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


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 (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 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 and Co0) selectively reduce CO2 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 CO2 and at temperatures from 30 to 100 °C. Geochemical CO2 fixation from native metals could have supplied critical C2 and C3 metabolites before the emergence of enzymes.

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Fig. 1: Mechanistic outline of the ATP-independent AcCoA pathway found in archaea.
Fig. 2: Carbon fixation by metals under hydrothermal conditions.
Fig. 3: Effect of temperature, pressure and reaction time on iron-promoted CO2 fixation in aqueous solution.
Fig. 4: Plausible mechanism for carbon fixation on the surface of Fe0 accounting for the detection of formate, methanol, acetate and pyruvate in aqueous solution upon hydrolysis with KOH.
Fig. 5: Hypothetical ancestral proto-anabolic network consisting of a hybrid of the AcCoA pathway and the rTCA cycle, showing the role of its intermediates as universal biosynthetic precursors.


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This project has received funding from the European Research Council under the European Union’s Horizon 2020 research and innovation programme (grant agreement 639170). Further funding was provided by a grant from LabEx ‘Chemistry of Complex Systems’. L. Allouche, M. Coppe and B. Vincent are gratefully acknowledged for assistance with the NMR experiments. We thank E. Smith and W. F. Martin for critical readings of this manuscript.

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Authors and Affiliations



J.M. supervised the research and the other authors performed the experiments. All authors contributed intellectually throughout the study. J.M. and K.B.M wrote the paper, and S.J.V. and K.B.M. assembled the Supplementary Information. Important preliminary experiments were carried out by P.C.

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Correspondence to Joseph Moran.

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Supplementary Methods, Supplementary Figures 1–35, Supplementary Tables 1–19

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Varma, S.J., Muchowska, K.B., Chatelain, P. et al. Native iron reduces CO2 to intermediates and end-products of the acetyl-CoA pathway. Nat Ecol Evol 2, 1019–1024 (2018).

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