A quorum-sensing regulator controls expression of both the type IV secretion system and the flagellar apparatus of Brucella melitensis

Abstract

SummaryBoth a type IV secretion system and a flagellum have been described in Brucella melitensis . These two multimolecular surface appendages share several features. Their expression in bacteriological medium is growth curve dependent, both are induced intracellularly and are required for full virulence in a mouse model of infection. Here we report the identification of VjbR, a quorum sensing-related transcriptional regulator. A vjbR mutant has a downregulated expression of both virB operon and flagellar genes either during vegetative growth or during intracellular infection. In a cellular model, the vacuoles containing the vjbR mutant or a virB mutant are decorated with the same markers at similar times post infection. The vjbR mutant is also strongly attenuated in a mouse model of infection. As C 12 -homoserine lactone pheromone is known to be involved in virB repression, we postulated that VjbR is mediating this effect. In agreement with this hypothesis, we observed that, as virB operon, flagellar genes are controlled by the pheromone. All together these data support a model in which VjbR acts as a major regulator of virulence factors in Brucella .

Regulation of Type IV Secretion Apparatus Genes during Ehrlichia chaffeensis Intracellular Development by a Previously Unidentified Protein

“…The stringent response mediator Rsh is required for virB expression, suggesting that a nutrient-poor intracellular environment triggers Brucella melitensis virB expression (11). On the other hand, in B. melitensis, a quorumsensing pheromone downregulates virB transcription (9,28). However, an ecxR homolog has not been detected in Brucella, and genes encoding the RelA/SpoT homologs or genes required for biosynthesis of a quorum-sensing pheromone have not been found in the E. chaffeensis genome.…”

“…In L. pneumophila, the two-component PmrB/ PmrA (35) and CpxA/CpxR (13) systems regulate the expression of the icm/dot T4S system. VjbR, a quorum-sensing regulator (9), Rsh, a RelA/SpoT stringent response protein homolog (11), and integration host factor (26) are involved in regulation of the virBD T4S system of Brucella sp. The expression of virBD genes is also regulated during A. phagocytophilum growth in human peripheral blood neutrophils (21).…”

Future research trends in the major chemical language of bacteria

“…Brucella melitensis, which does not contain a luxI homolog but, however, appears to produce AHLs, contains two unpaired LuxR proteins. These are called VjbR and BlxR and have been functionally characterized (Delrue et al, 2005;Rambow-Larsen et al, 2008).…”

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

“…We tested the ability of mutants to invade and survive within J774 macrophages and epithelial (HeLa) cells, using a previously described protocol (9), with 10 5 cells/well. A ⌬vjbR mutant was used as a positive control for attenuation (1). The CFU were counted after 48 h of infection.…”

“…Cellular infections were performed twice in triplicate, with a multiplicity of infection of 300 bacteria per cell. The ⌬vjbR mutant was used as a positive control for attenuation in the cellular models (1).…”