About four billion years ago, the basic chemistry that led to life likely started around hydrothermal vents. In these environments, natural metals helped drive reactions before cells had all their complex machinery.
Researchers at Heinrich Heine University Düsseldorf (HHU) and other institutions have traced this transition. They looked at how metabolism and enzymes changed as the ancestors of bacteria and archaea began to split apart.
Two Origins of Cellular Life
The study, published in Science Advances, explored the chemical network early cells used to create vital parts of life. It also investigated how these reactions got their energy. The scientists suggest that bacteria and archaea might have become free-living independently, even though they share the same basic genetic code.
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Start Your News DetoxNatalia Mrnjavac, a biologist at the University of Düsseldorf and lead author, explained what we might see if we went back in time. She said we would see two very different kinds of cells, pioneer bacteria and pioneer archaea, trying to live outside a hydrothermal vent for the first time.
Mrnjavac and her team compared genomes, protein structures, and chemical reactions. Their goal was to understand a very early stage of microbial evolution, before free-living cells existed.
William Martin, a biologist from Düsseldorf and senior author, noted that these comparisons offer new insights. They show how enzyme-catalyzed metabolism grew from spontaneous reactions driven by metals in the Earth's crust.
The researchers focused on the entire set of reactions cells use to build amino acids, RNA bases, and vitamins. These are made from simple substances found on early Earth, like hydrogen gas, ammonia, and CO2. This network, called metabolism, involves 420 reactions and is highly conserved across all life, similar to the genetic code.
Early Metabolism and Metal Catalysts
Martin pointed out a surprising finding: the enzymes for these reactions are not conserved between bacteria and archaea. He said the last universal ancestor of all cells (LUCA) only had enzymes for about half of these metabolic reactions. The other half were catalyzed by metals in LUCA's environment.
This suggests that early metabolism might have directly relied on its surroundings. Metals found naturally around hydrothermal vents could have performed tasks later taken over by biological catalysts.
Harun Tüysüz, an inorganic chemist, noted that metals in hydrothermal vents can replace many enzymes in metabolism. Joseph Moran from the University of Ottawa added that early biochemical evolution was a mix of enzymatic and metal catalysts.
Separate Solutions for Bacteria and Archaea
The researchers identified four stages in the early development of biological catalysis. It started with reactions driven only by metals, then a mix of metals and enzymes in LUCA. After that, the ancestors of bacteria and archaea diverged.
As these two lineages evolved, new enzymes took over reactions that once depended on inorganic catalysts from the environment.
Mrnjavac explained that the ancestors of bacteria and archaea independently developed different enzymes for the same essential metabolic reactions. She believes these parallel inventions might have led to the independent emergence of free-living bacteria and archaea.
Phosphite as an Early Energy Source
Another mystery was energy. Modern metabolism uses ATP, a complex molecule made by enzymes. So, ATP couldn't have been readily available to the earliest metabolic systems.
Manon Schlikker from the Düsseldorf team identified a new energy source for early metabolism. One possibility involves phosphite, a form of phosphorus found in hydrothermal vents. Palladium, a metal also found in these vents, acts as a catalyst.
Schlikker explained that reacting phosphite with organic compounds creates metabolic phosphorylation reactions in water overnight. Phosphite and palladium can replace ATP and enzymes, making early evolution easier to understand.
The team also had to figure out the order in which metabolism might have emerged. Because its 420 reactions are tightly connected, determining an order is complex.
Prof. Mike Steel and Prof. Daniel Huson developed a method to arrange metabolic reactions from simpler to more complex forms. This likely reflects their order of appearance in early evolution. Steel confirmed that a unique order exists, making the algorithm possible.
The findings suggest that the earliest cellular lineages became independent organisms at different times. The researchers believe bacteria and archaea separately transitioned from systems relying on their surroundings to free-living cells.
Martin concluded that the new data points to one origin for the genetic code, but two separate origins for life itself.
Deep Dive & References
Intermediate stages in the origin of metabolism at a phosphorylating hydrothermal vent - Science Advances, 2026
