Identification of specific environmental signals that trigger the simultaneous expression of vjbR and additional Brucella intracellular survival-related genes

GASTÓN M. AROCENA; ANGELES ZORREGUIETA; RODRIGO SIEIRA

Buenos Aires

Congreso; Brucellosis 2011-International Research Conference-64th Brucellosis Research Conference; 2011

Asociación Argentina de Microbiología

Quorum Sensing (QS) is a widespread cell to cell communication mechanism that participates in the regulation of many bacterial physiological processes. Recently, it was demonstrated that a QS-related regulator named VjbR plays a central role in the pathogenicity of Brucella. VjbR directly regulates the expression of the virB operon, a virulence determinant that is induced shortly after internalization in the host macrophages. Intracellular induction of the virB genes is transient and depends on acidification of the Brucella-containing vacuole. Our aim was to identify a culture condition that mimics the intracellular environment where the virB and other genes are induced in a VjbR-dependent manner. To this end, we first assayed different media for detection of VjbR by Western blot in bacterial cultures. This approach allowed us to find a specific experimental condition that promotes the expression of high amounts of VjbR. It requires the convergence of different signals which involve starvation, a defined metabolic state of the bacterium, and a particular pH value that Brucella necessary has to face during the acidification of the vacuole. In addition, we observed that this condition also triggered the expression of the virB operon and additional genes that participate in the survival of Brucella within the host cell. Analysis of promoter activity suggested that such environmental conditions modulate gene expression at the transcriptional or post-transcptional level, depending on the specific target gene. Taken together, our findings revealed the existence of a regulatory network that controls the expression of important virulence determinants of Brucella. This network is activated in response to specific signals which are similar to those encountered by Brucella within the host cell. The study of variables that govern intracellular survival-related gene regulation will contribute to the understanding of the features of the vacuole that Brucella encounters within the host marchophages.