathophysiology of these chronic disease conditions is thought to be immunologically mediated, and the chlamydial 60-kDa heat shock protein (hsp60) has been implicated as a major target antigen that stimulates the immunopathological response. The lack of chlamydial hsp60 antibodies and purified hsp60 has severely restricted studies to define more thoroughly the role of this protein in the immunopathogenesis of chlamydial disease. We produced a panel of antichlamydial hsp60 monoclonal antibodies (MAbs) and defined their specificities by immunoblotting against lysates of C. trachomatis, C. psittaci, and six other genera of bacteria. Three patterns of anti-hsp60 immunoreactivity were observed: chlamydial species specific, chlamydial genus specific, and cross-reactive. The epitopes recognized by these MAbs were localized within the primary amino acid sequence of hsp60 by immunoblotting against recombinant amino-terminal truncated hsp60 fusion polypeptides and then precisely mapped by use of overlapping synthetic peptides. The majority of the MAbs mapped to either the amino or the carboxyl termini of hsp60. Epitopes defining all three MAb reactivities mapped within amino-terminal residues 6 to 16. Genus-specific hsp60 MAbs mapped to epitopes located within this region and to residues 17 to 28 and 177 to 189. Antichlamydial hsp60 MAbs stained inclusions as effectively as MAbs specific for the major outer membrane protein. Homogeneous preparations of full-length recombinant chlamydial hsp60 and amino-terminal truncated recombinant hsp60 polypeptides were obtained by immunoabsorption chromatography with an hsp60 MAb reactive to the carboxyl terminus of the protein. Thus, the antichlamydial MAbs described here should be extremely useful for the specific immunodetection of hsp60 in tissues from individuals having different disease manifestations and for the purification of hsp60 or truncated hsp60 polypeptides for use in serologic and lymphocyte proliferation assays. The availability of these MAbs will facilitate studies to define more precisely the role of hsp60 in the immunopathogenesis of chlamydial disease.

Chlamydia parasitism: ultrastructural characterization of the interaction between the chlamydial cell envelope and the host cell

Ultrastructural analysis of the growth cycles of Chlamydia trachomatis and Chlamydia psittaci showed that the chlamydial cell envelope became rigid and septated at the time of the reorganization from reticulate to elementary body. This process occurred in the immediacy of the inclusion membrane and in close proximity with the mitochondria or the endoplasmic reticulum of the host cell.

Recent advances in Chlamydia trachomatis

Chlamydia trachomatis is an obligate intracellular energy parasitic bacterium with a genome of 660 X 10(6) daltons, possessing a plasmid and unique life cycle which includes the differentiation of the infective elementary body to a replicative reticulate body. C. trachomatis is the etiological agent of trachoma, which affects approximately 500 million people in developing countries. Recently it became evident that in industrialised Western nations certain strains of C. trachomatis are the most common cause of sexually transmitted infections such as non-gonococcal urethritis, cervicitis, endometritis, salpingitis and subsequent ectopic pregnancies or infertility, perihepatitis, neonatal conjunctivitis and pneumonia, adult conjunctivitis and epididymitis. Since C. trachomatis infections are often asymptomatic, widespread screening of sexually active young people is needed in order to initiate early antibiotic treatment which may prevent serious complications such as ectopic pregnancies and infertility. Development of sensitive and simple techniques for mass screening for detection of Chlamydia in excretions as well as techniques for detection of specific markers of chronic internal infections (such as Chlamydia specific IgA antibodies) is of great importance.

Disulfide-mediated interactions of the chlamydial major outer membrane protein: role in the differentiation of chlamydiae?

The effects of exogenous reducing agents on a number of biological properties of purified Chlamydia trachomatis LGV-434 and Chlamydia psittaci meningopneumonitis elementary bodies (EBs) have been examined in an attempt to identify in vitro correlates of early events in the differentiation of the infectious EB to the replicative cell type, the reticulate body (RB). Treatment of EBs with dithiothreitol elicited a number of changes normally associated with differentiation to the RB. EBs in the presence of 10 mM dithiothreitol displayed enhanced rates of [14C]glutamate oxidation, reduced infectivity, and decreased osmotic stability, and their Machiavello staining properties changed to those characteristic of the RB. A true differentiation of EB to RB did not take place under these conditions, since EBs treated in this manner and examined by transmission electron microscopy did not demonstrate increased size or decreased electron density as do isolated RBs. Additional studies were initiated to identify the macromolecules involved in this process. With polyacrylamide gel electrophoresis and immunoblotting procedures with monoclonal and polyclonal monospecific antibodies, the chlamydial major outer membrane protein was found to be the predominant component that varied under reducing versus nonreducing conditions. Furthermore, the extent of disulfide-mediated cross-linking of the major outer membrane protein varied between the infective and replicative forms of the C. trachomatis LGV-434 life cycle. Implications of disulfide interactions in the life cycle of chlamydiae are discussed.

Structural and polypeptide differences between envelopes of infective and reproductive life cycle forms of Chlamydia spp

Significant differences in cysteine-containing proteins and detergent-related solubility properties were observed between outer membrane protein complexes of reproductive (reticulate body) and infective (elementary body) forms of Chlamydia psittaci (6BC). Elementary bodies harvested at 48 h postinfection possessed a 40-kilodalton major outer membrane protein and three extraordinarily cysteine-rich outer membrane proteins of 62, 59, and 12 kilodaltons, all of which were not solubilized by sodium dodecyl sulfate in the absence of thiol reagents. Intracellularly dividing reticulate bodies harvested at 21 h postinfection were severely deficient in the cysteine-rich proteins but possessed almost as much major outer membrane protein as did the elementary bodies. Most of the major outer membrane protein of reticulate bodies was solubilized by sodium dodecyl sulfate and was present in envelopes as monomers, although a proportion formed disulfide-cross-linked oligomers. By 21 to 24 h postinfection, reticulate bodies commenced synthesis of the cysteine-rich proteins which were found in outer membranes as disulfide-cross-linked complexes. The outer membranes of reticulate bodies of Chlamydia trachomatis (LGV434) also were found to be deficient in cysteine-rich proteins and to be more susceptible to dissociation in sodium dodecyl sulfate than were outer membranes of elementary bodies.

The genus-specific antigen of Chlamydia: resemblance to the lipopolysaccharide of enteric bacteria

A strong immunological cross-reaction between a major glycolipid antigen of Chlamydia and the innermost (Re) core of the lipopolysaccharide of enteric bacteria was demonstrated with the aid of mutants in which the Re structure is exposed. The chlamydial glycolipid resembled the Re lipopolysaccharide in molecular size, solubility, and endotoxic properties and may thus be functionally equivalent to lipopolysaccharide, an essential and characteristic component of the outer membrane of Gram-negative bacteria.

Chlamydia trachomatis has penicillin-binding proteins but not detectable muramic acid

Chlamydia trachomatis LGV-434 was grown in HeLa 229 cells. Benzylpenicillin completely inhibited the formation of infectious elementary bodies (EBs) at a concentration of 19 pmol/ml or higher and produced abnormally large reticulate bodies (RBs) in the inclusions at 30 pmol/ml or higher. The possible targets for penicillin in C. trachomatis were three penicillin-binding proteins (PBPs) which were identified in the Sarkosyl-soluble fractions of both RBs and EBs. The apparent subunit molecular weights were 88,000 (PBP 1), 61,000 (BPB 2), and 36,000 (PBP 3). The 50% binding concentrations of [3H]penicillin for PBPs 1 to 3 in EBs and RBs were between 7 and 70 pmol/ml. Such high susceptibility to penicillin was shown by an organism that did not have detectable muramic acid (less than 0.02% by weight) in preparations of either whole cells or sodium dodecyl sulfate-insoluble residues.

Modulation of the host immune response as a result of Chlamydia psittaci infection

After intraperitoneal injection of mice with infectious, inactivated, or envelope preparations of the elementary body of Chlamydia psittaci, lymphocyte transformation of spleen cells to the mitogens concanavalin A, phytohemagglutinin, and lipopolysaccharide was significantly reduced 1 and 2 weeks postinjection. Lymphocyte response returned to the control values by 4 weeks. Similarly, transformation of cells by chlamydial antigen was not detected until 4 weeks postinjection. Injection of the noninfectious intracellular reticulate body, in contrast, had little effect on transformation of cells to concanavalin A. When control spleen cells were incubated with infectious or inactivated elementary bodies in vitro, response to all three mitogens was also reduced. The sooner the organisms were added after the addition of mitogen, the greater the reduction in transformation. Incubation with elementary body envelopes and reticulate bodies had no effect on lymphocyte transformation of the spleen cells to concanavalin A. The relationship between the observed ability to reduce the response in the in vitro assay of lymphocyte transformation and the actual in vivo establishment of infection is discussed.

Identification of a major envelope protein in Chlamydia spp

A major cell envelope protein of Chlamydia psittaci with a molecular weight of approximately 43,000 was identified and partially characterized. It was present at all stages of the C. psittaci developmental cycle. A major protein with a similar molecular weight was also observed in two Chlamydia trachomatis strains.

Isolation and electron microscopic observations of intracytoplasmic inclusions containing Chlamydia psittaci

Intracytoplasmic inclusions containing Chlamydia psittaci were isolated by a newly established method. Infected L-cells at 20 h after infection were suspended in 0.25 M sucrose-tris(hydroxymethyl)aminomethane buffer containing ethylene-diaminetetraacetic acid, homogenized in a Dounce tissue grinder, and filtered through a 2,000-mesh screen. Isolated inclusions were stabilized in 5% bovine serum albumin in 10 mM tris(hydroxymethyl)aminomethane buffer. Electron microscopic observations revealed the presence of surface projections on the vegetative, reticulate bodies and a direct connection between the reticulate bodies and the inclusion membrane by means of projections.

Modifications of the envelope of Chlamydia psittaci during its developmental cycle: freeze-fracture study of complementary replicas

Examination of complementary replicas obtained by freeze-fracture of Chlamydia psittaci revealed, at the level of the plasma membrane, a progressive differentiation of "crate-like formations," which likely correspond to transmembranal pores. Recognition of "early" and "late" stages observed in the intermediate bodies permitted detailed study of the developmental cycle of this chlamydia.

The chlamydia: molecular biology of procaryotic obligate parasites of eucaryocytes

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Protein-carbohydrate-lipid complex isolated from the cell envelopes of Chlamydia psittaci in alkaline buffer and ethylenediaminetetraacetate

Exposure of isolated cell envelopes from purified infectious elementary (EB) of Chlamydia psittaci to sodium carbonate-bicarbonate buffer at pH 10 plus ethylenediaminetetraacetate (EDTA) results in partial solubilization of the total protein. The released materials represent 20% of the dry weight, 16% of the total protein, 40% of the total carbohydrate, and 9% of the total lipid of the cell envelopes. Sucrose density gradient centrifugation, and Sephadex G-200, Sepharose 4B, or diethylaminoethyl-cellulose column chromatography, reveal a protein-carbohydrate-lipid complex of several hundred thousand molecular weight that contains 50% protein. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the isolated EB cell envelopes reveals two major protein bands, A and B, with estimated molecular masses of approximately 85,000 and 53,000, respectively, both of which also stain for the presence of carbohydrate and lipid. Gel electrophoresis of the protein-carbohydrate-lipid complex reveals two protein bands, C and D, with estimated molecular weights of approximately 17,000 and 13,000, respectively, which contain lipid and a small amount of carbohydrate; bands A and B are not present in the complex. Gel electrophoresis of the cell envelope residues after extraction of the complex with alkali and EDTA shows a single main band, corresponding to the position of band B, which contains protein, carbohydrate, and lipid; band A is completely missing. B and A is believed to be a component of the complex, which is split into two subunits on alkali solubilization.

Effect of alkali on the structure of cell envelopes of Chlamydia psittaci elementary bodies

Suspensions of isolated cell envelopes of infectious elementary bodies (EB) of Chlamydia psittaci at alkaline pH showed a rapid, extensive decrease in absorbance, accompanied by the release of a cell envelope component in a sedimentable form. This phenomenon was observed both at 0 C and with envelopes which had been previously heated to 100 C. Monovalent and divalent cations effectively inhibited the turbidity loss, whereas ethylenediaminetetraacetate (EDTA) caused an accelerated decrease in turbidity. The turbidity loss observed after incubation of the envelopes at alkaline pH could be reversed to the level of the initial value by dialysis against distilled water containing Mg2+. Thin-section electron photomicrographs of purified EB exposed to alkaline buffer with EDTA revealed the loss of the internal contents of cells, but these cells still maintained their round shapes. The cell surface of treated EB appeared pitted in negatively stained preparations, whereas intact EB had a smooth surface. Electron microscopic studies on negatively stained preparations of the clear supernatant obtained after the treatment of the envelope with alkaline buffer containing EDTA demonstrated the presence of spherical particles, approximately 6 to 7 nm in diameter, and rodlike particles, which appeared to be made up of two or more spherical particles.

Proteinase produced by Chlamydia psittaci in L cells

L cells (mouse fibroblasts) infected with Chlamydia psittaci (strain meningopneumonitis) produced a proteinase differing in solubility in ammonium sulfate from the proteinase of uninfected L cells. Synthesis of the enzyme was inhibited by chloramphenicol but not by cycloheximide, indicating that the new proteinase in infected L cells was synthesized by Chlamydia psittaci. The chlamydial proteinase had no demonstrable ion requirements and was not inhibited by a variety of inhibitors of proteinase activity. Gel filtration experiments suggested a molecular weight of approximately 250,000. The proteinase appeared in infected L cells at the time host cells began to die and the large chlamydial cells began to reorganize into small ones. Some possible functions for the chlamydial proteinase were proposed.

Separation of the polypeptides of Chlamydia and its cell walls by polyacrylamide gel electrophoresis

The polypeptide composition of Chlamydia was examined by acrylamide gel electrophoresis. When the polypeptide patterns of purified infectious elementary bodies (EB) of C. psittaci meningopneumonitis strain, 6BC strain, and C. trachomatis T'ang strain were compared, no significant differences were observed. The polypeptide patterns of whole EB and reticulate bodies (RB) appeared to overlap, but differences were found. In EB cell walls, nine main and several minor bands of polypeptides were observed in gels containing sodium lauryl sulfate, and the eighth main band from the top of the gel stained positive with periodic acid-Schiff reagent. On the other hand, the polypeptides in bands 3, 6, and 8 in EB cell walls were missing or minor in RB cell walls, and the ninth band was clearly stained by PAS. Band 8 was also stained slightly. Purified subunits, which occur as a lattice structure on the inside layer of EB cell walls but are largely missing in RB cell walls, contained bands 4, 6, and 8, and band 8 was PAS positive. These results indicate that significant polypeptide synthesis or reorganization in the cell walls occurs during the growth cycle.

Fine structures of cell envelopes of Chlamydia organisms as revealed by freeze-etching and negative staining techniques

The cell walls of Chlamydia psittaci (meningopneumonitis strain) were examined by the freeze-etching and negative staining techniques. It was observed that the cleaved convex surface of the developmental, reticulate body was covered with numerous non-etchable particles 9 to 10 nm in diameter, these particles being rarely seen on the concave surface. Similarly, the convex surface of the mature, elementary body (EB) was covered with many particles but the concavity lacked these particles. After etching, the smooth concave surface of the EB appeared to have a hexagonally arrayed subunit structure, on which the button structure (B structure) was observed. Each B structure had a diameter of 27 nm and several B structures were grouped together in a hexagonal arrangement with a center-to-center spacing of 45 nm. In a limited area of the negatively stained EB cell wall, hexagonally arrayed rosette structures were present, with a center-to-center spacing similar to the B structures seen in the freeze-etched preparation. Each rosette, about 19 to 20 nm in diameter, appeared to be composed of a radial arrangement of nine subunits. The freeze-fractured cell wall-cytoplasmic membrane complexes indicated that the outer surface of the cytoplasmic membrane which appeared as the convex surface was covered with the fine particles, and thus it was likely that frozen EB was cleaved at the gap between the cell wall and ctyoplasmic membrane. On the cleaved inclusion, several groups of fine particles were observed. In each group, the particles were arranged hexagonally with the spacing ranging from 20 to 50 nm.

Electron microscope observations on the effects of polymixin B sulfate on cell walls of Chlamydia psittaci

The effects of polymixin B sulfate on cell walls of mature elementary body (EB) and of immature developmental reticulate body (RB) of Chlamydia psittaci were investigated. When purified EB were treated with polymixin (10(4) units per ml or more) at 37 C for 60 min, about 70% of EB was found to be covered with a number of projections. Further incubation did not increase the percentage affected. The infectivity after treatment as assayed by the inclusion counting technique was reduced by 70% of the original titer. These results suggest that EB with the projections are no longer infective. The projections had obscure outlines and were 20 to 40 nm in diameter when seen in thin sections. In the negatively stained preparations, the projections were composed of aggregations of fine particles 4 to 5 nm in diameter. Treatment with sodium dodecyl sulfate at the same concentration used for cell wall isolation removed the projections completely, and the cell walls were converted to rather ragged forms apparently composed of outside and inside layers. When RB cell walls prepared from infected cells at 18 hr after infection were treated with polymixin at the same concentration, the projections having the same morphology with those seen on treated EB cell walls were observed only on the inside surface of cell wall.