Carbon Isotope Fractionation by Autotrophic Bacteria with Three Different C0₂ Fixation Pathways

Abstract

Abstract Carbon isotope fractionation during autotrophic growth o f different bacteria which possess different autotrophic CO 2 fixation pathways has been studied. 13 C / 12 C -Ratios in the cell carbon of the following bacteria were determined (CO 2 fixation pathway suggested or proven in paren­theses): Alkaligenes eutrophus (reductive pentose phosphate cycle), Desulfobacterium autotrophicum and Acetobacterium woodii (reductive acetyl-CoA pathway), Desulfobacter hydrogenophilus and Thermoproteus neutrophilus (reductive citric acid cycle). The Δδ 13 C values, which indicate the per mille deviation of the 13 C content of cell carbon from that of the CO : used as the sole carbon source, range from - 10% ° (reductive citric acid cycle) over - 26% ° (reductive pentose phosphate cycle) to -36% ° (reductive acetyl-CoA pathway). Acetate formed via the acetyl-CoA pathway by the acetogenic Acetobacterium woodii showed a Δδ 13 C = -40% °. These data are discussed in view of the different CO 2 fixation reactions used by the bacteria and especially with regard to the isotopic composition of sedimentary carbon through time.