A homologue of the <i>Agrobacterium tumefaciens</i> VirB and <i>Bordetella pertussis</i> Ptl type IV secretion systems is essential for intracellular survival of <i>Brucella suis</i>

TLDR

A 11,860‑bp type IV secretion system homologous to Agrobacterium VirB and Bordetella Ptl was identified as essential for Brucella suis intracellular survival. The virB locus encodes 12 proteins homologous to the VirB system; mutants in virB5, virB9, or virB10 are highly attenuated in macrophages, and virulence is restored by complementation, confirming the locus is essential for intracellular survival and multiplication of B.

Abstract

Analysis of a Tn blaM mutant of Brucella suis 1330, identified as being unable to multiply in Hela cells, allowed us to identify a 11 860 bp region of the B. suis genome encoding a type IV secretion system, homologous to the VirB system of Agrobacterium tumefaciens and the Ptl system of Bordetella pertussis . DNA sequence revealed 12 open reading frames (ORFs) encoding homologues of the 11 VirB proteins present in the pTi plasmid of Agrobacterium with a similar genetic organization, and a twelfth ORF encoding a putative lipoprotein, homologous to a protein involved in mating pair formation during bacterial conjugation and to adhesins used by Pseudomonas species to bind to plant roots. Phylogenetic trees based on the sequences of VirB4 and VirB9 protein homologues suggest that evolution of the systems from DNA transfer towards protein secretion did not stem from a single event but that the protein secretion systems have evolved independently. Four independent mutants in virB5 , virB9 or virB10 were highly attenuated in an in vitro infection model with human macrophages. The virulence was restored by complementation with a plasmid containing the full virB region. The virB region appears to be essential for the intracellular survival and multiplication of B. suis .