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# Isotope Fractionation in Photosynthetic Bacteria during Carbon Dioxide Assimilation

William Wong, William M. Sackett and C. Roy Benedict
Plant Physiology
Vol. 55, No. 3 (Mar., 1975), pp. 475-479
Stable URL: http://www.jstor.org/stable/4263955
Page Count: 5
The δ ${}_{\text{PDB}}^{13}\text{C}$ values have been determined for the cellular constituents and metabolic intermediates of autotrophically grown Chromatium vinosum. The isotopic composition of the HCO3 - in the medium and the carbon isotopic composition of the bacterial cells change with the growth of the culture. The δ ${}_{\text{PDB}}^{13}\text{C}$ value of the HCO3 - in the media changes from an initial value of -6.6‰ to +8.1‰ after 10 days of bacterial growth and the δ ${}_{\text{PDB}}^{13}\text{C}$ value of the bacterial cells change from -37.5‰ to -29.2‰ in the same period. The amount of carbon isotope fractionation during the synthesis of hexoses by the photoassimilation of CO2 has a range of -15.5‰ at time zero to -22.0‰ after 10 days. This range of fractionation compares to the range of carbon isotope fractionation for the synthesis of sugars from CO2 by ribulose 1,5-diphosphate carboxylase and the Calvin cycle. The amount of carbon isotope fractionation during the synthesis of aspartic acid from CO2 is -24.9‰ at time zero and -15.0‰ after 10 days of bacterial growth. This amount of fractionation is in the range of carbon isotope fractionation for the synthesis of C4 amino acids by a double carboxylation through ribulose 1,5-diphosphate and phosphoenolpyruvate carboxylase.