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.