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.