Native iron reduces CO(2) to intermediates and end-products of the acetyl CoA pathway

Autotrophic theories for the origin of life propose that CO(2) was the carbon source for primordial biosynthesis. Among the six known CO(2) fixation pathways in nature, the acetyl CoA (or Wood-Ljungdahl) pathway is the most ancient, and relies on transition metals for catalysis. Modern microbes that use the acetyl CoA pathway typically fix CO(2) with electrons from H(2), which requires complex flavin-based electron bifurcation. This presents a paradox: How could primitive metabolic systems have fixed CO(2) before the origin of proteins? Here we show that native transition metals (Fe(0), Ni(0), Co(0)) selectively reduce CO(2) to acetate and pyruvate, the intermediates and end-products of the AcCoA pathway, in near mM levels in water over hours to days using 1-40 bar CO(2) and at temperatures from 30-100 °C. Geochemical CO(2) fixation from native metals could have supplied critical C2 and C3 metabolites before the emergence of enzymes.