ATP and Energy Charge as Criteria of Growth and Metabolic Activity of Mollicutes : Application to Spiroplasma citri

Intracellular ATP concentrations and energy charge were monitored during the growth of Spiroplasma citri and related to the number of colony-forming units, to the pH of the medium and to incorporation of radioactive precursors. Of three different methods used for extracting nucleotides trichloroacetic acid, perchloric acid and boiling Tris/H,SO, buffer the trichloroacetic acid treatment was the most effective. During the active growth phase the ATP concentration increased exponentially, in the same way as other growth parameters. However, as soon as the metabolic activity slowed down, there was a rapid drop of ATP concentration and of total adenylate content, which was followed much later by a parallel decrease in the number of colony-forming units. During active growth, energy charge remained at around 0.9 and decreased only slowly during the stationary phase. Incorporation of labelled thymidine or phenylalanine followed a different pattern during the late phase of the culture and gave less information concerning the viability of the organisms.