Potassium transporters and channels in bacterial survival

Potassium ion homeostasis is essential for bacterial survival, playing roles in osmoregulation, pH homeostasis, regulation of protein synthesis, enzyme activation, membrane potential adjustment and electrical signaling. To accomplish such diverse physiological tasks, it is not surprising that a single bacterium typically encodes several potassium uptake and release systems. To understand the role each individual protein fulfills and how these proteins work in concert, it is important to identify the molecular details of their function. One needs to understand whether the systems transport ions actively or passively, and what mechanisms or ligands lead to the activation or inactivation of individual systems. Combining mechanistic information with knowledge about the physiology under different stress situations, such as osmostress, pH stress or nutrient limitation, one can identify the task of each system and deduce how they are coordinated with each other. I will discuss the roles of the three major bacterial potassium uptake systems, the ion channels TrkAH and KtrAB, the proton-coupled potassium transporter KUP and the potassium pump KdpFABC, based on their molecular structure and function. In particular, I will highlight the regulation of the individual systems by phospholipids and nucleotides, nucleotide second messengers and phosphorylation, which links back to bacterial physiology.