Potential Source of Francisella tularensis Live Vaccine Strain Attenuation Determined by Genome Comparison

Abstract

Francisella tularensis is a bacterial pathogen that causes the zoonotic disease tularemia and is important to biodefense. Currently, the only vaccine known to confer protection against tularemia is a specific live vaccine strain (designated LVS) derived from a virulent isolate of Francisella tularensis subsp. holarctica. The origin and source of attenuation of this strain are not known. To assist with the design of a defined live vaccine strain, we sought to determine the genetic basis of the attenuation of LVS. This analysis relied primarily on the comparison between the genome of LVS and Francisella tularensis holarctica strain FSC200, which differ by only 0.08% of their nucleotide sequences. Under the assumption that the attenuation was due to a loss of function(s), only coding regions were examined in this comparison. To complement this analysis, the coding regions of two slightly more distantly related Francisella tularensis strains were also compared against the LVS coding regions. Thirty-five genes show unique sequence variations predicted to alter the protein sequence in LVS compared to the other Francisella tularensis strains. Due to these polymorphisms, the functions of 15 of these genes are very likely lost or impaired. Seven of these genes were demonstrated to be under stronger selective constraints, suggesting that they are the most probable to be the source of LVS attenuation and useful for a newly defined vaccine.

An intracellularly inducible gene involved in virulence and polyphosphate production in Francisella

“…The same gene was identified during a genome comparison study as a potential cause of attenuation of the LVS strain (Rohmer et al, 2006), as it is a pseudogene in LVS but was intact in 15 further strains examined. The locus appeared to be under strong purifying selection, indicating that its product plays an important role in bacterial survival or fitness (Rohmer et al, 2006). The putative glycosyltransferase is predicted to be involved in cell wall biogenesis or LPS biosynthesis.…”

RespiratoryFrancisella tularensisLive Vaccine Strain Infection Induces Th17 Cells and Prostaglandin E2, Which Inhibits Generation of Gamma Interferon-Positive T Cells

“…(All references to F. tularensis are to LVS unless otherwise noted.) Genomic analysis demonstrates that there is a high level of conservation on the genetic level between F. tularensis LVS and both type A and type B strains, though there are differences (34). Previous studies suggest a difference in the innate immune response to F. tularensis between the intradermal and intranasal inoculation routes (2).…”

Characterization of the Francisella tularensis subsp. novicida type IV pilus

“…As mentioned above, the F. tularensis subsp. novicida genome contains genes with homology to Tfp biogenesis genes (Rohmer et al, 2006). Tfp are predicted to be assembled by a complex that includes the cytoplasmic ATPase PilF, the inner-membrane protein PilG, and the outer membrane secretin PilQ (Burrows, 2005).…”

“…holarctica and subsp. tularensis (Larsson et al, 2005;Petrosino et al, 2006;Rohmer et al, 2006).The ability of F. tularensis to survive and replicate within macrophages has been linked to its virulence (Anthony et al, 1991a), and inactivation of genes necessary for this ability leads to attenuation in mice (Abd et al, 2003;Baron & Nano, 1998; Golovliov et al, 2003a, b;Gray et al, 2002;Lauriano et al, 2004). The global regulator MglA controls transcription of a cluster of genes within the Francisella pathogenicity island (FPI) that are required for intramacrophage survival and growth (Brotcke et al, 2006;Lauriano et al, 2004;Nano et al, 2004 replication.…”