A sporulation gene in Coxiella burnetii?

Morphological remodeling of Coxiella burnetii during its biphasic developmental cycle revealed by cryo-electron tomography

Coxiella burnetii is an obligate zoonotic bacterium that targets macrophages causing a disease called Q fever. It has a biphasic developmental life cycle where the extracellular and metabolically inactive small cell variant (SCV) transforms inside the host into the vegetative large cell variant (LCV). However, details about the morphological and structural changes of this transition are still lacking. Here, we used cryo-electron tomography to image both SCV and LCV variants grown either under axenic conditions or purified directly from host cells. We show that SCVs are characterized by equidistant stacks of inner membrane that presumably facilitate the transition to LCV, a transition coupled with the expression of the Dot/Icm type IVB secretion system (T4BSS). A class of T4BSS particles were associated with extracellular densities possibly involved in host infection. Also, SCVs contained spherical multilayered membrane structures of different sizes and locations suggesting no connection to sporulation as once assumed.

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.

Long-term persistence of Coxiella burnetii after acute primary Q fever

BACKGROUND

Long-term persistence of C. burnetii in infected animals was established in the 1950s and 60s, but the implications for human Q fever are not fully explored.

AIM

To compare the prevalence of markers of infection in a cohort of Q fever patients in Australia (up to 5 years after infection) with those in the 1989 Birmingham cohort (12 years after infection).

DESIGN

Case follow-up study.

METHODS

C. burnetii was tested for by: (i) antibodies to Phase 1 and 2 antigens in the three immunoglobulin classes; (ii) detection of DNA in bone marrow and peripheral blood mononuclear cells by PCR assays directed against several different targets in the genome; and (iii) attempts to isolate coxiellas in cell culture or mice from PCR-positive samples. Amplicon specificity was verified by fluorometric probing and by sequencing. Cross-contamination was excluded by extensive use of non-template controls, and in particular by the use of certain IS1111a target sequences.

RESULTS

Irrespective of clinical state, both groups remained seropositive, principally exhibiting medium levels of IgG antibody against C. burnetii Phase 2 antigen. C. burnetii genomic DNA was detected by PCR in 65% of bone marrow aspirates from Australian patients and approximately 88% of Birmingham patients. No coxiella were isolated from PCR positive samples.

DISCUSSION

We propose a provisional model for persistence. In Q fever without sequelae, the process is largely confined to the bone marrow. In Q fever fatigue syndrome (QFS), it is modulated by the patient's immunogenetic background to give higher levels of coxiella genomes in bone marrow and increased shedding into the peripheral blood. In Q fever endocarditis, late pregnancy, or during iatrogenic or other immunosuppression, the multiplication cycle is prolonged, and a potential source of live organisms.

Mutational analysis of the tra locus of the broad-host-range Streptomyces plasmid pIJ101

The tra gene of Streptomyces lividans plasmid pIJ101 encodes a 621-amino-acid protein that can mediate both plasmid transfer and the interbacterial transfer of chromosomal genes (i.e., chromosome-mobilizing ability [Cma]) during mating. Here we report the results of in-frame insertional mutagenesis studies aimed at defining regions of Tra required for these functions. While hexameric linker insertions throughout the tra gene affected plasmid and chromosomal gene transfer, insertions in a 200-amino-acid region of the Tra protein that contains presumed nucleotide-binding motifs and that is widely conserved among a functionally diverse family of bacterial and plasmid proteins (K. J. Begg, S. J. Dewar, and W. D. Donachie, J. Bacteriol. 177:6211-6222, 1995) had especially prominent effects on both functions. Insertions near the N terminus of Tra reduced Cma for either circular or linear host chromosomes to a much greater extent than pIJ101 plasmid transfer. Our results suggest that Cma involves Tra functions incremental to those needed for plasmid DNA transfer.

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.

Nucleotide sequence and characterization of cdrA, a cell division-related gene of Helicobacter pylori

We identified cell division-related gene cdrA in Helicobacter pylori HPK5. The putative gene product, CdrA, is a 367-amino-acid polypeptide that exhibited a high level of homology to conserved hypothetical ATP-binding protein HP0066 of H. pylori 26695, except in the N-terminal region, and showed some similarity to the FtsK/SpoIIIE family proteins. We isolated a cdrA-disrupted mutant by allelic exchange mutagenesis. Because of the low transformation frequency, the possibility that a suppressing mutation would be found in the obtained cdrA mutant was discussed. A repressive role for CdrA on cell division was suggested by the observations that the wild-type strain formed filamentous cells in a high-salt level medium at early stationary phase, while a cdrA-disrupted mutant did not show such an abnormality. In addition, the wild-type strain adopted coccoid forms in the stationary phase, whereas the cdrA-disrupted mutant remained mostly as short rods. Furthermore, the cdrA-disrupted mutant regained the filamentation phenotype when the intact cdrA gene was introduced by allelic exchange. Taken together, these observations show that the cdrA gene plays an important role in the cell growth of H. pylori.

Whole sequence of spoIIIE-like, sporulation-inhibitory, and transfer gene (spi) in a conjugative plasmid, pSA1.1, of Streptomyces azureus and detection of spi-like gene in the actinomycete chromosome

The nucleotide sequence of spoIIIE-like and the sporulation-inhibitory and transfer gene (spi) in a conjugative plasmid, pSA1.1, of Streptomyces azureus were examined to detect the promoter region. Using Southern blotting and a spi fragment as probe, spi-like genes were detected in chromosomes of the host and other actinomycetes. These results suggest that there is a spi- and spoIIIE-like gene in chromosomes of some actinomycetes.

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 C-terminal extension of yeast seryl-tRNA synthetase affects stability of the enzyme and its substrate affinity

Saccharomyces cerevisiae seryl-tRNA synthetase (SerRS) contains a 20-amino acid C-terminal extension, which is not found in prokaryotic SerRS enzymes. A truncated yeast SES1 gene, lacking the 60 base pairs that encode this C-terminal domain, is able to complement a yeast SES1 null allele strain; thus, the C-terminal extension in SerRS is dispensable for the viability of the cell. However, the removal of the C-terminal peptide affects both stability of the enzyme and its affinity for the substrates. The truncation mutant binds tRNA with 3.6-fold higher affinity, while the Km for serine is 4-fold increased relative to the wild-type SerRS. This indicates the importance of the C-terminal extension in maintaining the overall structure of SerRS.

A new Escherichia coli cell division gene, ftsK

A mutation in a newly discovered Escherichia coli cell division gene, ftsK, causes a temperature-sensitive late-stage block in division but does not affect chromosome replication or segregation. This defect is specifically suppressed by deletion of dacA, coding for the peptidoglycan DD-carboxypeptidase, PBP 5. FtsK is a large polypeptide (147 kDa) consisting of an N-terminal domain with several predicted membrane-spanning regions, a proline-glutamine-rich domain, and a C-terminal domain with a nucleotide-binding consensus sequence. FtsK has extensive sequence identity with a family of proteins from a wide variety of prokaryotes and plasmids. The plasmid proteins are required for intercellular DNA transfer, and one of the bacterial proteins (the SpoIIIE protein of Bacillus subtilis) has also been implicated in intracellular chromosomal DNA transfer.

Postseptational chromosome partitioning in bacteria

Mutations in the spoIIIE gene prevent proper partitioning of one chromosome into the developing prespore during sporulation but have no overt effect on partitioning in vegetatively dividing cells. However, the expression of spoIIIE in vegetative cells and the occurrence of genes closely related to spoIIIE in a range of nonsporulating eubacteria suggested a more general function for the protein. Here we show that SpoIIIE protein is needed for optimal chromosome partitioning in vegetative cells of Bacillus subtilis when the normal tight coordination between septation and nucleoid partitioning is perturbed or when septum positioning is altered. A functional SpoIIIE protein allows cells to recover from a state in which their chromosome has been trapped by a closing septum. By analogy to its function during sporulation, we suggest that SpoIIIE facilitates partitioning by actively translocating the chromosome out of the septum. In addition to enhancing the fidelity of nucleoid partitioning, SpoIIIE also seems to be required for maximal resistance to antibiotics that interfere with DNA metabolism. The results have important implications for our understanding of the functions of genes involved in the primary partitioning machinery in bacteria and of how septum placement is controlled.

A conjugation-like mechanism for prespore chromosome partitioning during sporulation in Bacillus subtilis

Spore formation in Bacillus subtilis begins with an asymmetric cell division that superficially resembles the division of vegetative cells. Mutations in the spoIIIE gene of B. subtilis partially block partitioning of one chromosome into the smaller (prespore) compartment of the sporulating cell. Point mutations that specifically block prespore chromosome partitioning affect a carboxy-terminal domain of SpoIIIE that shows significant sequence similarity to the DNA transfer (Tra) proteins of several conjugative plasmids of Streptomyces. In wild-type sporulating cells, the prespore chromosome passes through an intermediate stage resembling the state in which spoIIIE mutant cells are blocked. The prespore chromosome is then transferred progressively through the newly formed spore septum. We propose that translocation of the prespore chromosome occurs by a mechanism that is functionally related to the conjugative transfer of plasmid DNA.