The arginine-ornithine transporter, ArgT, plays an essential role in the survival of Brucella in macrophages and mice

Brucella species are facultative intracellular bacterial pathogens that cause the contagious zoonotic disease, brucellosis. Brucella spp. infect a wide range of animals, including livestock, wild animals, and marine mammals. Brucellosis remains endemic to various parts of the world, affecting the economic growth of many countries because of its impact on public health and livestock productivity. There are no human vaccines for brucellosis, and controlling the disease in susceptible animals is crucial for limiting human infections. Although the available live-attenuated vaccines have protective efficacy in animals, they have many disadvantages, including infectivity in humans. Compared with other invasive bacterial pathogens, minimal information is available on the virulence factors of Brucella that enable them to survive in the host. Here, we performed transposon-based random mutagenesis of B. neotomae and identified the arginine/ornithine binding protein, ArgT, as the crucial virulence determinant of Brucella. Deleting ArgT from B. melitensis resulted in its attenuation in macrophages, which was restored upon complementation with an ArgT expression plasmid. We observed that macrophages infected with {Delta}ArgT-Brucella produced elevated levels of NO due to the inability of {Delta}ArgT Brucella to deplete the host intracellular arginine through its importer. Furthermore, defective survival of {Delta}ArgT B. melitensis was observed in the infected mice, which correlated with enhanced NO production in the mice. Our studies revealed that ArgT in Brucella plays a vital role in preventing intracellular killing and contributes to the chronic persistence of Brucella in the host. This study highlights the essential role of arginine in clearing intracellular infections and the subversion of this host defense mechanism by intracellular pathogens for their chronic persistence.