Coordination of Phosphate and Magnesium Metabolism in Bacteria.

The majority of cellular phosphate (PO 4 -3 ; Pi) exists as nucleoside triphosphates, mainly adenosine triphosphate (ATP), and ribosomal RNA (rRNA). ATP and rRNA are also the largest cytoplasmic reservoirs of magnesium (Mg 2+ ), the most abundant divalent cation in living cells. The co-occurrence of these ionic species in the cytoplasm is not coincidental. Decades of work in the Pi and Mg 2+ starvation responses of two model enteric bacteria, Escherichia coli and Salmonella enterica, have led to the realization that the metabolisms of Pi and Mg 2+ are interconnected. Bacteria must acquire these nutrients in a coordinated manner to achieve balanced growth and avoid loss of viability. In this chapter, we will review how bacteria sense and respond to fluctuations in environmental and intracellular Pi and Mg 2+ levels. We will also discuss how these two compounds are functionally linked, and how cells elicit physiological responses to maintain their homeostasis.