Molecular aspects of bacterial pH sensing and homeostasis

In this Review, Krulwich, Sachs and Padan describe how the evolution of diverse mechanisms for pH sensing and homeostasis has enabled bacteria to survive sudden changes in external pH and to grow in environments with external pH values that would otherwise be toxic. Diverse mechanisms for pH sensing and cytoplasmic pH homeostasis enable most bacteria to tolerate or grow at external pH values that are outside the cytoplasmic pH range they must maintain for growth. The most extreme cases are exemplified by the extremophiles that inhabit environments with a pH of below 3 or above 11. Here, we describe how recent insights into the structure and function of key molecules and their regulators reveal novel strategies of bacterial pH homeostasis. These insights may help us to target certain pathogens more accurately and to harness the capacities of environmental bacteria more efficiently.