Transcriptional activation of the Brucella abortus virB operon

RODRIGO SIEIRA, DIEGO J. COMERCI Y RODOLFO A. UGALDE.

Carlos Paz, Córdoba, Argentina.

Congreso; XXXVII Reunión Anual de la Sociedad Argentina de Investigación en Bioquímica y Biología Molecular (SAIB); 2001

Brucella spp. are Gram negative, facultative intracellular pathogens that cause brucellosis, a worldwide distributed zoonosis that affects many mammalian species including humans. Recent studies carried out in our laboratory showed that an operon coding for a type IV export apparatus is present in B. abortus and is the major determinant of virulence. These virB genes are essential for the biogenesis of a competitive intracellular replication niche. The intracellular transcription of the virB operon was tested using a transcriptional fusion between the virB promoter and the lacZ gene. After internalization in J774 cells, the activity starts to increase reaching the maximum level at 15 hours p.i. Afterwards the operon turned off, thus indicating that the virB machinery is required during the early steps of infection to redirect the traffic of the Brucella-containing vacuole. In vitro activity experiments showed that the virB promoter is induced at the staitonary phase in rich medium. On the other hand, the induction takes place during the exponential growth phase in minimal medium, thus suggesting that this operon might be controlled by the metabolic status of the bacteriua. The expression level of the VirB2 and VirB7 proteins was analyzed by western in rich medium. The ammount of protein dectected at the stationary phase was higher that during the exponential phase. All these observations suggest that B. abortus senses unknown stimuli to induce the virB expression.