The two-component system BvrR/BvrS essential for Brucella abortus virulence regulates the expression of outer membrane proteins with counterparts in members of the Rhizobiaceae

摘要

The Brucella BvrR/BvrS two-component regulatory system is homologous to the Chvl/ChvG systems of Sinorhizobium meliloti and Agrobacterium tumefaciens necessary for endosymbiosis and pathogenicity in plants. BvrR/BvrS controls cell invasion and in-tracellular survival. Probing the surface of bvrR and bvrS transpo-son mutants with monoclonal antibodies showed all described major outer membrane proteins (Omps) but Omp25, a protein known to be involved in Brucella virulence. Absence of Omp25 expression was confirmed by two-dimensional electrophoresis of envelope fractions and by gene reporter studies. The electro-phoretic analysis also revealed reduction or absence in the mutants of a second set of protein spots that by matrix-assisted laser desorption ionization MS and peptide mass mapping were identified as a non-previously described Omp (Omp3b). Because bvrR and bvrS mutants are also altered in cell-surface hydrophobicity, permeability, and sensitivity to surface-targeted bactericidal pep-tides, it is proposed that BvrR/BvrS controls cell envelope changes necessary to transit between extracellular and intracellular environments. A genomic search revealed that Omp25 (Omp3a) and Omp3b belong to a family of Omps of plant and animal cell-associated α-Proteobacteria, which includes Rhizobium legumino-sarum RopB and A. tumefaciens AopB. Previous work has shown that RopB is not expressed in bacteroids, that AopB is involved in tumorigenesis, and that dysfunction of A. tumefaciens Chvl/ChvG alters surface properties. It is thus proposed that the BvrR/BvrS and Omp3 homologues of the cell-associated α-Proteobacteria play a role in bacterial surface control and host cell interactions.