Thermoplasma acidophilum: intracellular pH and potassium concentration.

Thermoplasma acidophilum is a free-living thermophilic mycoplasma. Although the organism lacks a cell wall, it can grow in medium as dilute as 66 mosM. The intracellular K+ concentration can be as low as 17 mM, but varies according to the osmolality of the culture medium. The internal pH can be measured by taking advantage of the fact that T. acidophilum undergoes lysis when the pH is adjusted to neutrality. Thus, by appropriate analysis of titration curves, it is possible to conclude that the internal pH is near 5.5. This result was confirmed by a second type of experiment in which the internal pH was analyzed by rupturing the cells in a French Pressure Cell.