Functional Diversity of Bacterial Strategies to Cope With Metal Toxicity

Bacterial evolution drove the emergence of various specific and aspecific strategies to cope with hostile environments. Several transition metals (TMs) such as copper, zinc, iron, manganese, and cobalt are essential for most living organisms owing to their implication in a large number of cellular processes. Yet, they turn toxic when their cellular concentration exceeds a specific threshold. It is therefore crucial to maintain an adequate metal homeostasis to ensure a good fitness. In this chapter, we reviewed the main defense mechanisms described in the literature in the context of bacterial exposure to toxic concentrations of TMs. On the one hand, we considered metal dedicated systems that are engaged upon metal stress in distinct bacterial compartments relative to the metal species, its localization, and its cellular targets. On the other, metal resistance was addressed in the context of metabolic and developmental changes at both cellular and population levels. Finally, a case study was devoted to the original bimodal response of the aquatic alphaproteobacterium Caulobacter crescentus to copper stress, illustrating how phenotypic diversity can increase bacterial ability to adapt to changing environments.