Permeability of Coxiella burnetii to ribonucleosides

Multiple Substrate Usage of Coxiella burnetii to Feed a Bipartite Metabolic Network

The human pathogen Coxiella burnetii causes Q-fever and is classified as a category B bio-weapon. Exploiting the development of the axenic growth medium ACCM-2, we have now used ¹³C-labeling experiments and isotopolog profiling to investigate the highly diverse metabolic network of C. burnetii. To this aim, C. burnetii RSA 439 NMII was cultured in ACCM-2 containing 5 mM of either [U-¹³C₃]serine, [U-¹³C₆]glucose, or [U-¹³C₃]glycerol until the late-logarithmic phase. GC/MS-based isotopolog profiling of protein-derived amino acids, methanol-soluble polar metabolites, fatty acids, and cell wall components (e.g., diaminopimelate and sugars) from the labeled bacteria revealed differential incorporation rates and isotopolog profiles. These data served to decipher the diverse usages of the labeled substrates and the relative carbon fluxes into the core metabolism of the pathogen. Whereas, de novo biosynthesis from any of these substrates could not be found for histidine, isoleucine, leucine, lysine, phenylalanine, proline and valine, the other amino acids and metabolites under study acquired ¹³C-label at specific rates depending on the nature of the tracer compound. Glucose was directly used for cell wall biosynthesis, but was also converted into pyruvate (and its downstream metabolites) through the glycolytic pathway or into erythrose 4-phosphate (e.g., for the biosynthesis of tyrosine) via the non-oxidative pentose phosphate pathway. Glycerol efficiently served as a gluconeogenetic substrate and could also be used via phosphoenolpyruvate and diaminopimelate as a major carbon source for cell wall biosynthesis. In contrast, exogenous serine was mainly utilized in downstream metabolic processes, e.g., via acetyl-CoA in a complete citrate cycle with fluxes in the oxidative direction and as a carbon feed for fatty acid biosynthesis. In summary, the data reflect multiple and differential substrate usages by C. burnetii in a bipartite-type metabolic network, resembling the overall topology of the related pathogen Legionella pneumophila. These strategies could benefit the metabolic capacities of the pathogens also as a trait to adapt for replication under intracellular conditions.

Early cytokine and antibody responses against Coxiella burnetii in aerosol infection of BALB/c mice

Coxiella burnetii, a Gram-negative intracellular bacterium, can give rise to Q fever in humans and is transmitted mainly by inhalation of infected aerosols from animal reservoirs. Serology is commonly used to diagnose Q fever, but the early cellular immune response-i.e., C. burnetii-specific interferon γ (IFN-γ) production in response to antigen challenge-might be an additional diagnostic. Detection of IFN-γ responses has been used to identify past and chronic Q fever infections, but the IFN-γ response in acute Q fever has not been described. By challenging immunocompetent BALB/c mice with aerosols containing phase I C. burnetii, the timing and extent of IFN-γ recall responses were evaluated in an acute C. burnetii infection. Other cytokines were also measured in an effort to identify other potential diagnostic markers. The data show that after initial expansion of bacteria first in lungs and then in other tissues, the infection was cleared from day 10 onwards as reflected by the decreasing number of bacteria. The antigen-induced IFN-γ production by splenocytes coincided with emergence of IgM phase II antibodies at day 10 postinfection and preceded appearance of IgG antibodies. This was accompanied by the production of proinflammatory cytokines including interleukin (IL) 6, keratinocyte-derived cytokine, and IFN-γ-induced protein 10, followed by monocyte chemotactic protein 1, but not by IL-1β and tumor necrosis factor α, and only very low production of the anti-inflammatory cytokine IL-10. These data suggest that analysis of antigen-specific IFN-γ responses could be a useful tool for diagnosis of acute Q fever. Moreover, the current model of C. burnetii infection could be used to give new insights into immunological factors that predispose to development of persistent infection.

Virulence of pathogenic Coxiella burnetii strains after growth in the absence of host cells

Coxiella burnetii is a gram-negative bacterium that causes the zoonotic disease Q fever. Traditionally considered an obligate intracellular agent, the requirement to be grown in tissue culture cells, embryonated eggs, or animal hosts has made it difficult to isolate strains and perform genetic studies on C. burnetii. However, it was recently demonstrated that the attenuated Nine Mile Phase 2 (NM2) C. burnetii strain will grow axenically in acidified citrate cysteine medium (ACCM) in a 2.5% oxygen environment. The current study was undertaken to determine whether more virulent C. burnetii strains could be grown in ACCM, and whether virulence would be maintained after passage. The ACCM medium supported an ?1000-fold expansion of Nine Mile Phase 1 (NM1), NM2, M44, and Henzerling strains of C. burnetii, whereas the Priscilla (Q177) strain expanded only 100-fold, and the K strain (Q154) grew poorly in ACCM. To determine if passage in ACCM would maintain the virulence of C. burnetii, the NM1 strain was grown for up to 26 weekly passages in ACCM. C. burnetii maintained in ACCM for 5 or 8 passages maintained full virulence in a mouse model, but NM1 passaged for 23 or 26 times was somewhat attenuated. These data demonstrate that virulent strains of C. burnetii can be successfully passaged in ACCM; however, some strains can lose virulence after extended passage, and other strains grow poorly in this medium. The loss of virulence in axenic culture was associated with some truncation of lipopolysaccharide chains, suggesting a possible mechanism for attenuation.

Strain and phase identification of the U.S. category B agent Coxiella burnetii by matrix assisted laser desorption/ionization time-of-flight mass spectrometry and multivariate pattern recognition

Accurate bacterial identification is important in diagnosing disease and in microbial forensics. Coxiella burnetii, a highly infective microorganism causative of the human disease Q fever, is now considered a U.S. category B potential bioterrorism agent. We report here an approach for the confirmatory identification of C. burnetii at the strain level which involves the combined use of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) and supervised pattern recognition via Partial Least Squares-Discriminant Analysis (PLS-DA). C. burnetii isolates investigated in this study included the following prototype strains from different geographical and/or historical origins and with different antigenic properties: Nine Mile I, Australian QD, M44, KAV, PAV, Henzerling, and Ohio. After culture and purification following standard protocols, linear MALDI-TOF mass spectra of pure bacterial cultures were acquired in positive ion mode. Mass spectral data were normalized, baseline-corrected, denoised, binarized and modeled by PLS-DA under crossvalidation conditions. Robustness with respect to uncontrolled variations in the sample preparation and MALDI analysis protocol was assessed by repeating the experiment on five different days spanning a period of 6 months. The method was validated by the prediction of unknown C. burnetii samples in an independent test set with 100% sensitivity and specificity for five out of six strain classes.

A growth study of Coxiella burnetii Nine Mile Phase I and Phase II in fibroblasts

Coxiella burnetii, a slow-growing, gram-negative, obligate intracellular bacterium, is the causative agent of Q fever in humans. The avirulent Phase II C. burnetii Nine Mile strain can invade and establish persistent infections in a wide variety of laboratory cell lines, and is generally considered to be easier to grow in culture than the wild-type Phase I organism. Efforts to improve Phase I organism yield in the BHK-21 cell line demonstrated that high CO2 conditions and the use of Dulbecco's modified Eagle's medium (DMEM) with 4.5 g/l glucose supplementation resulted in higher organism yields. Phase II organisms grown in the same cell line and conditions showed lower growth rates. Analysis revealed that increased average numbers of C. burnetii Phase I organisms within fibroblasts was due to higher growth rates within the hosts rather than to increased uptake or to increased cell-to-cell spreading. Addition of the nucleoside cytidine to the growth medium stimulated growth of Phase II but not Phase I organisms.

Identification of Biomarkers of Whole Coxiella burnetii Phase I by MALDI-TOF Mass Spectrometry

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) specific biomarkers have been shown to be an effective tool for identifying microorganisms. In this study, we demonstrate the feasibility of using this technique to detect the obligate intracellular bacterium Coxiella burnetii, a category B bioterrorism agent. Specific biomarkers were detected in C. burnetii Nine Mile phase I (NMI) strain purified from embryonated egg yolk sac preparations. Whole organisms were applied directly to the MALDI target. MALDI-TOF MS analysis of C. burnetii NMI grown and purified at different times and places revealed a group of unique, characteristic, and reproducible spectral markers in the mass range of 1000-25000 Da. Statistical analysis of the averaged centroided masses uncovered at least 24 peptides or biomarkers. Three biomarkers observed in the MALDI-TOF MS spectrum consistently matched proteins that had been previously described in C. burnetii, one of them being the small cell variant protein A. MALDI-TOF MS analysis of whole organisms represents a sensitive and specific option for characterizing C. burnetii isolates, especially when coupled with antigen capture techniques. The method also has potential for several applications in basic microbial research, including regulation of gene expression.

Complete genome sequence of the Q-fever pathogen Coxiella burnetii

The 1,995,275-bp genome of Coxiella burnetii, Nine Mile phase I RSA493, a highly virulent zoonotic pathogen and category B bioterrorism agent, was sequenced by the random shotgun method. This bacterium is an obligate intracellular acidophile that is highly adapted for life within the eukaryotic phagolysosome. Genome analysis revealed many genes with potential roles in adhesion, invasion, intracellular trafficking, host-cell modulation, and detoxification. A previously uncharacterized 13-member family of ankyrin repeat-containing proteins is implicated in the pathogenesis of this organism. Although the lifestyle and parasitic strategies of C. burnetii resemble that of Rickettsiae and Chlamydiae, their genome architectures differ considerably in terms of presence of mobile elements, extent of genome reduction, metabolic capabilities, and transporter profiles. The presence of 83 pseudogenes displays an ongoing process of gene degradation. Unlike other obligate intracellular bacteria, 32 insertion sequences are found dispersed in the chromosome, indicating some plasticity in the C. burnetii genome. These analyses suggest that the obligate intracellular lifestyle of C. burnetii may be a relatively recent innovation.