| 1. |
- Larsson, Pär, et al.
(författare)
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The complete genome sequence of Francisella tularensis, the causative agent of tularemia
- 2005
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Ingår i: Nature Genetics. - : Springer Science and Business Media LLC. - 1061-4036 .- 1546-1718. ; 37:2, s. 153-159
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Tidskriftsartikel (refereegranskat)abstract
- Francisella tularensis is one of the most infectious human pathogens known. In the past, both the former Soviet Union and the US had programs to develop weapons containing the bacterium. We report the complete genome sequence of a highly virulent isolate of F. tularensis (1,892,819 bp). The sequence uncovers previously uncharacterized genes encoding type IV pili, a surface polysaccharide and iron-acquisition systems. Several virulence-associated genes were located in a putative pathogenicity island, which was duplicated in the genome. More than 10% of the putative coding sequences contained insertion-deletion or substitution mutations and seemed to be deteriorating. The genome is rich in IS elements, including IS630 Tc-1 mariner family transposons, which are not expected in a prokaryote. We used a computational method for predicting metabolic pathways and found an unexpectedly high proportion of disrupted pathways, explaining the fastidious nutritional requirements of the bacterium. The loss of biosynthetic pathways indicates that F. tularensis is an obligate host-dependent bacterium in its natural life cycle. Our results have implications for our understanding of how highly virulent human pathogens evolve and will expedite strategies to combat them.
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| 2. |
- Champion, Mia D, et al.
(författare)
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Comparative genomic characterization of Francisella tularensis strains belonging to low and high virulence subspecies
- 2009
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Ingår i: PLoS pathogens. - : Public Library of Science (PLoS). - 1553-7374. ; 5:5, s. e1000459-
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Tidskriftsartikel (refereegranskat)abstract
- Tularemia is a geographically widespread, severely debilitating, and occasionally lethal disease in humans. It is caused by infection by a gram-negative bacterium, Francisella tularensis. In order to better understand its potency as an etiological agent as well as its potential as a biological weapon, we have completed draft assemblies and report the first complete genomic characterization of five strains belonging to the following different Francisella subspecies (subsp.): the F. tularensis subsp. tularensis FSC033, F. tularensis subsp. holarctica FSC257 and FSC022, and F. tularensis subsp. novicida GA99-3548 and GA99-3549 strains. Here, we report the sequencing of these strains and comparative genomic analysis with recently available public Francisella sequences, including the rare F. tularensis subsp. mediasiatica FSC147 strain isolate from the Central Asian Region. We report evidence for the occurrence of large-scale rearrangement events in strains of the holarctica subspecies, supporting previous proposals that further phylogenetic subdivisions of the Type B clade are likely. We also find a significant enrichment of disrupted or absent ORFs proximal to predicted breakpoints in the FSC022 strain, including a genetic component of the Type I restriction-modification defense system. Many of the pseudogenes identified are also disrupted in the closely related rarely human pathogenic F. tularensis subsp. mediasiatica FSC147 strain, including modulator of drug activity B (mdaB) (FTT0961), which encodes a known NADPH quinone reductase involved in oxidative stress resistance. We have also identified genes exhibiting sequence similarity to effectors of the Type III (T3SS) and components of the Type IV secretion systems (T4SS). One of the genes, msrA2 (FTT1797c), is disrupted in F. tularensis subsp. mediasiatica and has recently been shown to mediate bacterial pathogen survival in host organisms. Our findings suggest that in addition to the duplication of the Francisella Pathogenicity Island, and acquisition of individual loci, adaptation by gene loss in the more recently emerged tularensis, holarctica, and mediasiatica subspecies occurred and was distinct from evolutionary events that differentiated these subspecies, and the novicida subspecies, from a common ancestor. Our findings are applicable to future studies focused on variations in Francisella subspecies pathogenesis, and of broader interest to studies of genomic pathoadaptation in bacteria.
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| 3. |
- Forslund, Anna-Lena, 1964-, et al.
(författare)
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Direct repeat-mediated deletion of a type IV pilin gene results in major virulence attenuation of Francisella tularensis
- 2006
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Ingår i: Molecular Microbiology. - : Wiley-Blackwell. - 0950-382X .- 1365-2958. ; 59:6, s. 1818-1830
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Tidskriftsartikel (refereegranskat)abstract
- Francisella tularensis, the causative agent of tularaemia, is a highly infectious and virulent intracellular pathogen. There are two main human pathogenic subspecies, Francisella tularensis ssp. tularensis (type A), and Francisella tularensis ssp. holarctica (type B). So far, knowledge regarding key virulence determinants is limited but it is clear that intracellular survival and multiplication is one major virulence strategy of Francisella. In addition, genome sequencing has revealed the presence of genes encoding type IV pili (Tfp). One genomic region encoding three proteins with signatures typical for type IV pilins contained two 120 bp direct repeats. Here we establish that repeat-mediated loss of one of the putative pilin genes in a type B strain results in severe virulence attenuation in mice infected by subcutaneous route. Complementation of the mutant by introduction of the pilin gene in cis resulted in complete restoration of virulence. The level of attenuation was similar to that of the live vaccine strain and this strain was also found to lack the pilin gene as result of a similar deletion event mediated by the direct repeats. Presence of the pilin had no major effect on the ability to interact, survive and multiply inside macrophage-like cell lines. Importantly, the pilin-negative strain was impaired in its ability to spread from the initial site of infection to the spleen. Our findings indicate that this putative pilin is critical for Francisella infections that occur via peripheral routes.
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| 4. |
- Garbom, Sara, et al.
(författare)
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Phenotypic characterization of a virulence-associated protein, VagH, of Yersinia pseudotuberculosis reveals a tight link between VagH and the type III secretion system.
- 2007
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Ingår i: Microbiology. - : Society for General Microbiology. - 1350-0872 .- 1465-2080. ; 153:Pt 5, s. 1464-73
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Tidskriftsartikel (refereegranskat)abstract
- Recently, a number of attenuated mutants of Yersinia pseudotuberculosis have been identified using a bioinformatics approach. One of the target genes identified in that study was vagH, which the authors now characterized further. VagH shows homology to HemK of Escherichia coli, possessing methyltransferase activity similar to that of HemK, and targeting release factors 1 and 2. Microarray studies comparing the wild-type and the vagH mutant revealed that the mRNA levels of only a few genes were altered in the mutant. By proteome analysis, expression of the virulence determinant YopD was found to be increased, indicating a possible connection between VagH and the virulence plasmid-encoded type III secretion system (T3SS). Further analysis showed that Yop expression and secretion were repressed in a vagH mutant. This phenotype could be suppressed by trans-complementation with the wild-type vagH gene or by deletion of the negative regulator yopD. Also, in a similar manner to a T3SS-negative mutant, the avirulent vagH mutant was rapidly cleared from Peyer's patches and could not reach the spleen after oral infection of mice. In a manner analogous to that of T3SS mutants, the vagH mutant could not block phagocytosis by macrophages. However, a vagH mutant showed no defects in the T3SS-independent ability to proliferate intracellularly and replicated to levels similar to those of the wild-type in macrophages. In conclusion, the vagH mutant exhibits a virulence phenotype similar to that of a T3SS-negative mutant, indicating a tight link between VagH and type III secretion in Y. pseudotuberculosis.
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| 5. |
- Titball, Richard W, et al.
(författare)
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Biosafety and selectable markers.
- 2007
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Ingår i: Ann N Y Acad Sci. - 0077-8923. ; 1105, s. 405-17
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Tidskriftsartikel (refereegranskat)
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