Scientists from Universidade of Texas in Austin published in the magazine Eles identified that certain archaea Asgard, considered close ancestors of eukaryotes, have metabolic pathways that use oxygen, even living in environments with oxygen present. Essa ability resolves the paradox of how an anaerobic host could unite with an aerobic bacteria that became the mitochondria.
The research drastically expanded knowledge about the genetic diversity of the Asgard archaea. The team recovered hundreds of new genomes from environmental DNA collected in marine sediments and the water column. Esses data showed that lineages closer to eukaryotes, such as Heimdallarchaeia, encode proteins for aerobic respiration and protection against oxidative damage.
The comparative analysis of protein structures, carried out with the aid of artificial intelligence, confirmed similarities between proteins from these archaea and those from modern eukaryotic cells. The results indicate that the common ancestor was already exploiting oxygen before the symbiotic fusion. Essa adaptation offered energetic advantages that allowed the development of complex cellular structures.
Expansion of known genetic diversity
The team gathered more than 13,000 new microbial genomes from samples from ocean expeditions. The processing involved around 15 terabytes of environmental DNA sequencing.
The researchers identified 136 additional genomes from Heimdallarchaeia. Essa expansion almost doubled the genetic catalog of the Asgardarchaeota group.
Phylogenetic analyzes have positioned Heimdallarchaeia as the closest branch to eukaryotes. Elas have a greater number of genes related to aerobic metabolism.
Oxygenated environments predominate in close lineages
Heimdallarchaeia frequently occurs in shallow coastal sediments and in the oceanic water column. Esses habitats have dissolved oxygen at varying levels.
Most other archaea live in deep, anoxic parts of the ocean. The differential distribution suggests evolutionary adaptation to the increase in oxygen in the early atmosphere.
Metabolic advantages of oxygen
The use of oxygen in cellular respiration generates much more ATP than anaerobic processes. Essa energy efficiency was crucial to the transition to cellular complexity.
Proteins identified in Heimdallarchaeia include components of electron transport chain complexes. Elas resemble those found in eukaryotic mitochondria.
The presence of enzymes for heme biosynthesis and detoxification of reactive oxygen species reinforces the ancestral aerobic capacity. Esses mechanisms protected cells during Grande Evento from Oxidação.
Symbiosis between Asgard and alphaproteobacteria
The current model describes eukaryotic origin as the result of endosymbiosis between an archaea Asgard and an alphaproteobacterium. The bacteria evolved into mitochondria, allowing efficient energy production.
The discovery indicates that the host Asgard already had partial aerobic pathways. Essa pre-adaptation facilitated the integration and control of the symbiote.
Temporal context of eukaryotic emergence
The Grande Evento of Oxidação raised atmospheric oxygen levels about 2.4 billion years ago. Microfósseis eukaryotes appear in the fossil record shortly after this increase.
The temporal coincidence supports the hypothesis that oxygen drove the evolution of complexity. Asgard archaea adapted to oxygen fit into this evolutionary scenario.
Using AlphaFold for Protein Analysis
The AlphaFold2 tool predicted three-dimensional structures of Heimdallarchaeia proteins. Comparisons revealed high similarity with eukaryotic proteins of oxidative metabolism.
Components such as Complexo I subunits and membrane hydrogenases showed conserved configurations. Essas structures increase efficiency in generating proton motive force.
The study included international collaborations and support from scientific foundations. The findings expand the understanding of the prokaryote-eukaryote transition.
- Heimdallarchaeia encodes heme biosynthesis
- Has defense mechanisms against ROS
- Presents complexes similar to mitochondrial III and IV
- Preferentially occurs in oxygenated niches
