UTILISATION OF MOLECULAR HYDROGEN BY CHLOROBIUM THIOSULFATOPHILUM - GROWTH AND CO2-FIXATION

1. All hydrogenase-positive Chlorobium-strains (12 out of 17 strains tested) can grow to some extent with cysteine as a sulfur source, when molecular hydrogen is electron donor. An assimilatory sulfate reduction does not exist. Methionine, cystine, cysteic acid, thioglycolate, thioacetamide, and sulfite in the concentrations tested can not be utilized as a source of cell sulfur. 2. 35S-cysteine is taken up by the cells during growth with hydrogen, and the 35S-label is found in methionine; both these labeled amino acids were shown to occur in the cell protein. The limited growth observed with hydrogen and cysteine may be due to the possibility that not all sulfur compounds of the Chlorobium cells can be built up from cysteine. Free sulfide, normally used as sulfur source, is not formed from cysteine as was shown by CO2-fixation experiments with cysteine. 3. If sulfide or thiosulfate is present in addition to hydrogen, both hydrogen donors are used simultaneously for CO2-fixation. In batch culture about 50% of the CO2 assimilated is reduced with hydrogen; in continous culture the portion of CO2 reduced by hydrogen could be increased to about 90% of total fixation. 4. At low light intensity the rates of CO2-fixation in the presence of hydrogen or thiosulfate are equal. Light saturation of CO2-fixation with hydrogen is reached at about 100-150 lux whereas CO2-fixation with thiosulfate becomes saturated at about 700 lux. At high light intensities this feature leads to a lower CO2-fixation rate with hydrogen. © 1969 Springer-Verlag.