Sulphur metabolism in Thiorhodaceae. II. stoichiometric relationship of CO2 fixation to oxidation of hydrogen sulphide and intracellular sulphur inChromatium okenii

Abstract

Stoichiometry of sulphide and intracellular sulphur oxidation in connection with CO2 fixation was studied inChromatium okenii. The equipment used was a special stirred cuvette with a rapid-sampling arrangement, which allowed short-time experiments with illuminated bacterial suspensions under anaerobic conditions. Turnover of the sulphur compounds is controlled by a linear CO2 fixation rate which amounts to 0.069µmoles of CO2/min mg of cell protein at light saturation. Van Niel's equations for bacterial photosynthesis could be confirmed for short periods under the condition that sulphate is produced during increase of intracellular sulphur; i.e., oxidation of sulphide and of intracellular sulphur do not occur consecutively but simultaneously. The full oxidation rate of intracellular sulphur starts after complete consumption of sulphide. The time during which sulphide is oxidized to intracellular sulphur amounts to 1/3–1/4 of the time necessary for the complete quantitative oxidation of the sulphide to sulphate.