The B rucella suis I bp A heat‐shock chaperone is not required for virulence or for expression of the V ir B type IV secretion system V ir B 8 protein

Brucella suis , facultative intracellular bacterial pathogen of mammals, and A grobacterium tumefaciens , a plant pathogen, both use a V ir B type IV secretion system ( T 4 SS ) to translocate effector molecules into host cells. HspL, an α‐crystalline‐type small heat‐shock protein, acts as a chaperone for the A grobacterium V ir B 8 protein, an essential component of the V ir B system. An A grobacterium mutant lacking hsp L is attenuated due to a misfunctional T 4 SS . We have investigated whether I bp A ( BRA 0051), the B rucella H sp L homologue, plays a similar role. Unlike H sp L , I bp A does not interact with V ir B 8, and an I bp A mutant shows full virulence and no defect in V ir B expression. These data show that the B rucella α‐crystalline‐type small heat‐shock protein I bp A is not required for B rucella virulence. Significance and Impact of Study Many bacteria use t ype IV secretion systems ( T 4 SS ), multi‐protein machines, to translocate DNA and protein substrates across their envelope. Understanding how T 4 SS function is important as they play major roles in the spread of plasmids carrying antibiotic resistance and in pathogenicity. In the plant pathogen A grobacterium tumefaciens , H sp L , an α‐crystalline‐type small heat‐shock protein, acts as a chaperone for the essential type IV secretion system component V ir B 8. Here, we show that this is not the case for all T 4 SS ; in the zoonotic pathogen B rucella suis , I bp A , the protein most related to H sp L , does not play this role.