Carbon Isotope Fractionation of 11 Acetogenic Strains Grown on H2and CO2

Abstract

ABSTRACTAcetogenic bacteria are able to grow autotrophically on hydrogen and carbon dioxide by using the acetyl coenzyme A (acetyl-CoA) pathway. Acetate is the end product of this reaction. In contrast to the fermentative route of acetate production, which shows almost no fractionation of carbon isotopes, the acetyl-CoA pathway has been reported to exhibit a preference for light carbon. InAcetobacterium woodiithe isotope fractionation factor (ε) for13C and12C has previously been reported to be ε = −58.6‰. To investigate whether such a strong fractionation is a general feature of acetogenic bacteria, we measured the stable carbon isotope fractionation factor of 10 acetogenic strains grown on H2and CO2. The average fractionation factor was εTIC= −57.2‰ for utilization of total inorganic carbon and εacetate= −54.6‰ for the production of acetate. The strongest fractionation was found forSporomusa sphaeroides(εTIC= −68.3‰), the lowest fractionation forMorella thermoacetica(εTIC= −38.2‰). To investigate the reproducibility of our measurements, we determined the fractionation factor of 21 biological replicates ofThermoanaerobacter kivui. In general, our study confirmed the strong fractionation of stable carbon during chemolithotrophic acetate formation in acetogenic bacteria. However, the specific characteristics of the bacterial strain, as well as the cultural conditions, may have a moderate influence on the overall fractionation.