Native iron reduces CO to intermediates and end-products of the acetyl-CoA pathway.

Autotrophic theories for the origin of life propose that CO was the carbon source for primordial biosynthesis. Among the six known CO fixation pathways in nature, the acetyl-CoA (AcCoA; or Wood-Ljungdahl) pathway is the most ancient, and relies on transition metals for catalysis. Modern microbes that use the AcCoA pathway typically fix CO with electrons from H, which requires complex flavin-based electron bifurcation. This presents a paradox: how could primitive metabolic systems have fixed CO before the origin of proteins? Here, we show that native transition metals (Fe, Ni and Co) selectively reduce CO to acetate and pyruvate-the intermediates and end-products of the AcCoA pathway-in near millimolar concentrations in water over hours to days using 1-40 bar CO and at temperatures from 30 to 100 °C. Geochemical CO fixation from native metals could have supplied critical C and C metabolites before the emergence of enzymes.