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

Abstract

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.