[44] Secondary ion movements in Halobacterium halobium

Abstract

This chapter describes secondary ion movements and its measurement in Halobacterium halobium. Recording of concentration changes of protons, potassium, and other ions in the suspending basal salt medium can be carried out in a thermostated glass vessel. One of a variety of commercially available pH meters connected to an appropriate recorder can be used, but recordings from the pH electrode should be tested against possible light artifacts and salt errors. For potassium measurements, the highly K + -selective electrode IS 561-K + (Philips) is often used plugged into a PHM 64 research pH meter. The electrode must be shielded against light, and noise and drift problems are greatly reduced if the reference electrode is placed externally in basal salt solution and connected via a basal salt–agar bridge to the reaction vessel. The reaction mixture should be stirred to reduce unstirred layer effects and nonuniform irradiation. Intracellular ion concentrations in collected samples can be determined by atomic absorption spectroscopy or flame photometry. In addition, radioactive isotopes may be used to determine both ion transport processes and the fraction of extracellular space to total pellet volume.