Carbon-Metal Bonds: Rare and Primordial in Metabolism

Submarine hydrothermal vents are rich in hydrogen (H₂), an ancient source of electrons and chemical energy for life. Geochemical H₂ stems from serpentinization, a process in which rock-bound iron reduces water to H₂. Reactions involving H₂ and carbon dioxide (CO₂) in hydrothermal systems generate abiotic methane and formate; these reactions resemble the core energy metabolism of methanogens and acetogens. These organisms are strict anaerobic autotrophs that inhabit hydrothermal vents and harness energy via H₂-dependent CO₂ reduction. Serpentinization also generates native metals, which can reduce CO₂ to formate and acetate in the laboratory. The enzymes that channel H₂, CO₂, and dinitrogen (N₂) into methanogen and acetogen metabolism are the backbone of the most ancient metabolic pathways. Their active sites share carbon-metal bonds which, although rare in biology, are conserved relics of primordial biochemistry present at the origin of life.