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

Abstract

Nitrogenases are the only known enzymes that reduce molecular nitrogen (N₂) to ammonia. Recent findings have demonstrated that nitrogenases also reduce the greenhouse gas carbon dioxide (CO₂), suggesting CO₂ to be a competitor of N₂. However, the impact of omnipresent CO₂ on N₂ fixation has not been investigated to date. Here, we study the competing reduction of CO₂ and N₂ by the two nitrogenases of <i>Rhodobacter capsulatus</i>, the molybdenum and the iron nitrogenase. The iron nitrogenase is almost threefold more efficient in CO₂ reduction and profoundly less selective for N₂ than the molybdenum isoform under mixtures of N₂ and CO₂. Correspondingly, the growth rate of diazotrophically grown <i>R. capsulatus</i> strains relying on the iron nitrogenase notably decreased after adding CO₂. The in vivo CO₂ 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.