Bacterial Mg²⁺ homeostasis, transport, and virulence

Organisms must maintain physiological levels of Mg²⁺ because this divalent cation is critical for the stabilization of membranes and ribosomes, for the neutralization of nucleic acids, and as a cofactor in a variety of enzymatic reactions. In this review, we describe the mechanisms that bacteria utilize to sense the levels of Mg²⁺ both outside and inside the cytoplasm. We examine how bacteria achieve Mg²⁺ homeostasis by adjusting the expression and activity of Mg²⁺ transporters and by changing the composition of their cell envelope. We discuss the connections that exist between Mg²⁺ sensing, Mg²⁺ transport, and bacterial virulence. Additionally, we explore the logic behind the fact that bacterial genomes encode multiple Mg²⁺ transporters and distinct sensing systems for cytoplasmic and extracytoplasmic Mg²⁺. These analyses may be applicable to the homeostatic control of other cations.