A recent study published in the journal Science Advances last Wednesday (the 5th) proposes a fundamental change in the understanding of the origin of life: bacteria and archaea may have reached the state of living organisms through separate evolutionary paths.
The research, conducted by scientists from Heinrich Heine University in Düsseldorf, Germany, analyzed enzymes related to metabolism. The authors concluded that two major types of microorganisms developed their own solutions to overcome the critical stage between non-living chemistry and the first self-sustaining organisms.
This discovery suggests that the universal common ancestor, known as LUCA, may not be the sole starting point for cellular life. Instead, the history of life might have had two separate beginnings after the initial chemical stage.
The origin of life touches upon one of the most complex problems in science: how molecular complexes present on early Earth transformed into systems capable of obtaining energy, growing, and reproducing. Metabolism plays a central role in this process.
Although there are various definitions of life, the ability to carry out chemical reactions to maintain the functioning of an organism is considered an intrinsic characteristic of living beings. The scientific challenge lies in the evolutionary dilemma: enzymes, proteins that accelerate chemical reactions, are produced by living organisms, but the first living systems had to perform these reactions before such structures appeared.
Researchers hypothesize that extreme environments, such as hydrothermal vents, could have created the necessary conditions for this transition. In such places, natural metals might have acted as catalysts, facilitating the chemical reactions that led to the formation of molecules important for the genesis of life.
To test this hypothesis, the team studied protein structures present in the genomes of bacteria and archaea. Based on this data, the scientists developed a method to order enzymes by complexity level and assess the sequence of appearance of different metabolic components.
The results showed that LUCA likely possessed only a fraction of the enzymes required for modern metabolism. The remaining functions were initially performed by chemical elements of the surrounding environment.
According to the proposed reconstruction, the development of metabolism proceeded in stages. Initially, reactions were entirely dependent on natural catalysts, such as metals. Then, organisms in the early stages began to produce their own enzymes, gradually replacing external elements.
With development, these cellular structures gained greater chemical independence, reaching the stage of free cells capable of sustaining their metabolism without direct dependence on the environment for core reactions.
The main conclusion of the study involves comparing bacteria and archaea. According to the researchers, the enzymes responsible for certain vital metabolic functions did not originate from the same evolutionary source in both groups. This indicates that after the initial divergence, each group found its own mechanisms to perform similar processes, meaning the ability to sustain an independent cell arose twice.
The hypothesis does not exclude the existence of a common ancestor for all living things, but it suggests that this organism lived before the complete metabolic independence of cells. The divergence of evolutionary paths could have occurred during the transitional period between prebiotic chemistry and cellular life.
The study also examines the origin of the mechanisms used by organisms to obtain energy. One of the most crucial molecules in this process is ATP, which serves as a universal energy source for modern cells. Scientists suggest that the precursor to ATP could have existed in environments similar to hydrothermal vents. They note that reactions involving phosphite, a phosphorus compound naturally found in these locations, could have promoted phosphorylation processes before the emergence of modern biological systems.
Despite the progress, scientists emphasize the remaining questions regarding the precise environment in which these early stages occurred. Open problems remain concerning the role of water or other more viscous chemical media in forming the first systems capable of evolution.
If new research confirms these findings, the traditional view of the tree of life may require adjustment. Instead of a single root leading to all known organisms, the origin of cellular life might have involved two separate pathways that only converged in later evolutionary history.
