Abstract
Copper is a heavy metal that plays an essential role as a co-factor for several proteins involved in biochemical processes. However, it can become toxic to bacteria when its concentration increases. To avoid damage, the bacteria have to put in place mechanisms to control the concentration of copper and to allow the homeostasis of the metal. Currently, the mechanisms used by Brucella abortus to maintaincopper homeostasis are unknown. In our laboratory, different mutants deleted for several genes of the histidine biosynthesis pathway showed lower replication in two infection models: HeLa cells and RAW 264.7 macrophages. Histidine is an amino acid that has the ability to coordinate different metal ions. In the present work, we investigated the impact of the deletion of histidine synthesis genes on copper homeostasis in B. abortus. First of all, a bioinformatics analysis was carried out to identify histidine-enriched proteins in the bacterium, and confirmed the link between this amino acid and metals. Secondly, we demonstrated that his mutants showed lower growth when copper was present in the medium, illustrating a sensitivity to copper. In addition, we were able to isolate suppressors with various mutations in the opp operon, suggesting that this could be a way for the bacteria to escape the toxicity of copper. It was also found that B. abortus does not show this sensitivity when actors classically described as involved in copper resistance are deleted. In conclusion, our results suggest that B. abortus would use histidine as the first line of defense against copper toxicity rather than the systems usually described.
