The iron nitrogenase reduces carbon dioxide to formate and methane under physiological conditions: A route to feedstock chemicals.

Nitrogenases are the only known enzymes that reduce molecular nitrogen (N ₂ ) to ammonia. Recent findings have demonstrated that nitrogenases also reduce the greenhouse gas carbon dioxide (CO ₂ ), suggesting CO ₂ to be a competitor of N ₂ . However, the impact of omnipresent CO ₂ on N ₂ fixation has not been investigated to date. Here, we study the competing reduction of CO ₂ and N ₂ by the two nitrogenases of Rhodobacter capsulatus , the molybdenum and the iron nitrogenase. The iron nitrogenase is almost threefold more efficient in CO ₂ reduction and profoundly less selective for N ₂ than the molybdenum isoform under mixtures of N ₂ and CO ₂ . Correspondingly, the growth rate of diazotrophically grown R. capsulatus strains relying on the iron nitrogenase notably decreased after adding CO ₂ . The in vivo CO ₂ activity of the iron nitrogenase facilitates the light-driven extracellular accumulation of formate and methane, one-carbon substrates for other microbes, and feedstock chemicals for a circular economy.