The biosynthetic pathway of ubiquinone contributes to pathogenicity ofFrancisella

AbstractFrancisella tularensisis the causative agent of tularemia. Because of its extreme infectivity and high mortality rate, this pathogen was classified as a biothreat agent.Francisellaspp are strict aerobe and ubiquinone (UQ) has been previously identified in these bacteria. While the UQ biosynthetic pathways were extensively studied inEscherichia coliallowing the identification of fifteen Ubi-proteins to date, little is known aboutFrancisellaspp. In this study, and usingFrancisella novicidaas a surrogate organism, we first identified UQ8as the major quinone found in the membranes of this bacterium. Then, we characterized the UQ biosynthetic pathway inF. novicidausing a combination of bioinformatics, genetics and biochemical approaches. Our analysis disclosed the presence inFrancisellaof ten putative Ubi-proteins and we confirmed eight of them by heterologous complementation inE. coli. The UQ biosynthetic pathways fromF. novicidaandE. colishare a similar pattern. However, differences were highlighted: the decarboxylase remains unidentified inFrancisellaspp and homologs of the Ubi-proteins involved in the O2-independent UQ pathway are not present. This is in agreement with the strictly aerobic niche of this bacterium. Then,viatwo approaches, i.e. the use of an inhibitor (3-amino-4-hydroxybenzoic acid) and a transposon mutant, which both strongly impair the synthesis of UQ, we demonstrated that UQ is essential for the growth ofF. novicidain a respiratory medium and contributes to its pathogenicity inGalleria mellonellaused as an alternative animal model.ImportanceFrancisella tularensisis the causative bacterium of tularemia and is classified as a biothreat agent. Using multidisciplinary approaches, we investigated the ubiquinone (UQ) biosynthetic pathway that operates inF. novicidaused as a surrogate. We showed that UQ8is the major quinone identified in the membranes ofFrancisella novicida. We identified a new competitive inhibitor, which strongly decreased the biosynthesis of UQ. Our demonstration of the crucial role of UQ for the respiratory metabolism ofF. novicidaand for the involving in its pathogenicity in theGalleria mellonellamodel should stimulate the search for selective inhibitors of bacterial UQ biosynthesis.