| 1. |
- 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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| 2. |
- 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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| 3. |
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| 4. |
- Forslund, Anna-Lena, 1964-, et al.
(författare)
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The type IV pilin, PilA, is required for full virulence of Francisella tularensis subspecies tularensis
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Annan publikation (populärvet., debatt m.m.)abstract
- Background: All four Francisella tularensis subspecies possess gene clusters with potential to express type IV pili (Tfp). These clusters include putative pilin genes, as well as pilB, pilC and pilQ, required for secretion and assembly of Tfp. A hallmark of Tfp is the ability to retract the pilus upon surface contact, a property mediated by the ATPase PilT. Interestingly, out of the two major human pathogenic subspecies only the highly virulent type A strains have a functional pilT gene.Results: In a previous study, we were able to show that one pilin gene, pilA, was essential for virulence of a type B strain in a mouse infection model. In this work we have examined the role of several pilin genes in the virulence of the pathogenic type A strain SCHU S4. pilA, pilC, pilQ, and pilT were mutated by in-frame deletion mutagenesis. Interestingly, when mice were infected with a mixture of each mutant strain and the wild-type strain, the pilA, pilC and pilQ mutants were out-competed, while the pilT mutant was equally competitive as the wild-type.Conclusions: This suggests that expression and surface localisation of PilA contribute to virulence in the highly virulent type A strain, while PilT was dispensable for virulence in the mouse infection model.
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| 5. |
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| 6. |
- Michell, Stephen, et al.
(författare)
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Extendable Dispatchable Task Communication Mechanisms
- 1999
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Ingår i: IRTAW '99 Proceedings of the ninth international workshop on Real-time AdaPages 54-59. - : Association for Computing Machinery (ACM). - 1581131771 ; , s. 54-59
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The addition of object-oriented features to Ada has left a disconnection between the object-oriented paradigm and the intertask communication and synchronisation paradigms. The lack of extensibility of tasks and protected types as well as the task synchronisation inheritance anomaly has made design of systems that use them with object oriented features more difficult. This paper proposes Ada language changes that would make protected types and tasks partners in object oriented programming and would cure the inheritance anomaly.
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| 7. |
- Salomonsson, Emelie, et al.
(författare)
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Role of type IV pilin encoding genes in virulence of Francisella tularensis subspecies holarctica
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The number of virulence factors identified in Francisella tularensis, the causative agent of tularemia, is so far relatively few. The F. tularensis genome contains some genes with homology to known virulence factors. One of these is the type IV pili system, which is known to have a key role in virulence of other bacterial species. When we compared different F. tularensis subspecies we could identify distinct differences in Type IV pilin genes between the highly virulent type A strains and the less pathogenic type B strains. In this work we addressed the role in virulence of the different pilin genes in a virulent type B strain. Of all the pilin genes only PilA and the pseudopilins FTT1621-1622 were proven to have a role in virulence. In addition we also verified that the gene encoding the PilT ATPase is non-functional due to a non-sense mutation and we also confirmed that the truncated pilT has no role in mouse virulence. Furthermore we also provide evidence that the F. tularensis pilins are posttranslationally modified presumably by glycosylation by a PilO dependent mechanism.
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