from Ignacio López-Goñi writing in Brucella: Molecular Microbiology and Genomics:
Recent results from proteomic and transcriptomic analyses show that the two component system BvrR/BvrS of Brucella is an global regulator capable of interacting with other regulators, by controlling the synthesis of components of the cell envelope and outer membrane, metabolism of carbon and nitrogen, and of other genes related to the virulence of the bacteria. In this way, the bacteria may sense when they enter a eukaryotic host cell and thus control the expression of a set of genes which allows them to develop during this intracellular phase of their life cycle.
Further reading: Brucella: Molecular Microbiology and Genomics