LOV Histidine Kinase Modulates the General Stress Response System and Affects the <i>virB</i> Operon Expression in <i>Brucella abortus</i>

<div><p><i>Brucella</i> is the causative agent of the zoonotic disease brucellosis, and its success as an intracellular pathogen relies on its ability to adapt to the harsh environmental conditions that it encounters inside the host. The <i>Brucella</i> genome encodes a sensor histidine kinase containing a LOV domain upstream from the kinase, LOVHK, which plays an important role in light-regulated <i>Brucella</i> virulence. In this report we study the intracellular signaling pathway initiated by the light sensor LOVHK using an integrated biochemical and genetic approach. From results of bacterial two-hybrid assays and phosphotransfer experiments we demonstrate that LOVHK functionally interacts with two response regulators: PhyR and LovR, constituting a functional two-component signal-transduction system. LOVHK contributes to the activation of the General Stress Response (GSR) system in <i>Brucella</i> via PhyR, while LovR is proposed to be a phosphate-sink for LOVHK, decreasing its phosphorylation state. We also show that in the absence of LOVHK the expression of the <i>virB</i> operon is down-regulated. In conclusion, our results suggest that LOVHK positively regulates the GSR system <i>in vivo</i>, and has an effect on the expression of the <i>virB</i> operon. The proposed regulatory network suggests a similar role for LOVHK in other microorganisms.</p>