Cloning, sequencing and expression of the dnaJ gene of Coxiella burnetii

Cloning, expression, and characterization of a Coxiella burnetii Cu/Zn Superoxide dismutase

Background

Periplasmically localized copper-zinc co-factored superoxide dismutase (SodC) enzymes have been identified in a wide range of Gram-negative bacteria and are proposed to protect bacteria from exogenously produced toxic oxygen radicals, which indicates the potential significance of a Coxiella burnetii SodC.

Results

Assays for SOD activity demonstrated that the cloned C. burnetii insert codes for a SOD that was active over a wide range of pH and inhibitable with 5 mM H₂O₂ and 1 mM sodium diethyldithiocarbamate, a characteristic of Cu/ZnSODs that distinguishes them from Fe or Mn SODs. The sodC was expressed by C. burnetii, has a molecular weight of approximately 18 kDa, which is consistent with the predicted molecular weight, and localized towards the periphery of C. burnetii. Over expression of the C. burnetii sodC in an E. coli sodC mutant restored resistance to H₂O₂ killing to wild type levels.

Conclusions

We have demonstrated that C. burnetii does express a Cu/ZnSOD that is functional at low pH, appears to be excreted, and was able to restore H₂O₂ resistance in an E. coli sodC mutant. Taken together, these results indicate that the C. burnetii Cu/ZnSOD is a potentially important virulence factor.

Detection of Coxiella burnetii by PCR in mice after administration of live M-44 vaccine

Original primers were prepared for the detection of coxiella burnetii by PCR for the amplification of a 752-bp fragment of dnaJ gene. Using these primers we observed the persistence of C. burnetii in different organs of mice after the administration of live Q-fever vaccine over a 7-months period.

Q fever epidemiology and pathogenesis

The lungs are a port of entry and primary infectious focus of Coxiella burnetii, the obligate intracellular contagium of the worldwide zoonosis Q fever. The infectious process and immune response are characterised by studies in cell culture and animal systems. Following endocytosis, replication exclusively occurs in the phagolysosome. Several potential virulence factors are described.

Expression of beta-lactamase in Coxiella burnetii transformants

Coxiella burnetii can be transformed to ampicillin resistance by electroporation with plasmids encoding beta-lactamase. However, non-plasmid emergence of resistance to ampicillin also develops. To validate the usefulness of the bla gene marker for selection and detection, transformed C. burnetii were examined for beta-lactamase expression by use of immunoblotting after SDS-PAGE. The 29-kDa mature form of the beta-lactamase protein was detected in C. burnetii lysates. Quantitation of these immunoblot signals showed that C. burnetii surprisingly expressed low levels of beta-lactamase. The results validate the use of plasmid-encoded ampicillin resistance as a means for selecting C. burnetii transformants; they also suggest that levels of ampicillin used for selection pressure should be empirically determined and that detection of beta-lactamase by antibody blotting done to confirm transformants.

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).

Q fever

Q fever is a zoonosis with a worldwide distribution with the exception of New Zealand. The disease is caused by Coxiella burnetii, a strictly intracellular, gram-negative bacterium. Many species of mammals, birds, and ticks are reservoirs of C. burnetii in nature. C. burnetii infection is most often latent in animals, with persistent shedding of bacteria into the environment. However, in females intermittent high-level shedding occurs at the time of parturition, with millions of bacteria being released per gram of placenta. Humans are usually infected by contaminated aerosols from domestic animals, particularly after contact with parturient females and their birth products. Although often asymptomatic, Q fever may manifest in humans as an acute disease (mainly as a self-limited febrile illness, pneumonia, or hepatitis) or as a chronic disease (mainly endocarditis), especially in patients with previous valvulopathy and to a lesser extent in immunocompromised hosts and in pregnant women. Specific diagnosis of Q fever remains based upon serology. Immunoglobulin M (IgM) and IgG antiphase II antibodies are detected 2 to 3 weeks after infection with C. burnetii, whereas the presence of IgG antiphase I C. burnetii antibodies at titers of >/=1:800 by microimmunofluorescence is indicative of chronic Q fever. The tetracyclines are still considered the mainstay of antibiotic therapy of acute Q fever, whereas antibiotic combinations administered over prolonged periods are necessary to prevent relapses in Q fever endocarditis patients. Although the protective role of Q fever vaccination with whole-cell extracts has been established, the population which should be primarily vaccinated remains to be clearly identified. Vaccination should probably be considered in the population at high risk for Q fever endocarditis.

Codon usage and nucleotide composition in Coxiella burnetii

Coxiella burnetii, the causative agent of Q fever, is an obligate intracellular bacterium. With the development of molecular biology techniques, there have been increasing efforts on gene cloning and other genetic analyses of this organism. In this report, we tabulate the codon usage (CU) and nucleotide (nt) co-occurrence in C. burnetii, based on available nt sequence data. The average G+C content of the C. burnetii genome is 42.4%, where the G+C content is 42.7% for the chromosome and 38.7% for the plasmid. In comparison to Escherichia coli, there is biased CU. Some codons are frequently used in C. burnetii, but rarely used in E. coli and vice versa. Plasmid genes prefer A or T at the first or third position of a codon. However, TAA remains the most used stop codon. In the AT-rich DNA of C. burnetii, A or T tend to occur together, forming A or T tracks.

The sequences of heat shock protein 40 (DnaJ) homologs provide evidence for a close evolutionary relationship between the Deinococcus-thermus group and cyanobacteria

The genes encoding for heat shock protein 40 (Hsp40 or DnaJ) homologs were cloned and sequenced from the archaebacterium Halobacterium cutirubrum and the eubacterium Deinococcus proteolyticus to add to sequences from the gene banks. These genes were identified downstream of the Hsp70 (or DnaK) genes in genomic fragments spanning this region and, as in other prokaryotic species, Hsp70-Hsp40 genes are likely part of the same operon. The Hsp40 homolog from D. proteolyticus was found to be lacking a central 204 base pair region present in H. cutirubrum that encodes for the four cysteine-rich domains of the repeat consensus sequence CxxCxGxG (where x is any amino acid), present in most Hsp40 homologs. The available sequences from various archaebacteria, eubacteria, and eukaryotes show that the same deletion is also present in the homologs from Thermus aquaticus and two cyanobacteria, but in no other species tested. This unique deletion and the clustering of homologs from the Deinococcus-Thermus group and cyanobacterial species in the Hsp40 phylogenetic trees suggest a close evolutionary relationship between these groups as was also shown recently for Hsp70 sequences (R.S. Gupta et al., J Bacteriol 179:345-357, 1997). Sequence comparisons indicate that the Hsp40 homologs are not as conserved as the Hsp70 sequences. Phylogenetic analysis provides no reliable information concerning evolutionary relationship between prokaryotes and eukaryotes and their usefulness in this regard is limited. However, in phylogenetic trees based on Hsp40 sequences, the two archaebacterial homologs showed a polyphyletic branching within Gram-positive bacteria, similar to that seen with Hsp70 sequences.

Genetics of Coxiella burnetii

Those organisms considered to be obligate intracellular bacteria are interesting objects for genetic studies. Little is known about their mechanisms for natural genetic exchange. Many genes from the bacterium Coxiella burnetii, an obligate intraphagolysosomal pathogen, have therefore been cloned and characterized using the heterologous host Escherichia coli. Recently, use of electroporation methodology followed by long-term selection periods have provided initial data on genetic transformation in C. burnetii.

Analysis of a Coxiella burnetti gene product that activates capsule synthesis in Escherichia coli: requirement for the heat shock chaperone DnaK and the two-component regulator RcsC

A 1.2-kb EcoRI genomic DNA fragment of Coxiella burnetti, when cloned onto a multicopy plasmid, was found to induce capsule synthesis (mucoidy) in Escherichia coli. Nucleotide sequence analysis revealed the presence of an open reading frame that could encode a protein of 270 amino acids. Insertion of a tet cassette into a unique NruI restriction site resulted in the loss of induction of mucoidy. Because of its ability to induce mucoidy, we designated this gene mucZ. Computer search for homologies to mucZ revealed 42% identity to an open reading frame located at 1 min of the E. coli chromosome. Interestingly, the C-terminal amino acid residues of MucZ share significant homology with the J domain of the DnaJ protein and its homologs, suggesting potential interactions between MucZ and components of the DnaK-chaperone machinery. Results presented in this paper suggest that E. coli requires DnaK-chaperone machinery for Lon-RcsA-mediated induction of capsule synthesis, as noticed first by S. Gottesman (personal communication). The induction caused by MucZ is independent of Lon-RcsA and is mediated through the two-component regulators RcsC and RcsB. DnaK and GrpE but not DnaJ are also required for the RcsB-mediated MucZ induction, and we propose that MucZ is a DnaJ-like chaperone protein that might be required for the formation of an active RcsA-RcsB complex and for the RcsC-dependent phosphorylation of RcsB. Discussions are presented that suggest three different roles for alternative forms of the DnaK-chaperone machinery in capsule production.