Native iron reduces CO2 to intermediates and end-products of the acetyl-CoA pathway.

Abstract

Autotrophic theories for the origin of life propose that CO2 was the carbon source for primordial biosynthesis. Among the six known CO2 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 CO2 with electrons from H2, which requires complex flavin-based electron bifurcation. This presents a paradox: How could primitive metabolic systems have fixed CO2 before the origin of proteins? Here we show that native transition metals (Fe0, Ni0, Co0) selectively reduce CO2 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 CO2 and at temperatures from 30-100 °C. Geochemical CO2 fixation from native metals could have supplied critical C2 and C3 metabolites before the emergence of enzymes.