Researchers from Heinrich Heine University in Düsseldorf have reconstructed an ancient metabolic network that was common to all modern living organisms.
The result was surprising, as scientists concluded that cellular life originated on Earth at least twice.
Researchers compared the genes of bacteria and archaea, two major domains of life, and discovered that the same chemical reactions are carried out by different proteins in each. This means, according to the researchers, that these reactions predate proteins; minerals and inorganic materials initially acted as catalysts, and later, evolution "invented" enzymes, but in different ways in each of the two domains of life.
The study methodology is based on comparing the genes that encode metabolic enzymes in bacteria and modern archaea. Scientists identified a common set of reactions inherited from their last common ancestor, LUCA, but they also discovered that both groups developed unique protein catalysts to carry out the same chemical reactions. According to the study authors, this suggests that the reactions predate the proteins, as minerals and inorganic compounds initially acted as catalysts before evolution led to the emergence of specialized proteins that took over these functions.
The study authors focused particularly on the interaction of phosphites with organic molecules, arguing that this was a crucial turning point, linking geochemical processes to biochemical ones and explaining why phosphorus occupies such a central position in cellular metabolism. Mineral catalysts gradually declined, replaced by more specialized and efficient enzymes, but this substitution occurred independently and along different pathways in the two evolutionary lineages.
Researchers believe that the last common ancestor, LUCA, was not a fully formed cell, but rather a chemically active system. Bacteria and archaea independently developed their own cell membranes, cell division mechanisms, and energy production systems.
However, this hypothesis has not gained widespread acceptance. Crystallographer Juan Fontesella-Camps believes that the last common ancestor, LUCA, may have possessed a primitive membrane, meaning that cellular life arose only once. Microbiologist Donato Giovanelli described the study as compelling but speculative, noting that it is impossible to fully reconstruct the details of events that occurred billions of years ago.
