Carbon isotope effects associated with autotrophic acetogenesis
The carbon kinetic isotope effects associated with synthesis of acetate from CO 2 and H 2 during autotrophic growth of Acetobacterium woodii at 30°C have been measured by isotopic analyses of CO 2 , methyl-carbon, and total acetate. Closed systems allowing construction of complete mass balances at varying stages of growth were utilized, and the effects of the partitioning of carbon between CO 2 and HCO 3 − were taken into account. For the overall reaction, total carbonate → total acetate, isotope effects measured in replicate experiments ranged from −59.0 ± 0.9% to − 57.2 ± 2.3 z %. Taking into account all measurements, the weighted mean and standard deviation are −58.6 ± 0.7%. There is no evidence for intramolecular ordering in the acetate. The carbon isotopic composition of sedimentary acetate, otherwise expected to be near that of sedimentary organic carbon, is likely to be depleted in environments in which autotrophic acetogenesis is occurring.