A fundamental discovery about the origin of life on Terra was recently published in the journal Nature by researchers from Universidade of Texas in Austin. The study details how ancestral microorganisms, known as archaea Asgard, already had the ability to metabolize oxygen long before the symbiosis that gave rise to today’s complex cells. The revelation changes the understanding of the evolutionary steps that allowed the emergence of plants, animals and fungi.
The genetic analysis focused on a specific group called Heimdallarchaeia, considered the closest microbial relative of all eukaryotic organisms. Utilizando artificial intelligence and advanced sequencing of DNA recovered from marine sediments, the team identified genes responsible for aerobic respiration in these ancient lineages. The data indicate that the transition to complex life was not an abrupt event, but rather a gradual process of chemical adaptation.
The results resolve a long-standing scientific debate about how an anaerobic host could have fused with an oxygen-dependent bacterium. Anteriormente, it was believed that this union would be biologically incompatible without prior preparation. The study demonstrates that the common ancestor already exploited the oxygen available in the environment, facilitating the integration of the bacteria that would become the mitochondria.
This metabolic adaptation offered decisive energetic advantages. The ability to process oxygen allowed the generation of more cellular energy, an essential fuel to sustain larger and more complex organisms. Research suggests that these features evolved in direct response to changes in Earth’s early atmosphere.
Genetic mapping and use of artificial intelligence
To reach these conclusions, scientists compiled and analyzed more than 13,000 new microbial genomes collected on several ocean expeditions around the world. The volume of data processed was massive, involving around 15 terabytes of raw genetic sequencing to filter relevant information about cellular evolution and identify hidden patterns in the genetic code.
The use of the AlphaFold2 tool was decisive for validating the findings, as it allowed the prediction of the three-dimensional structures of the proteins found in the Heimdallarchaeia archaea. When comparing these structures with those of modern organisms, the similarity with the proteins used in current oxidative metabolism became evident, confirming the evolutionary connection.
Crucial components, such as Complexo I subunits and membrane hydrogenases, presented highly conserved configurations. Essas structures are fundamental to the efficient generation of proton motive force, a vital mechanism for energy production at the cellular level.
Furthermore, the team was able to recover hundreds of new genomes from water column and sediment samples, drastically expanding the genetic catalog of the Asgardarchaeota group. The identification of 136 additional Heimdallarchaeia genomes has nearly doubled the available knowledge about this specific lineage.
Adaptation to oxygen and evolutionary advantages
The ability to use oxygen in cellular respiration generates much more ATP — the energy currency of life — than traditional anaerobic processes. Essa extra efficiency provided the metabolic support necessary for the development of more complex and robust cellular structures over millions of years, allowing life to stop being just microscopic and simple.
Evidence suggests that these archaea lived in shallow coastal sediments and the water column, environments where oxygen levels varied, forcing a direct evolutionary adaptation. Diferente of other lineages that remained in deep zones without oxygen, the Heimdallarchaeia found niches where aerobic respiration was possible and advantageous.
Defense mechanisms have also been identified, such as enzymes for heme biosynthesis and detoxification of reactive oxygen species. Essas Biological tools were essential for protecting cells against oxidative damage, especially during the period known as Grande Evento of Oxidação, which radically altered the planet’s chemistry.
Reconfiguration of endosymbiotic theory
The predominant scientific model describes the origin of eukaryotes through endosymbiosis, where an archaea hosted a bacterium that eventually became mitochondria. The new discovery refines this theory, indicating that the host was not a passive or strictly anaerobic organism, but a being already pre-adapted to oxygen consumption.
With the new data, it is understood that the host Asgard had partial aerobic pathways that facilitated the integration and control of the bacterial symbiont. Essa metabolic compatibility would have been key to the fusion’s success, allowing the new hybrid cell to thrive in an increasingly oxygenated world.
The temporal coincidence between the increase in oxygen levels in the atmosphere, around 2.4 billion years ago, and the emergence of eukaryotic microfossils reinforces the hypothesis. Oxygen was not just an environmental byproduct, but an active engine that drove biological complexity through these archaeal lineages.
- Heimdallarchaeia has the genetic code for heme biosynthesis.
- Lineage presents robust defense mechanisms against oxidative damage.
- Identified proteins are similar to mitochondrial complexes III and IV.
- Organisms preferentially occur in niches with the presence of oxygen.
