VirB3-VirB6 and VirB8-VirB11, but not VirB7, are essential for mediating persistence Brucella in the reticuloendothelial system

University of California, Davis, Department of Medical Microbiology and Immunology, Davis, CA, 95616

	Abstract

The Brucella abortus virB locus contains 12 open reading frames, termed virB1 through virB12, which encode a type IV secretion system (T4SS). Polar mutations in the virB locus markedly reduce the ability of B. abortus to survive in cultured macrophages or to persist in organs of mice. While a non-polar deletion of the virB2 gene reduces survival in cultured macrophages and in organs of mice, a non-polar deletion of virB1 only reduces macrophage survival, while virB12 is dispensable for either virulence trait. Here we investigated the role of the remaining genes in the virB locus during macrophage survival and mouse virulence. Mutants carrying non-polar deletions of the virB3, virB4, virB5, virB6, virB7, virB8, virB9, virB10 or virB11 gene were constructed and characterized. All mutations reduced the ability of B. abortus to survive in J774A.1 mouse macrophage-like cells to a degree similar to that caused by a deletion of the entire virB locus. Deletion of virB3, virB4, virB5, virB6, virB8, virB9, virB10 or virB11 markedly reduced the ability of B. abortus to persist in the spleens of mice at eight weeks after infection. Interestingly, deletion of virB7 did not reduce the ability of B. abortus to persist in spleens of mice. We conclude that virB2, virB3, virB4, virB5, virB6, virB8, virB9, virB10 or virB11 are essential for mouse virulence of B. abortus while functions encoded by the virB1, virB7 and virB12 genes are not required for organ persistence in this animal model.