Identification of a Putative Chaperone Involved in Stress Resistance and Virulence in Francisella tularensis

Abstract

Francisella tularensis is a highly infectious bacterium causing the zoonotic disease tularemia. This facultative intracellular bacterium replicates in vivo mainly inside macrophages and therefore has developed strategies to resist this stressful environment. Here, we identified a novel genetic locus that is important for stress resistance and intracellular survival of F. tularensis. In silico and transcriptional analyses suggest that this locus (genes FTL_0200 to FTL_0209 in the live vaccine strain [LVS]) constitutes an operon controlled by the alternative sigma factor σ³². The first gene, FTL_0200, encodes a putative AAA+ ATPase of the MoxR subfamily. Insertion mutagenesis into genes FTL_0200, FTL_0205, and FTL_0206 revealed a role for the locus in both intracellular multiplication and in vivo survival of F. tularensis. Deletion of gene FTL_0200 led to a mutant bacterium with increased vulnerability to various stress conditions, including oxidative and pH stresses. Proteomic analyses revealed a pleiotropic impact of the ΔFTL_0200 deletion, supporting a role as a chaperone for FTL_0200. This is the first report of a role for a MoxR family member in bacterial pathogenesis. This class of proteins is remarkably conserved among pathogenic species and may thus constitute a novel player in bacterial virulence.