Phosphorylation and carbon dioxide fixation in the autotrophic bacterium, Thiobacillus thiooxidans.

Over ten years ago we published a series of papers on the metabolism of Thiobacillsthiooxidakrs, an autotrophic bacterium discovered by Waksman and Joffe (1922), which oxidizes sulfur to sulfuric acid (LePage, 1942; LePage and Umbreit, 1943; O'Kane, 1942; Umbreit, 1947; Umbreit and Anderson, 1942; Umbreit et al., 1942; Vogler, 1942a, b; Vogler et al., 1942; Vogler and Umbreit, 1941, 1942). The conclusions derived from this study were the following: (1) The energy derived from sulfur oxidation is converted into energy of phosphorylation. (2) Carbon dioxide fixation involves the utilization of the energy of phosphorylation. (3) If sulfur is oxidized without carbon dioxide, the energy resulting from this oxidation need not be utilized immediately for carbon dioxide fixation but may be held in the cell for an interval and at some later time may be used for the fixation of carbon dioxide. These conclusions were based upon a study of phosphate exchange and manometric determinations of carbon dioxide fixation. The validity of these conclusions has now been questioned by Baalsrud and Baalsrud (1952) who were unable to find significant phosphate exchange related to sulfur oxidation and carbon dioxide fixation and found no ability to fix carbon dioxide except in the presence of simultaneous oxidation of thiosulfate. These somewhat contradictory results were surprising to us since we had assumed that the phenomena earlier reported were strictly reproducible, that they extended to other strains of autotrophic bacteria, and that the conditions of growth of the culture and those of the metabolic measurements, while they might cause variations in phosphate exchange, etc., would still influence the results in a quantitative more than in a qualitative manner. At this juncture at least two possibilities needed consideration. The first was that we had been entirely misled in the earlier work and that the conclusions we had reached were not valid for even the organism and the conditions studied. The second was that the phenomenon was more restricted than supposed and that it related to cells grown on sulfur, supplied only sulfur as an energy source, and did not apply to the conditions used by Baalsrud and Baalsrud (1952) who not only employed different strains, but used thiosulfate exclusively. One might assume that sulfur and thiosulfate were equivalent, but in our earlier work we had not been able to make much progress in using thiosulfate, and while we had assumed that the same phenomena occurred, this assumption might not be true. While we were not in a good position to undertake an extensive study of the many aspects of this problem, we were able to do some limited experiments bearing on the first possibility. The results of these experiments tend to support the presumption that at least a portion of the earlier conclusions is valid for the organism and conditions employed.