October 2008

Document Type


Degree Name



Dept. of Molecular Microbiology and Immunology


Oregon Health & Science University


Francisella tularensis is a highly infectious bacterium whose mechanisms of pathogenesis are just beginning to be defined. Until recently, there were a very limited number of procedures available for studying F. tularensis; hence, only a handful of virulence factors and targets for vaccine development had been identified. Additionally, the process of Francisella entry is poorly understood. The work presented in this thesis addresses these issues with the development of a transposon mutagenesis technique and its application for the discovery of several novel virulence factors in F. tularensis ssp. novicida. Subsequent studies demonstrated that immunization with mutant derivatives of four of these virulence factors provided protection against challenge with high doses of wild-type bacteria in a mouse model, thus showing promise as suitable candidates for vaccine development. One of the transposon insertions disrupted an uncharacterized hypothetical gene. Sequence analysis revealed the presence of seven tandem repeat motifs in this gene in subspecies novicida that are present in one or two copies in other F. tularensis homologs. Expression and characterization of one of the repeat units showed that it is a stably folded domain capable of forming oligomers. Further studies suggest that this motif may have a specific role in F. tularensis entry, as it binds host surface factors associated with the Ecadherin complex and shares sequence and structural homology with repeat domains of a Staphylococcus aureus protein that is important for adherence and entry into host cells. Together, the experiments described in this thesis provide information about the virulence strategies of Francisella and will facilitate future studies regarding vaccine development and elucidating the molecular mechanisms of Francisella pathogenesis.




School of Medicine



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