The type IV pilin, PilA, is required for full virulence of Francisella tularensis subspecies tularensis.
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 Tfp 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.
Forslund
Anna-Lena
AL
CBRN Defence and Security, FOI Swedish Defence Research Agency, 901 82 Umeå, Sweden.
Salomonsson
Emelie Näslund
EN
Golovliov
Igor
I
Kuoppa
Kerstin
K
Michell
Stephen
S
Titball
Richard
R
Oyston
Petra
P
Noppa
Laila
L
Sjöstedt
Anders
A
Forsberg
Ake
A
D000818:Animals; D005260:Female; D036781:Fimbriae Proteins / Q000235:genetics / Q000378:metabolism*; D005604:Francisella tularensis / Q000235:genetics / Q000378:metabolism* / Q000472:pathogenicity*; D006801:Humans; D051379:Mice; D008810:Mice, Inbred C57BL; D009154:Mutation; D011897:Random Allocation; D014774:Virulence; D037521:Virulence Factors / Q000235:genetics / Q000378:metabolism*
C553424:PilA protein, Francisella tularensis; D037521:Virulence Factors; D036781:Fimbriae Proteins
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