Isotope Fractionation in Photosynthetic Bacteria during Carbon Dioxide Assimilation 1

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RESUMO

The δ PDB13C 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 PDB13C 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 PDB13C 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.

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