LOVHK regulates the General Stress Response system and virB expression in Brucella abortus

GABRIELA SYCZ; TONG-SEUNG TSENG; MARCUS FREDERICKSON; MARIELA DEL CARMEN CARRICA; WINSLOW BRIGGS; ROBERTO BOGOMOLNI; FERNANDO A. GOLDBAUM; GASTÓN PARIS

Córdoba

Conferencia; 16th International Congress on Photobiology; 2014

16th International Congress on Photobiology

Bacteria can detect and respond to environmental changes through two-component signalling systems (TCS), which consist of a sensor histidine kinase (HK) and its cognate response regulator (RR). The Brucella genome encodes a sensor HK, LOVHK, which has three domains: a LOV (Light-Oxygen-Voltage) N-terminal domain, a PAS domain and finally a C-terminal HK domain which belongs to the HWE family. After exposure to blue light, the LOV domain initiates a self-contained photocycle, which promotes autophosphorylation of the HK domain. This leads to a signal transduction pathway that ends with an increment in Brucella virulence [1]. Using two-hybrid assays and phosphotransfer experiments we identified two RRs as interacting partners for LOVHK: a single domain RR named LovR and PhyR which has two domains. Phosphotransfer assays suggest that LovR is functioning as a phosphate sink for LOVHK, decreasing the phosphorylation level of LOVHK. PhyR is an anti-anti sigma factor which is involved in the General Stress Response (GSR) system characteristic of alphaproteobacteria and recently described in Brucella abortus [2,3]. Using qRT-PCR analysis, we demonstrated that phyR and other genes regulated by the GSR system are down-regulated in the lovhk mutant. We have also confirmed that PhyR protein level is decreased in the lovhk mutant compared to the wt. Expression assays using virB promoter fused to lacZ confirmed that LOVHK regulates virB expression. Light activation of the GSR system and virB expression is still under evaluation. In conclusion, our results suggest that LOVHK activates the GSR system and modulates virB gene expression, modifying the virulence of Brucella. [1] T. E. Swartz et al., Science, 2007, 317, 1090. [2] A. Staron et al., Mol Microbiol, 2010, 78(2), 271. [3] H. S. Kim et al., J Biol Chem, 2013, 288(19), 13906.