A Coxiella burnetii gene encodes a sensor-like protein

Cytolocalization of the PhoP response regulator in Salmonella enterica: modulation by extracellular Mg2+ and by the SCV environment

The PhoP/PhoQ two-component system plays an essential role regulating numerous virulence phenotypes in Salmonella enterica. Previous work showed that PhoQ, the sensor protein, switches between the kinase- and the phosphatase-dominant state in response to environmental Mg2+ availability. This switch defines the PhoP phosphorylation status and, as a result, the transcriptional activity of this regulator. In this work, using the FlAsH labelling technique, we examine PhoP cytolocalization in response to extracellular Mg2+ limitation in vitro and to the Salmonella-containing vacuole (SCV) environment in macrophage cells. We demonstrate that in these PhoP/PhoQ-inducing environments PhoP displays preferential localization to one cell pole, while being homogeneously distributed in the bacterial cytoplasm in repressing conditions. Polar localization is lost in the absence of PhoQ or when a non-phosphorylatable PhoP(D52A) mutant is expressed. However, when PhoP transcriptional activation is achieved in a Mg2+- and PhoQ-independent manner, PhoP regains asymmetric polar localization. In addition, we show that, in the analysed conditions, PhoQ cellular distribution does not parallel PhoP location pattern. These findings reveal that PhoP cellular location is dynamic and conditioned by its environmentally defined transcriptional status, showing a new insight in the PhoP/PhoQ system mechanism.

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.

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.

Physical and genetic map of the obligate intracellular bacterium Coxiella burnetii

Pulsed-field gel electrophoresis and PCR techniques have been used to construct a NotI macrorestriction map of the obligate intracellular bacterium Coxiella burnetii Nine Mile. The size of the chromosome has been determined to be 2,103 kb comprising 29 NotI restriction fragments. The average resolution is 72.5 kb, or about 3. 5% of the genome. Experimental data support the presence of a linear chromosome. Published genes were localized on the physical map by Southern hybridization. One gene, recognized as transposable element, was found to be present in at least nine sites evenly distributed over the whole chromosome. There is only one copy of a 16S rRNA gene. The putative oriC has been located on a 27.5-kb NotI fragment. Gene organization upstream the oriC is almost identical to that of Pseudomonas putida and Bacillus subtilis, whereas gene organization downstream the oriC seems to be unique among bacteria. The physical map will be helpful in investigations of the great heterogeneity in restriction fragment length polymorphism patterns of different isolates and the great variation in genome size. The genetic map will help to determine whether gene order in different isolates is conserved.

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.

Relationship between pathogenicity of Coxiella burnetii isolates and gene sequences of the macrophage infectivity potentiator (Cbmip) and sensor-like protein (qrsA)

Coxiella burnetii, the Q fever agent, is an obligate intracellular bacterium and survival in phagolysosomes is an important virulence factor. The present study was performed to determine the relationship between its pathogenicity and genes related to its survival in macrophages, i.e. macrophage infectivity potentiator and Q fever agent regulatory sensor-like protein. The sequence similarity was more than 99% among Japanese, European and American strains, and no relationship was found between pathogenicity in guinea pigs and these genes.

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.