Light regulates virulence in Brucella abortus by a LOV- Domain Histidine Kinase protein

GASTÓN PARIS; DIEGO J. COMERCI; TREVOR E. SWARTZ; ROBERTO BOGOMOLNI; RODOLFO A. UGALDE; FERNANDO E GOLDBAUM

Bath (UK)

Congreso; European Society for Photobiology 2007; 2007

European Society for Photobiology

Brucella abortus is a facultative intracellular pathogen that causes brucellosis in domestic animals and humans. Brucella invades and replicates inside professional and non-professional phagocytes. Two- sensor/histidine kinase signaling proteins are widely recognized as environmental sensors in bacteria. B. abortus contains a LOV-histidine kinase (LOV-HK) protein. LOV domains which belong to the PAS domain superfamily, are the light sensory modules in plant, fungi and algae photoreceptors. LOV domains bind a single molecule of FMN and undergo a self-contained photocycle that is dependent on the presence of a highly conserved cysteine residue. Upon illumination the reactive cysteine forms a covalent bond between the sulfur and C4a carbon of FMN.  In addition to the LOV domain this protein also has PAS and histidine kinase domains. In order to investigate the in vivo function of the Brucella LOV-HK, the gene was knocked-out and the mutation was checked by PCR. Cell infection assays in J774A.1 macrophages showed that LOV-HK knockout bacteria have an attenuated phenotype as compared with control. A complemented strain expressing the LOV-HK gene in the LOV-HK knockout genetic background was able to rescue the phenotype, showing the same replication rate as wild type. However, the point mutant LOV-HK C69A which cannot under go light induced formation of the covalent adduct between the FMN and the reactive cysteine showed the same infection profile that the LOV-HK knockout strain, indicating that formation of covalent adduct is essential to restore its biological activity. To determine if LOV-HK functions as photoreceptor during host-pathogen interactions, the infection experiment was performed in light vs. dark conditions. Strikingly,  the number of wild type bacteria surviving in the culture kept in the dark was roughly an order of magnitude less than in the light-treated culture and indeed no better than the LOV-HK knockout mutant. Activation of LOV-HK protein by light could be part of an adaptive mechanism present in Brucella that senses its transition from outside the organism and prepares the bacteria for effective infection of a new mammalian host.