STUDIES ON THE METABOLISM OF THE AUTOTROPHIC BACTERIA : III. THE NATURE OF THE ENERGY STORAGE MATERIAL ACTIVE IN THE CHEMOSYNTHETIC PROCESS

In the autotrophic bacterium, Thiobacillus thiooxidans, the oxidation of sulfur is coupled to transfers of phosphate from the medium to the cells. CO₂ fixation is coupled to transfers of inorganic phosphate from the cells to the medium and is dependent, in the absence of concomitant sulfur oxidation, upon the amount of phosphate previously taken up during sulfur oxidation. The energy reservoir, which is formed by sulfur oxidation in the absence of CO₂ and which can be released for the fixation of CO₂ under conditions which do not permit sulfur oxidation, is a phosphorylated compound and the data suggest that the energy is stored in the cell as phosphate bond energy. It is possible to oxidize sulfur at a constant rate for hours in the absence of CO₂. The phosphate energy formed during this process is probably released by cell phosphotases. It is possible to inhibit these phosphotases by means of inorganic phosphate and thus to inhibit sulfur oxidation in the absence of CO₂. In the presence of CO₂, where alternative uses for the phosphate energy are available, the inhibition is relieved. Sulfur oxidation (energy input) is coupled, not to CO₂ fixation, but to phosphate esterification. CO₂ fixation (energy utilization) is coupled with phosphate release.