Researchers at Heinrich Heine University Düsseldorf and their international collaborators have published findings in Science Advances proposing that the earliest forms of life on Earth may have emerged through two separate evolutionary pathways. The study focused on tracing the origins of enzymes and metabolic processes in the period before free-living cells fully developed, examining the divergence between bacteria and archaea approximately 4 billion years ago.
The research team analyzed complete metabolic networks comprising 420 chemical reactions that early cells would have used to produce essential biological components from materials available on primitive Earth, such as hydrogen gas, ammonia and carbon dioxide. A key discovery involved the role of the last universal ancestor of all cells, known as LUCA. The researchers found that LUCA possessed enzymes for only about half of these metabolic reactions, while the other half were catalyzed by metals present in the environment, particularly in hydrothermal vents. This indicates that early metabolism relied far more heavily on environmental chemistry than modern cellular processes do.
The study identified evidence that bacteria and archaea independently evolved structurally different enzymes to perform the same essential metabolic tasks. These parallel developments in enzymatic evolution may have been critical, potentially allowing the two lineages to gradually reduce their dependence on hydrothermal vent chemistry and eventually develop as autonomous living cells. This dual independent evolution provides support for the hypothesis of two separate origins of free-living cellular life.
The researchers also investigated energy sources for early metabolism, identifying palladium, a metal occurring naturally in hydrothermal vents, as a possible catalyst. When combined with phosphite, a phosphorus compound also found in these environments, palladium could generate metabolic phosphorylation reactions. This mechanism may explain how early metabolic processes obtained necessary energy before the evolution of modern biological energy systems based on ATP molecules.
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