STUDIES ON THE METABOLISM OF AUTOTROPHIC BACTERIA : II. THE NATURE OF THE CHEMOSYNTHETIC REACTION.

In a study of chemosynthesis (the fixation of CO(2) by autotrophic bacteria in the dark) in Thiobacillus thiooxidans, the data obtained support the following conclusions: 1. CO(2) can be fixed by "resting cells" of Thiobacillus thiooxidans; the fixation is not "growth bound." 2. The physiological condition of the cell is of considerable importance in determining CO(2) fixation. 3. CO(2) fixation can occur in the absence of oxidizable sulfur in "young" cells. The extent of this fixation appears to be dependent upon the pCO(2). 4. CO(2) fixation can also occur under anaerobic conditions and the presence of sulfur does not influence such fixation. 5. However, in the CO(2) fixation by cells in the absence of sulfur, only a limited amount of CO(2) can be fixed. This amount is approximately 40 microl. CO(2) per 100 micrograms bacterial nitrogen. After a culture has utilized this amount of CO(2) it no longer has the ability to fix CO(2) but releases it during its respiration. 6. Relatively short periods of sulfur oxidation can restore the ability of cells to fix CO(2) under conditions where sulfur oxidation is prevented. 7. It is possible to oxidize sulfur in the absence of CO(2) and to store the energy thus formed within the cell. It is then possible to use this energy at a later time for the fixation of CO(2) in the entire absence of sulfur oxidation. 8. Cultures of Thiobacillus thiooxidans respiring on sulfur utilize CO(2) in a reaction which proceeds to a zero concentration of CO(2) in the atmosphere. 9. CO(2) may act as an oxidizing agent for sulfur. 10. Hydrogen is not utilized by the organism. 11. It is possible to selectively inhibit sulfur oxidation and CO(2) fixation.