Brucella abortus histidine auxotrophs are sensitive to copper
Despite decades of investigation into bacterial pathogens, the conditions met by intracellular bacteria are still unclear. These conditions can include access to nutrients, such as amino acids, and exposure to toxic compounds, like copper. To investigate the ability of Brucella abortus, a facultative intracellular pathogen responsible for a major zoonosis, to cope with copper, we performed a Tn-seq analysis to identify copper-sensitive mutants. Unexpectedly, we realized that classical copper resistance systems (involving CopA and CueO homologs) do not appear to be robustly needed, while histidine and purine biosynthesis pathways are crucial to cope with copper. We show that hisA, hisB, hisC and hisD mutants are auxotrophic for histidine and sensitive to copper. This suggests that the reported attenuation of his mutants in macrophages could be based on auxotrophy or/and copper sensitivity. Therefore, we generated suppressor strains with a restored resistance to copper for hisC, but still auxotrophs for histidine. Our data suggest that this suppression is due to the overproduction of a homolog of OppA, a periplasmic oligopeptide binding protein. Analysis of these suppressors shows that the absence of histidine biosynthesis capacity, and not copper sensitivity, is required for optimal growth of B. abortus in macrophages.