Type IV secretion systems (T4SS) are multicomponent machineries involved in the translocation of effector molecules across the bacterial cell envelope. The virB operon of Brucella abortus codes for a T4SS that is essential for virulence and intracellular multiplication of the bacterium in the host. Previous studies showed that the virB operon of B. abortus is tightly regulated within the host cells. In order to identify factors implicated in the control of virB expression, we searched for proteins of Brucella that directly bind to the virB promoter (P virB ). Using different procedures, we isolated a 27-kDa protein that binds specifically to P virB . This protein was identified as HutC, the transcriptional repressor of the histidine utilization (hut) genes. Analyses of virB and hut promoter activity revealed that HutC exerts two different roles: it acts as a coactivator of transcription of the virB operon, whereas it represses the hut genes. Such activities were observed both intracellularly and in bacteria incubated under conditions that resemble the intracellular environment. Electrophoresis mobility shift assays (EMSA) and DNase I footprinting experiments revealed the structure, affinity, and localization of the HutC-binding sites and supported the regulatory role of HutC in both hut and virB promoters. Taken together, these results indicate that Brucella coopted the function of HutC to coordinate the Hut pathway with transcriptional regulation of the virB genes, probably as a way to sense its own metabolic state and develop adaptive responses to overcome intracellular host defenses.Type IV secretion systems (T4SS) are multicomponent machineries central to the pathogenesis of many bacterial genera (e.g., Brucella, Agrobacterium, Helicobacter, Legionella, and Bordetella) (4). T4SS function comprises recognition and translocation of specific substrates across the bacterial cell envelope. The nature of the translocated substrates varies from proteins to DNA-protein complexes. In addition to the wellstudied Agrobacterium transferred DNA (T-DNA) and Bordetella pertussis toxin, several translocated effectors have been identified for Helicobacter, Legionella, and Brucella (7). In every case, the translocated molecules alter cellular processes in such a way that allows the pathogen to overcome host defenses.Brucella is a gram-negative bacterium that causes brucellosis, a worldwide zoonosis that affects domestic mammals. Different Brucella species vary in their host preferences. Brucella abortus, Brucella suis, and Brucella melitensis infect cattle, pigs, and goats, respectively, but also infect humans. In animals, the symptoms of the disease are sterility in males and abortion in pregnant females (6). In humans, brucellosis causes undulant fever during the acute phase and, if it reaches chronicity, can lead to endocarditis, osteoarthritis, and neurological damage.Brucella is an intracellular parasite that persists and replicates within host macrophages. After internalization, the bacterium actively controls the matur...
dBrucella is responsible for brucellosis, one of the most common zoonoses worldwide that causes important economic losses in several countries. Increasing evidence indicates that adhesion of Brucella spp. to host cells is an important step to establish infection. We have previously shown that the BmaC unipolar monomeric autotransporter mediates the binding of Brucella suis to host cells through cell-associated fibronectin. Our genome analysis shows that the B. suis genome encodes several additional potential adhesins. In this work, we characterized a predicted trimeric autotransporter that we named BtaE. By expressing btaE in a nonadherent Escherichia coli strain and by phenotypic characterization of a B. suis ⌬btaE mutant, we showed that BtaE is involved in the binding of B. suis to hyaluronic acid. The B. suis ⌬btaE mutant exhibited a reduction in the adhesion to HeLa and A549 epithelial cells compared with the wild-type strain, and it was outcompeted by the wild-type strain in the binding to HeLa cells. The knockout btaE mutant showed an attenuated phenotype in the mouse model, indicating that BtaE is required for full virulence. BtaE was immunodetected on the bacterial surface at one cell pole. Using old and new pole markers, we observed that both the BmaC and BtaE adhesins are consistently associated with the new cell pole, suggesting that, in Brucella, the new pole is functionally differentiated for adhesion. This is consistent with the inherent polarization of this bacterium, and its role in the invasion process.
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