Intracellular pH regulation in bacterial cells

Regulation of cytoplasmic pH is a necessity for every living cell. The proton more than any other ion is involved in almost every physicochemical and biochemical reaction. Bacteria and other microorganisms face challenges that are not experienced by most cells in higher animals. Thus, the proton concentration of their extracellular environments range between pH 1 at the acidic sulfur springs to pH 11 at some soda lakes. Owing to biological activity marked fluctuations of pH values (up to three pH units) occur in many aquatic systems within a diurnal cycle. The extracellular protons are in direct contact with the bacterial outer membrane along with the periplasmic space and cytoplasmic membrane as the cell wall excludes only molecules of molecular weight above 1000. It is evident that the knowledge of pH_i(intracellular pH) and its regulation bears on many aspects of prokaryotic cell physiology including the evaluation of ΔpH which is required for the calculation of the Δμ_H⁺. With this recognition in mind, development and application of methods for determination of pHi in bacteria have been undertaken. This chapter discusses basic principles and some of the specific probes used in bacteria.