An RpoH-Like Heat Shock Sigma Factor Is Involved in Stress Response and Virulence inBrucella melitensis16M

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Abstract
B. melitensis16M genome analysis revealed the presence of six putative sigma factor-encoding genes:rpoD,rpoH1,rpoH2,rpoE1,rpoE2, andrpoN. We mutated all these genes exceptrpoD. Phenotypic analysis of the mutants reveals that a strain carrying anrpoH2null mutation (ΔrpoH2) is impaired for growth at 21 and 42°C and shows increased sensitivity to hydrogen peroxide. Compared to the wild-type strain, the ΔrpoH2mutant is attenuated in all virulence models tested. Three other null mutants (ΔrpoH1, ΔrpoE1, and ΔrpoE2mutants) are also defective for survival in mice at 4 weeks postinfection. We also demonstrated thatrpoH2deletion strongly reduces the expression of two major virulence factors inB. melitensis, the type IV secretion system and the flagellum.