Carbon-Metal Bonds: Rare and Primordial in Metabolism

Submarine hydrothermal vents are rich in hydrogen (H-2), an ancient source of electrons and chemical energy for life. Geochemical H-2 stems from serpentinization, a process in which rock-bound iron reduces water to H-2. Reactions involving H-2 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 H-2-dependent CO2 reduction. Serpentinization also generates native metals, which can reduce CO2 to formate and acetate in the laboratory. The enzymes that channel H-2, CO2, and dinitrogen (N-2) 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.