Structural study on a lipopolysaccharide from Coxiella burnetii strain Nine Mile in avirulent phase II

Additive-assisted synthesis of α-Kdo glycosides with peracetylated glycosyl ynenoate as a donor

A DMF-modulated glycosylation approach for the stereoselective synthesis of α-Kdo glycosides with readily accessible peracetylated Kdo ynenoate as a donor was described. By utilizing this approach, we completed the synthesis of various linkage types of Kdo-Kdo disaccharides and the α-Kdo-containing protected trisaccharide variant relevant to the lipopolysaccharide of Coxiella burnetii strain Nine Mile.

Identification and Characterization of an HtrA Sheddase Produced by Coxiella burnetii

Having previously shown that soluble E-cadherin (sE-cad) is found in sera of Q fever patients and that infection of BeWo cells by C. burnetii leads to modulation of the E-cad/β-cat pathway, our purpose was to identify which sheddase(s) might catalyze the cleavage of E-cad. Here, we searched for a direct mechanism of cleavage initiated by the bacterium itself, assuming the possible synthesis of a sheddase encoded in the genome of C. burnetii or an indirect mechanism based on the activation of a human sheddase. Using a straightforward bioinformatics approach to scan the complete genomes of four laboratory strains of C. burnetii, we demonstrate that C. burnetii encodes a 451 amino acid sheddase (CbHtrA) belonging to the HtrA family that is differently expressed according to the bacterial virulence. An artificial CbHtrA gene (CoxbHtrA) was expressed, and the CoxbHtrA recombinant protein was found to have sheddase activity. We also found evidence that the C. burnetii infection triggers an over-induction of the human HuHtrA gene expression. Finally, we demonstrate that cleavage of E-cad by CoxbHtrA on macrophages-THP-1 cells leads to an M2 polarization of the target cells and the induction of their secretion of IL-10, which "disarms" the target cells and improves C. burnetii replication. Taken together, these results demonstrate that the genome of C. burnetii encodes a functional HtrA sheddase and establishes a link between the HtrA sheddase-induced cleavage of E-cad, the M2 polarization of the target cells and their secretion of IL-10, and the intracellular replication of C. burnetii.

Modulation of the E-cadherin in human cells infected in vitro with Coxiella burnetii

High concentration of soluble E-cadherin (E-cad) was previously found in sera from Q fever patients. Here, BeWo cells which express a high concentration of E-cad were used as an in vitro model to investigate the expression and function of E-cad in response to infection by Coxiella burnetii, the etiological agent of Q fever. Infection of BeWo cells with C. burnetii leads to a decrease in the number of BeWo cells expressing E-cad at their membrane. A shedding of soluble E-cad was associated with the post-infection decrease of membrane-bound E-cad. The modulation of E-cad expression requires bacterial viability and was not found with heat-inactivated C. burnetii. Moreover, the intracytoplasmic cell concentration of β-catenin (β-cat), a ligand of E-cad, was reduced after bacterial infection, suggesting that the bacterium induces modulation of the E-cad/β-cat signaling pathway and CDH1 and CTNNB1 genes transcription. Finally, several genes operating the canonical Wnt-Frizzled/β-cat pathway were overexpressed in cells infected with C. burnetii. This was particularly evident with the highly virulent strain of C. burnetii, Guiana. Our data demonstrate that infection of BeWo cells by live C. burnetii modulates the E-cad/β-cat signaling pathway.

Natural Exposure- and Vaccination-Induced Profiles of Ex Vivo Whole Blood Cytokine Responses to Coxiella burnetii

Q fever is a zoonotic disease caused by the highly infectious Gram-negative coccobacillus, Coxiella burnetii (C. burnetii). The Q fever vaccine Q-VAX® is characterised by high reactogenicity, requiring individuals to be pre-screened for prior exposure before vaccination. To date it remains unclear whether vaccine side effects in pre-exposed individuals are associated with pre-existing adaptive immune responses to C. burnetii or are also a function of innate responses to Q-VAX®. In the current study, we measured innate and adaptive cytokine responses to C. burnetii and compared these among individuals with different pre-exposure status. Three groups were included: n=98 Dutch blood bank donors with unknown exposure status, n=95 Dutch village inhabitants with known natural exposure status to C. burnetii during the Dutch Q fever outbreak of 2007-2010, and n=96 Australian students receiving Q-VAX® vaccination in 2021. Whole blood cytokine responses following ex vivo stimulation with heat-killed C. burnetii were assessed for IFNγ, IL-2, IL-6, IL-10, TNFα, IL-1β, IP-10, MIP-1α and IL-8. Serological data were collected for all three cohorts, as well as data on skin test and self-reported vaccine side effects and clinical symptoms during past infection. IFNγ, IP-10 and IL-2 responses were strongly elevated in individuals with prior C. burnetii antigen exposure, whether through infection or vaccination, while IL-1β, IL-6 and TNFα responses were slightly increased in naturally exposed individuals only. High dimensional analysis of the cytokine data identified four clusters of individuals with distinct cytokine response signatures. The cluster with the highest levels of adaptive cytokines and antibodies comprised solely individuals with prior exposure to C. burnetii, while another cluster was characterized by high innate cytokine production and an absence of C. burnetii-induced IP-10 production paired with high baseline IP-10 levels. Prior exposure status was partially associated with these signatures, but could not be clearly assigned to a single cytokine response signature. Overall, Q-VAX® vaccination and natural C. burnetii infection were associated with comparable cytokine response signatures, largely driven by adaptive cytokine responses. Neither individual innate and adaptive cytokine responses nor response signatures were associated retrospectively with clinical symptoms during infection or prospectively with side effects post-vaccination.

Soluble antigens derived from Coxiella burnetii elicit protective immunity in three animal models without inducing hypersensitivity

Q fever is caused by the intracellular bacterium Coxiella burnetii, for which there is no approved vaccine in the United States. A formalin-inactivated whole-cell vaccine (WCV) from virulent C. burnetii NMI provides single-dose long-lived protection, but concerns remain over vaccine reactogenicity. We therefore sought an alternate approach by purifying native C. burnetii antigens from the clonally derived avirulent NMII strain. A soluble bacterial extract, termed Sol II, elicits high-titer, high-avidity antibodies and induces a CD4 T cell response that confers protection in naive mice. In addition, Sol II protects against pulmonary C. burnetii challenge in three animal models without inducing hypersensitivity. An NMI-derived extract, Sol I, enhances protection further and outperforms the WCV gold standard. Collectively, these data represent a promising approach to design highly effective, non-reactogenic Q fever vaccines.

Quantitative Proteome Profiling of Coxiella burnetii Reveals Major Metabolic and Stress Differences Under Axenic and Cell Culture Cultivation

Coxiella burnetii is the causative agent of the zoonotic disease Q fever. To date, the lipopolysaccharide (LPS) is the only defined and characterized virulence determinant of C. burnetii. In this study, proteome profiles of C. burnetii Nine Mile phase I (RSA 493, NMI) and its isogenic Nine Mile phase II (RSA 439 NMII) isolate with a deep rough LPS were compared on L-929 mouse fibroblasts and in complex (ACCM-2), and defined (ACCM-D) media. Whole proteome extracts were analyzed using a label-free quantification approach. Between 659 and 1,046 C. burnetii proteins of the 2,132 annotated coding sequences (CDS) were identified in any particular experiment. Proteome profiles clustered according to the cultivation conditions used, indicating different regulation patterns. NMI proteome profiles compared to NMII in ACCM-D indicate transition from an exponential to a stationary phase. The levels of regulatory proteins such as RpoS, CsrA2, UspA1, and UspA2 were increased. Comparison of the oxidative stress response of NMI and NMII indicated that ACCM-2 represents a high oxidative stress environment. Expression of peroxidases, superoxide dismutases, as well as thioredoxins was increased for NMI. In contrast, in ACCM-D, only osmoregulation seems to be necessary. Proteome profiles of NMII do not differ and indicate that both axenic media represent similar oxidative stress environments. Deep rough LPS causes changes of the outer membrane stability and fluidity. This might be one reason for the observed differences. Proteins associated with the T4SS and Sec translocon as well as several effector proteins were detectable under all three conditions. Interestingly, none of these putatively secreted proteins are upregulated in ACCM-2 compared to ACCM-D, and L-929 mouse fibroblasts. Curiously, a higher similarity of proteomic patterns (overlapping up- and downregulated proteins) of ACCM-D and bacteria grown in cell culture was observed. Particularly, the proteins involved in a better adaptation or homeostasis in response to the harsh environment of the parasitophorous vacuole were demonstrated for NMI. This semi-quantitative proteomic analysis of C. burnetii compared axenically grown bacteria to those propagated in cell culture.

Screening for Q fever. A tertiary care hospital-based experience in central Saudi Arabia

OBJECTIVES

To evaluate the presence of Coxiella burnetii  (C. brunetii) infection among patients presenting with fever of unknown origin (FUO).

METHODS

A cross-sectional study of 100 patients (54 men and 46 women; mean age: 34.3 ± 19.2 years) with FUO was conducted at King Khalid University Hospital, Riyadh, Saudi Arabia between March 2015 and June 2016. Phase 1 and phase 2 C. burnetii-specific antibodies in serum samples were detected by enzyme-linked immunosorbent assay.

RESULTS

Coxiella burnetii phase 1 and phase 2 antibodies were detected in 16% of the patients. Phase 2 IgM was present in 2% of the patients, whereas phase 2 IgG antibodies were detected in 11%  of the patients. Coxiella burnetii-specific phase 1 IgG was found in 2% of the patients, and 8% of the patients harbored phase 1 IgA antibodies in their serum.

CONCLUSION

The presence of C. burnetii-specific antibodies in many patients suffering from FUO highlights the importance of Q fever screening among patients presenting with febrile illness.

Genetic mechanisms of Coxiella burnetii lipopolysaccharide phase variation

Coxiella burnetii is an intracellular pathogen that causes human Q fever, a disease that normally presents as a severe flu-like illness. Due to high infectivity and disease severity, the pathogen is considered a risk group 3 organism. Full-length lipopolysaccharide (LPS) is required for full virulence and disease by C. burnetii and is the only virulence factor currently defined by infection of an immunocompetent animal. Transition of virulent phase I bacteria with smooth LPS, to avirulent phase II bacteria with rough LPS, occurs during in vitro passage. Semi-rough intermediate forms are also observed. Here, the genetic basis of LPS phase conversion was investigated to obtain a more complete understanding of C. burnetii pathogenesis. Whole genome sequencing of strains producing intermediate and/or phase II LPS identified several common mutations in predicted LPS biosynthesis genes. After passage in broth culture for 30 weeks, phase I strains from different genomic groups exhibited similar phase transition kinetics and elevation of mutations in LPS biosynthesis genes. Targeted mutagenesis and genetic complementation using a new C. burnetii nutritional selection system based on lysine auxotrophy confirmed that six of the mutated genes were necessary for production of phase I LPS. Disruption of two of these genes in a C. burnetii phase I strain resulted in production of phase II LPS, suggesting inhibition of the encoded enzymes could represent a new therapeutic strategy for treatment of Q fever. Additionally, targeted mutagenesis of genes encoding LPS biosynthesis enzymes can now be used to construct new phase II strains from different genomic groups for use in pathogen-host studies at a risk group 2 level.

Farming, Q fever and public health: agricultural practices and beyond

Since the Neolithic period, humans have domesticated herbivores to have food readily at hand. The cohabitation with animals brought various advantages that drastically changed the human lifestyle but simultaneously led to the emergence of new epidemics. The majority of human pathogens known so far are zoonotic diseases and the development of both agricultural practices and human activities have provided new dynamics for transmission. This article provides a general overview of some factors that influence the epidemic potential of a zoonotic disease, Q fever. As an example of a disease where the interaction between the environment, animal (domestic or wildlife) and human populations determines the likelihood of the epidemic potential, the management of infection due to the Q fever agent, Coxiella burnetii, provides an interesting model for the application of the holistic One Health approach.

Coxiella burnetii Lipopolysaccharide: What Do We Know?

A small gram-negative bacterium, Coxiella burnetii (C. burnetii), is responsible for a zoonosis called Q fever. C. burnetii is an intracellular bacterium that can survive inside microbicidal cells like monocytes and macrophages by hijacking several functions of the immune system. Among several virulence factors, the lipopolysaccharide (LPS) of C. burnetii is one of the major factors involved in this immune hijacking because of its atypical composition and structure. Thus, the aim of this mini-review is to summarize the repressive effects of C. burnetii LPS on the antibacterial immunity of cells.

Permissiveness of bovine epithelial cells from lung, intestine, placenta and udder for infection with Coxiella burnetii

Ruminants are the main source of human infections with the obligate intracellular bacterium Coxiella (C.) burnetii. Infected animals shed high numbers of C. burnetii by milk, feces, and birth products. In goats, shedding by the latter route coincides with C. burnetii replication in epithelial (trophoblast) cells of the placenta, which led us to hypothesize that epithelial cells are generally implicated in replication and shedding of C. burnetii. We therefore aimed at analyzing the interactions of C. burnetii with epithelial cells of the bovine host (1) at the entry site (lung epithelium) which govern host immune responses and (2) in epithelial cells of gut, udder and placenta decisive for the quantity of pathogen excretion. Epithelial cell lines [PS (udder), FKD-R 971 (small intestine), BCEC (maternal placenta), F3 (fetal placenta), BEL-26 (lung)] were inoculated with C. burnetii strains Nine Mile I (NMI) and NMII at different cultivation conditions. The cell lines exhibited different permissiveness for C. burnetii. While maintaining cell viability, udder cells allowed the highest replication rates with formation of large cell-filling Coxiella containing vacuoles. Intestinal cells showed an enhanced susceptibility to invasion but supported C. burnetii replication only at intermediate levels. Lung and placental cells also internalized the bacteria but in strikingly smaller numbers. In any of the epithelial cells, both Coxiella strains failed to trigger a substantial IL-1β, IL-6 and TNF-α response. Epithelial cells, with mammary epithelial cells in particular, may therefore serve as a niche for C. burnetii replication in vivo without alerting the host’s immune response.

Robust growth of avirulent phase II Coxiella burnetii in bone marrow-derived murine macrophages

Published data show that murine bone marrow-derived macrophages (BMDM) restrict growth of avirulent phase II, but not virulent phase I, Coxiella burnetii. Growth restriction of phase II bacteria is thought to result from potentiated recognition of pathogen-associated molecular patterns, which leads to production of inhibitory effector molecules. Past studies have used conditioned medium from L-929 murine fibroblasts as a source of macrophage-colony stimulating factor (M-CSF) to promote differentiation of bone marrow-derived myeloid precursors into macrophages. However, uncharacterized components of conditioned medium, such as variable amounts of type I interferons, can affect macrophage activation status and their permissiveness for infection. In the current study, we show that the C. burnetii Nine Mile phase II (NMII) strain grows robustly in primary macrophages from C57BL/6J mice when bone marrow cells are differentiated with recombinant murine M-CSF (rmM-CSF). Bacteria were readily internalized by BMDM, and replicated within degradative, LAMP1-positive vacuoles to achieve roughly 3 logs of growth over 6 days. Uninfected BMDM did not appreciably express CD38 or Egr2, markers of classically (M1) and alternatively (M2) activated macrophages, respectively, nor did infection change the lack of polarization. In accordance with an M0 phenotype, infected BMDM produced moderate amounts of TNF and nitric oxide. Similar NMII growth results were obtained using C57BL/6J myeloid progenitors immortalized with an estrogen-regulated Hoxb8 (ER-Hoxb8) oncogene. To demonstrate the utility of the ER-Hoxb8 system, myeloid progenitors from natural resistance-associated macrophage protein 1 (Nramp1) C57BL/6J knock-in mice were transduced with ER-Hoxb8, and macrophages were derived from immortalized progenitors using rmM-CSF and infected with NMII. No difference in growth was observed when compared to macrophages from wild type mice, indicating depletion of metal ions by the Nramp1 transporter does not negatively impact NMII growth. Results with NMII were recapitulated in primary macrophages where C57BL/6J Nramp1+ BMDM efficiently killed Salmonella enterica serovar Typhimurium. M-CSF differentiated murine macrophages from bone marrow and conditional ER-Hoxb8 myeloid progenitors will be useful ex vivo models for studying Coxiella-macrophage interactions.

Phase variation of Coxiella burneti0i strain Priscilla: influence of this phenomenon on biochemical features of its lipopolysaccharide

During the phase variation of Coxiella burnetii, modifications in its lipopolysaccharide (LPS) component were investigated. The cloned phase I C. burnetii cells were passed serially in chicken embryo yolk sacs up to the egg passage (EP) 90. The LPSs from the cells in EPs 3, 12, 21, 40, 60, and 90 were all separated by steric exclusion chromatography into three major populations: the high, intermediate, and low molecular weight fractions, differing one from another in size and chemical composition. No noticeable shortening of the O-polysaccharide chains was observed in the LPSs isolated during the C. burnetii cultivation. However, a redistribution of the existing LPS populations has been observed due to an increasing prevalence of those cells in the whole cell population that express LPS molecules with truncated O-chains and those being of R-type. In the high and intermediate molecular weight LPS populations, virenose and dihydrohydroxystreptose are lost gradually with the progress in phase variation. This occurs more readily with the former sugar. At present, the molecular mechanisms influencing the LPS modifications during the C. burnetii phase variation remain unclear.

Right on Q: genetics begin to unravel Coxiella burnetii host cell interactions

Invasion of macrophages and replication within an acidic and degradative phagolysosome-like vacuole are essential for disease pathogenesis by Coxiella burnetii, the bacterial agent of human Q fever. Previous experimental constraints imposed by the obligate intracellular nature of Coxiella limited knowledge of pathogen strategies that promote infection. Fortunately, new genetic tools facilitated by axenic culture now allow allelic exchange and transposon mutagenesis approaches for virulence gene discovery. Phenotypic screens have illuminated the critical importance of Coxiella's type 4B secretion system in host cell subversion and discovered genes encoding translocated effector proteins that manipulate critical infection events. Here, we highlight the cellular microbiology and genetics of Coxiella and how recent technical advances now make Coxiella a model organism to study macrophage parasitism.

Coxiella burnetii lipopolysaccharide blocks p38α-MAPK activation through the disruption of TLR-2 and TLR-4 association

To survive in macrophages, Coxiella burnetii hijacks the activation pathway of macrophages. Recently, we have demonstrated that C. burnetii, via its lipopolysaccharide (LPS), avoids the activation of p38α-MAPK through an antagonistic engagement of Toll-like receptor (TLR)-4. We investigated the fine-tuned mechanism leading to the absence of activation of the p38α-MAPK despite TLR-4 engagement. In macrophages challenged with LPS from the avirulent variants of C. burnetii, TLR-4 and TLR-2 co-immunoprecipitated. This association was absent in cells challenged by the LPS of pathogenic C. burnetii. The disruption makes TLRs unable to signal during the recognition of the LPS of pathogenic C. burnetii. The disruption of TLR-2 and TLR-4 was induced by the re-organization of the macrophage cytoskeleton by C. burnetii LPS. Interestingly, blocking the actin cytoskeleton re-organization relieved the disruption of the association TLR-2/TLR-4 by pathogenic C. burnetii and rescued the p38α-MAPK activation by C. burnetii. We elucidated an unexpected mechanism allowing pathogenic C. burnetii to avoid macrophage activation by the disruption of the TLR-2 and TLR-4 association.

The sugar 3-deoxy-d-manno-oct-2-ulosonic acid (Kdo) as a characteristic component of bacterial endotoxin — a review of its biosynthesis, function, and placement in the lipopolysaccharide core

The sugar 3-deoxy-d-manno-oct-2-ulosonic acid (Kdo) is a characteristic component of bacterial lipopolysaccharide (LPS, endotoxin). It connects the carbohydrate part of LPS with C6 of glucosamine or 2,3-diaminoglucose of lipid A by acid-labile α-ketosidic linkage. The number of Kdo units present in LPS, the way they are connected, and the occurrence of other substituents (P, PEtn, PPEtn, Gal, or β-l-Ara4N) account for structural diversity of the inner core region of endotoxin. In a majority of cases, Kdo is crucial to the viability and growth of bacterial cells. In this paper, the biosynthesis of Kdo and the mechanism of its incorporation into the LPS structure, as well as the location of this unique component in the endotoxin core structures, have been described.

In silico biosynthesis of virenose, a methylated deoxy-sugar unique to Coxiella burnetii lipopolysaccharide

BACKGROUND

Coxiella burnetii is Gram-negative bacterium responsible for the zoonosis Q-fever. While it has an obligate intracellular growth habit, it is able to persist for extended periods outside of a host cell and can resist environmental conditions that would be lethal to most prokaryotes. It is these extracellular bacteria that are the infectious stage encountered by eukaryotic hosts. The intracellular form has evolved to grow and replicate within acidified parasitophorous vacuoles. The outer coat of C. burnetii comprises a complex lipopolysaccharide (LPS) component that includes the unique methylated-6-deoxyhexose, virenose. Although potentially important as a biomarker for C. burnetii, the pathway for its biosynthesis remains obscure.

RESULTS

The 6-deoxyhexoses constitute a large family integral to the LPS of many eubacteria. It is believed that precursors of the methylated-deoxyhexoses traverse common early biosynthetic steps as nucleotide-monosaccharides. As a prelude to a full biosynthetic characterization, we present herein the results from bioinformatics-based, proteomics-supported predictions of the pathway for virenose synthesis. Alternative possibilities are considered which include both GDP-mannose and TDP-glucose as precursors.

CONCLUSION

We propose that biosynthesis of the unique C. burnetii biomarker, virenose, involves an early pathway similar to that of other C-3'-methylated deoxysugars which then diverges depending upon the nucleotide-carrier involved. The alternatives yield either the D- or L-enantiomers of virenose. Both pathways require five enzymatic steps, beginning with either glucose-6-phosphate or mannose-6-phosphate. Our in silico results comprise a model for virenose biosynthesis that can be directly tested. Definition of this pathway should facilitate the development of therapeutic agents useful for treatment of Q fever, as well as allowing improvements in the methods for diagnosing this highly infectious disease.

Lipopolysaccharide of Coxiella burnetii

A lipopolysaccharide (LPS) is considered to be one of the major determinants of virulence expression and infection of virulent Coxiella burnetii. The LPSs from virulent phase I (LPS I) and from avirulent phase II (LPS II) bacteria were investigated for their chemical composition, structure and biological properties. LPS II is of rough (R) type in contrast to LPS I, which is phenotypically smooth (S) and contains a noticeable amount of two sugars virenose (Vir) and dihydrohydroxystreptose (Strep), which have not been found in other LPSs and can be considered as unique biomarkers of the bacterium. Both sugars were suggested to be located mostly in terminal positions of the O-specific chain of LPS I (O-PS I) and to be involved in the immunobiology of Q fever. There is a need to establish a more detailed chemical structure of LPS I in connection with prospective, deeper studies on mechanisms of pathogenesis and immunity of Q fever, its early and reliable diagnosis, and effective prophylaxis against the disease. This will also help to better understanding of host-pathogen interactions and contribute to improved modulation of pathological reactions which in turn are prerequisite for research and development of vaccines of new type. A fundamental understanding of C. burnetii LPS biosynthesis is still lacking. The intracellular nature of the bacterium, lack of genetic tools and its status as a selected agent have made elucidating basic physiological mechanisms challenging. The GDP-β-D-Vir biosynthetic pathway proposed most recently is an important initial step in this endeavour. The current advanced technologies providing the genetic tools necessary to screen C. burnetii mutants and propagate isogenic mutants might speed the discovery process.

Characterization of the GDP-D-mannose biosynthesis pathway in Coxiella burnetii: the initial steps for GDP-β-D-virenose biosynthesis

Coxiella burnetii, the etiologic agent of human Q fever, is a Gram-negative and naturally obligate intracellular bacterium. The O-specific polysaccharide chain (O-PS) of the lipopolysaccharide (LPS) of C. burnetii is considered a heteropolymer of the two unusual sugars β-D-virenose and dihydrohydroxystreptose and mannose. We hypothesize that GDP-D-mannose is a metabolic intermediate to GDP-β-D-virenose. GDP-D-mannose is synthesized from fructose-6-phosphate in 3 successive reactions; Isomerization to mannose-6-phosphate catalyzed by a phosphomannose isomerase (PMI), followed by conversion to mannose-1-phosphate mediated by a phosphomannomutase (PMM) and addition of GDP by a GDP-mannose pyrophosphorylase (GMP). GDP-D-mannose is then likely converted to GDP-6-deoxy-D-lyxo-hex-4-ulopyranose (GDP-Sug), a virenose intermediate, by a GDP-mannose-4,6-dehydratase (GMD). To test the validity of this pathway in C. burnetii, three open reading frames (CBU0671, CBU0294 and CBU0689) annotated as bifunctional type II PMI, as PMM or GMD were functionally characterized by complementation of corresponding E. coli mutant strains and in enzymatic assays. CBU0671, failed to complement an Escherichia coli manA (PMM) mutant strain. However, complementation of an E. coli manC (GMP) mutant strain restored capsular polysaccharide biosynthesis. CBU0294 complemented a Pseudomonas aeruginosa algC (GMP) mutant strain and showed phosphoglucomutase activity (PGM) in a pgm E. coli mutant strain. Despite the inability to complement a manA mutant, recombinant C. burnetii PMI protein showed PMM enzymatic activity in biochemical assays. CBU0689 showed dehydratase activity and determined kinetic parameters were consistent with previously reported data from other organisms. These results show the biological function of three C. burnetii LPS biosynthesis enzymes required for the formation of GDP-D-mannose and GDP-Sug. A fundamental understanding of C. burnetii genes that encode PMI, PMM and GMP is critical to fully understand the biosynthesic pathway of GDP-β-D-virenose and LPS structure in C. burnetii.

Proteomic comparison of virulent phase I and avirulent phase II of Coxiella burnetii, the causative agent of Q fever

Coxiella burnetii, a category B biological warfare agent, causes multiple outbreaks of the zoonotic disease Q fever world-wide, each year. The virulent phase I and avirulent phase II variants of the Nine Mile RSA 493 and 439 strains of C. burnetii were propagated in embryonated hen eggs and then purified by centrifugation through Renografin gradients. Total protein fractions were isolated from each phase and subjected to analysis by one-dimensional electrophoresis plus tandem mass spectrometry. A total of 235 and 215 non-redundant proteins were unambiguously identified from the phase I and II cells, respectively. Many of these proteins had not been previously reported in proteomic studies of C. burnetii. The newly identified proteins should provide additional insight into the pathogenesis of Q fever. Several of the identified proteins are involved in the biosynthesis and metabolism of components of the extracellular matrix. Forty-four of the proteins have been annotated as having distinct roles in the pathogenesis or survival of C. burnetii within the harsh phagolysosomal environment. We propose that nine enzymes specifically involved with lipopolysaccharide biosynthesis and metabolism, and that are distinctively present in phase I cells, are virulence-associated proteins.

Coxiella burnetii glycomics and proteomics--tools for linking structure to function

Coxiella burnetii, the causative agent of Q fever, is an obligate intracellular bacterium and a highly infectious pathogen. The disease is a widespread zoonosis and is endemic throughout the world. An easy aerosol dissemination, environmental persistence, and high infectivity make the bacterium a serious threat for humans and animals. Lipopolysaccharide is considered one of the major factors of virulence expression and infection of the bacterium. Detailed glycomic studies enabled to better understand structural and functional peculiarities of this biopolymer and its role in pathogenesis and immunity of Q fever. Recent proteomic studies of C. burnetii have brought new approaches in accurate detection of the infectious agent and offered new insights into the inter- or intra-species relatedness. Thus, structure/function relationship studies are currently of utmost importance in the field. This paper will focus on glycomic and proteomic approaches providing information on unique glycan and protein species of the microorganism as the candidate molecules for the use in detection/diagnosis, therapy, and prophylaxis.

Comparative genomics reveal extensive transposon-mediated genomic plasticity and diversity among potential effector proteins within the genus Coxiella

Genetically distinct isolates of Coxiella burnetii, the cause of human Q fever, display different phenotypes with respect to in vitro infectivity/cytopathology and pathogenicity for laboratory animals. Moreover, correlations between C. burnetii genomic groups and human disease presentation (acute versus chronic) have been described, suggesting that isolates have distinct virulence characteristics. To provide a more-complete understanding of C. burnetii's genetic diversity, evolution, and pathogenic potential, we deciphered the whole-genome sequences of the K (Q154) and G (Q212) human chronic endocarditis isolates and the naturally attenuated Dugway (5J108-111) rodent isolate. Cross-genome comparisons that included the previously sequenced Nine Mile (NM) reference isolate (RSA493) revealed both novel gene content and disparate collections of pseudogenes that may contribute to isolate virulence and other phenotypes. While C. burnetii genomes are highly syntenous, recombination between abundant insertion sequence (IS) elements has resulted in genome plasticity manifested as chromosomal rearrangement of syntenic blocks and DNA insertions/deletions. The numerous IS elements, genomic rearrangements, and pseudogenes of C. burnetii isolates are consistent with genome structures of other bacterial pathogens that have recently emerged from nonpathogens with expanded niches. The observation that the attenuated Dugway isolate has the largest genome with the fewest pseudogenes and IS elements suggests that this isolate's lineage is at an earlier stage of pathoadaptation than the NM, K, and G lineages.

Attenuated Coxiella burnetii phase II causes a febrile response in gamma interferon knockout and Toll-like receptor 2 knockout mice and protects against reinfection

Coxiella burnetii is a highly infectious obligate intracellular bacterium. The phase I form is responsible for Q fever, a febrile illness with flu-like symptoms that often goes undiagnosed. The attenuated C. burnetii phase II (having a truncated "O" chain of its lipopolysaccharide) does not cause disease in immunocompetent animals; however, phase II organisms remain infectious, and we questioned whether disease could be produced in immunodeficient mice. To study C. burnetii phase II infections, febrile responses in gamma interferon knockout (IFN-gamma(-/-)), BALB/c, Toll-like receptor 2 knockout (TLR2(-/-)), and C57BL/6 mice were measured using the Nine Mile phase II (NMII) strain of C. burnetii. Immunocompetent mice showed minimal febrile responses, unlike those obtained with IFN-gamma(-/-) and TLR2(-/-) mice, which showed elevated rectal temperatures that were sustained for approximately 15 days with transient increases in splenic weights. Reinfection of IFN-gamma(-/-) and TLR2(-/-) mice with C. burnetii NMII 30 days after primary infection protected mice as evident by reduced febrile responses and a lack of splenic inflammation. Although minimal detection of Coxiella in TLR2(-/-) mouse spleens was observed, greater colonization was evident in the IFN-gamma(-/-) mice. Cytokine analysis was performed on infected peritoneal macrophages isolated from these mice, and immunocompetent macrophages showed robust tumor necrosis factor alpha, IFN-gamma, and granulocyte-macrophage colony-stimulating factor (GM-CSF) but no interleukin-12 (IL-12) responses. IFN-gamma(-/-) macrophages produced elevated levels of IL-6, IL-10, and IL-12, while TLR2(-/-) macrophages produced GM-CSF, IL-12, and minimal IL-10. To distinguish immunity conferred by innate or adaptive systems, adoptive transfer studies were performed and showed that immune lymphocytes obtained from immunocompetent mice protected against a subsequent challenge with NMII, indicating that adaptive immunity mediates the observed protection. Thus, our data show that NMII is capable of eliciting disease in immunocompromised mice, which may help in evaluation of vaccine candidates as well as the study of host-pathogen interactions.

Structural and functional characterization of the glycan antigens involved in immunobiology of Q fever

Coxiella burnetii is the causative agent of Q fever. The bacterium is extremely infectious and is classified as a category biological weapon. A lipopolysaccharide I (LPS I) belongs to the main components of the C. burnetii outer membrane and its structure-function relationship studies are of potential interest. Size-exclusion chromatography revealed noticeable differences in distribution and chemical composition of the O-polysaccharide chains in LPS I. It is likely that C. burnetii is capable of synthesizing chemically distinct subclasses of O-specific polysaccharide molecules differing in their antigenic reactivities. Methylation-linkage analysis indicated the presence of terminal virenose (Vir), dihydrohydroxystreptose (Strep), and mannose (Man), 4-substituted Vir, and 4-substituted Man in the O-specific chain. Serological data indicate that Vir and Strep might be involved in the immunobiology of Q fever.

Genetic diversity of the Q fever agent, Coxiella burnetii, assessed by microarray-based whole-genome comparisons

Coxiella burnetii, a gram-negative obligate intracellular bacterium, causes human Q fever and is considered a potential agent of bioterrorism. Distinct genomic groups of C. burnetii are revealed by restriction fragment-length polymorphisms (RFLP). Here we comprehensively define the genetic diversity of C. burnetii by hybridizing the genomes of 20 RFLP-grouped and four ungrouped isolates from disparate sources to a high-density custom Affymetrix GeneChip containing all open reading frames (ORFs) of the Nine Mile phase I (NMI) reference isolate. We confirmed the relatedness of RFLP-grouped isolates and showed that two ungrouped isolates represent distinct genomic groups. Isolates contained up to 20 genomic polymorphisms consisting of 1 to 18 ORFs each. These were mostly complete ORF deletions, although partial deletions, point mutations, and insertions were also identified. A total of 139 chromosomal and plasmid ORFs were polymorphic among all C. burnetii isolates, representing ca. 7% of the NMI coding capacity. Approximately 67% of all deleted ORFs were hypothetical, while 9% were annotated in NMI as nonfunctional (e.g., frameshifted). The remaining deleted ORFs were associated with diverse cellular functions. The only deletions associated with isogenic NMI variants of attenuated virulence were previously described large deletions containing genes involved in lipopolysaccharide (LPS) biosynthesis, suggesting that these polymorphisms alone are responsible for the lower virulence of these variants. Interestingly, a variant of the Australia QD isolate producing truncated LPS had no detectable deletions, indicating LPS truncation can occur via small genetic changes. Our results provide new insight into the genetic diversity and virulence potential of Coxiella species.

Coxiella burnetii Whole Cell Lysate Protein Identification by Mass Spectrometry and Tandem Mass Spectrometry

The whole cell lysate of Coxiella burnetii strain RSA 493 was separated by two-dimensional electrophoresis and more than 500 protein spots were found on silver-stained reference map. Spots from the gels were subjected to identification based on peptide mass fingerprinting (PMF). In order to identify additional proteins, tandem mass spectrometry (MS/MS) using electrospray and matrix-assisted laser desorption/ionization techniques was applied. The three independent approaches resulted in the identification of 197 open reading frames (ORFs). Fifty-two proteins were identified by PMF and at least with one of the MS/MS methods, 37 proteins with both MS/MS instruments, and 19 proteins with all three techniques applied. All predicted C. burnetii ORFs were compared with the Clusters of Orthologous Groups database. The data related to identified proteins were stored and indexed in a file that can be read and searched using Microsoft Access.

Virulent Coxiella burnetii does not activate human dendritic cells: role of lipopolysaccharide as a shielding molecule

Coxiella burnetii is an obligate intracellular bacterium and the etiological agent of the zoonotic disease Q fever. Acute human Q fever is characterized by flu-like symptoms that, in some cases, can result in a persistent infection that may reactivate months or years after initial exposure. Mechanisms by which this obligate parasite evades clearance by the host immune response during persistent infection are unknown. Here, we characterized the interaction of C. burnetii with dendritic cells (DC), critical components of both innate and adaptive immunity. Human DC were infected with two isogenic C. burnetii strains that differ in LPS length. Infection by the Nine Mile phase I (NMI) strain, which is fully virulent and produces full-length LPS, did not result in DC maturation. In contrast, infection by the avirulent Nine Mile phase II strain, producing a severely truncated LPS, resulted in toll-like receptor 4-independent DC maturation and approximately 10-fold more IL-12 and TNF production. NMI did not actively inhibit DC maturation as NMI-infected DC subsequently matured if treated with Escherichia coli LPS or Nine Mile phase II. Furthermore, removal of LPS from NMI dramatically increased its ability to stimulate DC. We propose a model whereby LPS of virulent C. burnetii masks toll-like receptor ligands from innate immune recognition by DC, thereby allowing replication without significant maturation or inflammatory cytokine production. This immune evasion strategy may allow C. burnetii to persist in an immunocompetent host.

Efficient chemical synthesis of both anomers of ADP L-glycero- and D-glycero-D-manno-heptopyranose

A series of anomeric phosphates and ADP-activated L-glycero- and D-glycero-D-manno-heptopyranoses has been prepared in high overall yields, which provided model compounds and substrates in the elucidation of biosynthetic pathways and glycosyl transfer reactions of nucleotide-activated bacterial heptoses. The alpha-anomers of the heptosyl phosphates were obtained in high yield and selectivity using the phosphoramidite procedure, whereas the beta-phosphates were formed preferentially employing acylation of reducing heptoses with diphenyl phosphorochloridate. An efficient route to the formation of the nucleotide diphosphate sugars was elaborated by coupling of the O-acetylated phosphates with AMP-morpholidate followed by alkaline deprotection to furnish ADP-L- and D-glycero-alpha-D-manno-heptose in 84 and 89% yield, respectively. Deacetylation of the O-acetylated beta-configured ADP heptoses was conducted at strictly controlled conditions (-28 degrees C at pH 10.5) to suppress formation of cyclic heptose-1,2-phosphodiesters with concomitant release of AMP. Isolation of the unstable beta-configured ADP-heptoses by anion-exchange chromatography and gel-filtration afforded ADP L- and D-glycero-beta-D-manno-heptose in high yields.

Lipopolysaccharide fromCoxiella burnetiiIs Involved in Bacterial Phagocytosis, Filamentous Actin Reorganization, and Inflammatory Responses through Toll-Like Receptor 4

The role of Toll-like receptors (TLRs) in the recognition of extracellular and facultative intracellular bacteria by the innate immune system has been extensively studied, but their role in the recognition of obligate intracellular organisms remains unknown. Coxiella burnetii, the agent of Q fever, is an obligate intracellular bacterium that specifically inhabits monocytes/macrophages. We showed in this study that C. burnetii LPS is involved in the uptake of virulent organisms by macrophages but not in that of avirulent variants. The uptake of virulent organisms was dependent on TLR4 because it was reduced in macrophages from TLR4(-/-) mice. In addition, LPS was responsible for filamentous actin reorganization induced by virulent C. burnetii, which was prevented in TLR4(-/-) macrophages. In contrast, the intracellular fate of C. burnetii was not affected in TLR4(-/-) macrophages, suggesting that TLR4 does not control the maturation of C. burnetii phagosome and the microbicidal activity of macrophages. These results are consistent with in vivo experiments because the pattern of tissue infection and the clearance of C. burnetii were similar in wild-type and TLR4(-/-) mice. We also showed that the number of granulomas was decreased in the liver of infected TLR4(-/-) mice, and the formation of splenic granulomas was only transient. The impaired formation of granulomas was associated with decreased production of IFN-gamma and TNF. Taken together, these results demonstrate that TLR4 controls early events of C. burnetii infection such as macrophage phagocytosis, granuloma formation, and cytokine production.

Physicochemical characterization of the endotoxins from Coxiella burnetii strain Priscilla in relation to their bioactivities

BACKGROUND

Coxiella burnetii is the etiological agent of Q fever found worldwide. The microorganism has like other Gram-negative bacteria a lipopolysaccharide (LPS, endotoxin) in its outer membrane, which is important for the pathogenicity of the bacteria. In order to understand the biological activity of LPS, a detailed physico-chemical analysis of LPS is of utmost importance.

RESULTS

The lipid A moiety of LPS is tetraacylated and has longer (C-16) acyl chains than most other lipid A from enterobacterial strains. The two ester-linked 3-OH fatty acids found in the latter are lacking. The acyl chains of the C. burnetii endotoxins exhibit a broad melting range between 5 and 25 degrees C for LPS and 10 and 40 degrees C for lipid A. The lipid A moiety has a cubic inverted aggregate structure, and the inclination angle of the D-glucosamine disaccharide backbone plane of the lipid A part with respect to the membrane normal is around 40 degrees. Furthermore, the endotoxins readily intercalate into phospholipid liposomes mediated by the lipopolysaccharide-binding protein (LBP). The endotoxin-induced tumor necrosis factor alpha (TNFalpha) production in human mononuclear cells is one order of magnitude lower than that found for endotoxins from enterobacterial strains, whereas the same activity as in the latter compounds is found in the clotting reaction of the Limulus amebocyte lysate assay.

CONCLUSIONS

Despite a considerably different chemical primary structure of the C. burnetii lipid A in comparison with enterobacterial lipid A, the data can be well understood by applying the previously presented conformational concept of endotoxicity, a conical shape of the lipid A moiety of LPS and a sufficiently high inclination of the sugar backbone plane with respect to the membrane plane. Importantly, the role of the acyl chain fluidity in modulating endotoxicity now becomes more evident.

Phase variation analysis of Coxiella burnetii during serial passage in cell culture by use of monoclonal antibodies

Antigenic changes in Coxiella burnetii Nine Mile strain phase I during serial passages in cell culture were analyzed with three groups of monoclonal antibodies (MAbs) against lipopolysaccharide. The MAbs of group 1 did not react with organisms that were passaged over five times, and the MAbs of group 2 did not react with organisms that were passaged over eight times. The MAbs of group 3 reacted with organisms passaged up to 15 times but did not react with phase II cells. These results suggest that C. burnetii could be differentiated into four phase states during phase variation.

Structural analyses of the lipopolysaccharides from Chlamydophila psittaci strain 6BC and Chlamydophila pneumoniae strain Kajaani 6

Lipopolysaccharides (LPSs) of Chlamydophila psittaci 6BC and Chlamydophila pneumoniae Kajaani 6 contain 3-deoxy-D-manno-oct-2-ulosonic acid (Kdo), GlcN, organic bound phosphate, and fatty acids in the molar ratios of approximately 3:2:2.2:4.8 and approximately 2.9:2:2.1:4.9, respectively. The LPSs were immunoreactive with a monoclonal antibody against a family-specific epitope of chlamydial LPS. This finding, together with methylation analyses of both LPSs and MALDI-TOF MS experiments on de-O-, and de-O,N-acylated LPSs, indicate the presence of a Kdo trisaccharide proximal to lipid A having a structure alpha-Kdo-(2-->8)-alpha-Kdo-(2-->4)-alpha-Kdo, which appears to be the main component of the core region in the native chlamydial LPSs. In the de-O-acylated LPSs from Chl. psittaci 6BC and Chl. pneumoniae Kajaani 6, two major molecular species are present that differ in distribution of amide-bound hydroxy fatty acids over both GlcN. It appears that either two (R)-3-hydroxy-18-methylicosanoic acids or one (R)-3-hydroxy-18-methylicosanoic acid and one (R)-3-hydroxyicosanoic acid are attached to the GlcN residues. In contrast, the de-O-acylated LPS of Chl. psittaci PK 5082 contains one major molecular species that has two (R)-3-hydroxyicosanoic acid residues attached to two GlcN residues.

alpha(v)beta(3) integrin and bacterial lipopolysaccharide are involved in Coxiella burnetii-stimulated production of tumor necrosis factor by human monocytes

Coxiella burnetii, the agent of Q fever, enters human monocytes through alpha(v)beta(3) integrin and survives inside host cells. In addition, C. burnetii stimulates the synthesis of inflammatory cytokines including tumor necrosis factor (TNF) by monocytes. We studied the role of the interaction of C. burnetii with THP-1 monocytes in TNF production. TNF transcripts and TNF release reached maximum values within 4 h. Almost all monocytes bound C. burnetii after 4 h, while the percentage of phagocytosing monocytes did not exceed 20%. Cytochalasin D, which prevented the uptake of C. burnetii without interfering with its binding, did not affect the expression of TNF mRNA. Thus, bacterial adherence, but not phagocytosis, is necessary for TNF production by monocytes. The monocyte alpha(v)beta(3) integrin was involved in TNF synthesis since peptides containing RGD sequences and blocking antibodies against alpha(v)beta(3) integrin inhibited TNF transcripts induced by C. burnetii. Nevertheless, the cross-linking of alpha(v)beta(3) integrin by specific antibodies was not sufficient to induce TNF synthesis. The signal delivered by C. burnetii was triggered by bacterial lipopolysaccharide (LPS). Polymyxin B inhibited the TNF production stimulated by C. burnetii, and soluble LPS isolated from C. burnetii largely mimicked viable bacteria. On the other hand, avirulent variants of C. burnetii induced TNF production through an increased binding to monocytes rather than through the potency of their LPS. We suggest that the adherence of C. burnetii to monocytes via alpha(v)beta(3) integrin enables surface LPS to stimulate TNF production in THP-1 monocytes.

Intraspecies diversity of Coxiella burnetii as revealed by com1 and mucZ sequence comparison

Coxiella burnetii is classified within the gamma subgroup of the Proteobacteria. All strains tested to date have an identical 16S rRNA sequence but 20 different genotypes have been determined by pulsed field gel electrophoresis (PFGE). In this study, intraspecies genetic diversity was investigated by sequence comparison of 715 bp of the Com1 encoding gene (com1) and 774 bp of the MucZ encoding gene (mucZ) in 37 strains isolated from animals and humans with acute or chronic Q fever in Europe, North America and Africa. Five and four groups were established from sequence analysis of com1 and mucZ, respectively. Neither relation of the defined groups to geographical distribution of the isolates was noted nor relation to disease form (acute/chronic). The same isolates were grouped together regardless of the gene being investigated. Comparison of the five proposed groups to previous groups, yielded after digestion by NotI PFGE, allowed for an intermediate classification of C. burnetii isolates between those obtained by using 16S rDNA (one group) and PFGE (20 groups).