Direct repeat-mediated deletion of a type IV pilin gene results in major virulence attenuation of Francisella tularensis.
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.
Forslund
Anna-Lena
AL
Department of Medical Countermeasures, Division of NBC-Defence, Swedish Defence Research Agency, Umea.
Kuoppa
Kerstin
K
Svensson
Kerstin
K
Salomonsson
Emelie
E
Johansson
Anders
A
Byström
Mona
M
Oyston
Petra C F
PC
Michell
Stephen L
SL
Titball
Richard W
RW
Noppa
Laila
L
Frithz-Lindsten
Elisabet
E
Forsman
Mats
M
Forsberg
Ake
A
D000818:Animals; D001422:Bacterial Adhesion / Q000235:genetics*; D001483:Base Sequence; D002478:Cells, Cultured; D005260:Female; D036781:Fimbriae Proteins / Q000235:genetics*; D005604:Francisella tularensis / Q000235:genetics / Q000472:pathogenicity*; D017353:Gene Deletion; D005798:Genes, Bacterial; D006801:Humans; D051379:Mice; D008810:Mice, Inbred C57BL; D008969:Molecular Sequence Data; D005810:Multigene Family; D012091:Repetitive Sequences, Nucleic Acid / Q000235:genetics*; D014158:Transcription, Genetic; D014406:Tularemia / Q000382:microbiology*; D014774:Virulence / Q000235:genetics
D036781:Fimbriae Proteins