Carbon Isotope Fractionation during Catabolism and Anabolism in Acetogenic Bacteria Growing on Different Substrates.

ABSTRACT Homoacetogenic bacteria are versatile microbes that use the acetyl coenzyme A (acetyl-CoA) pathway to synthesize acetate from CO 2 and hydrogen. Likewise, the acetyl-CoA pathway may be used to incorporate other 1-carbon substrates (e.g., methanol or formate) into acetate or to homoferment monosaccharides completely to acetate. In this study, we analyzed the fractionation of pure acetogenic cultures grown on different carbon substrates. While the fractionation of Sporomusa sphaeroides grown on C 1 compounds was strong (e C1 , −49‰ to −64‰), the fractionation of Moorella thermoacetica and Thermoanaerobacter kivui using glucose (e Glu = −14.1‰) was roughly one-third as strong, suggesting a contribution of less-depleted acetate from fermentative processes. For M. thermoacetica, this could indeed be validated by the addition of nitrate, which inhibited the acetyl-CoA pathway, resulting in fractionation during fermentation (e ferm = −0.4‰). In addition, we determined the fractionation into microbial biomass of T. kivui grown on H 2 /CO 2 (e anabol. = −28.6‰) as well as on glucose (e anabol. = +2.9‰).