FIG 3.

Mixotrophic growth of Thermoanaerobacter kivui DSM 2030 on formate and H₂/CO₂ leads to the incorporation of both substrates. The analytes measured—CO₂, formate (Form), and acetate (Ac)—are given in parentheses in the key. H₂/CO₂ concentrations were 2.5 mmol/bottle (H₂) and 0.6 mmol/bottle (CO₂) in the H₂/CO₂ treatment as well as in the low- and high-mix treatments (incubations in the presence of a low or a high concentration of formate, respectively, under a headspace of H₂CO₂). Formate concentrations were 0.25 mmol/bottle in the low-mix treatment and 1 mmol/bottle in the high-mix and formate treatments. The δ¹³C value of the released acetate is a direct result of the mixing of the δ¹³C values of the substrates, while the fractionation of the individual substrates is quite constant. Values are averages for three independent replicates ± standard deviations.