Scientists report new genomic evidence that strengthens the long-standing idea that complex cells (eukaryotes) arose when two very different microbes came together — and that oxygen played a role earlier than many researchers assumed. A team that sequenced and analysed thousands of environmental genomes found hundreds of new members of the Asgard archaeal group, including many Heimdallarchaeia closely related to eukaryotes, and discovered genes and protein structures consistent with oxygen-using metabolism in these lineages. (nature.com)
The study, published in Nature on February 18, 2026, assembled 404 Asgard metagenome-assembled genomes, 136 of which are new Heimdallarchaeia. The genomes are globally widespread and many come from shallow, variably oxygenated coastal sediments rather than only oxygen-free deep-sea settings. Detailed metabolic reconstructions show these Heimdallarchaeia encode components of an electron transport chain (including complex IV), haem biosynthesis pathways and enzymes for detoxifying reactive oxygen species — all hallmarks of an aerobic lifestyle. (nature.com)
Those findings help resolve a core puzzle about eukaryote origins: how an ancestral archaeon and an alphaproteobacterial partner that would become the mitochondrion ever met, given most Asgards had been sampled from anoxic environments. If the Asgard-eukaryotic ancestor already tolerated or used oxygen and lived in oxygen-variable coastal zones, physical proximity to oxygen-respiring bacteria becomes more plausible. The authors propose an updated, Heimdallarchaeia-centric model of eukaryogenesis in which both hydrogen metabolism and aerobic respiration could have been present in the archaeal ancestor. (astrobiology.com)
The Nature team also used structural predictions (with tools such as AlphaFold2) to compare archaeal proteins with eukaryotic counterparts, strengthening functional links between specific Asgard proteins and energy-conserving, oxygen-related processes found in eukaryotes. This structural evidence complements the genomic catalog and suggests bioenergetic capacities in Asgards that would favour the evolution of cellular complexity. (astrobiology.com)
Separate work from MIT offers an independent but related angle: molecular-clock analyses of a key oxygen-processing enzyme suggest the capacity to reduce oxygen evolved hundreds of millions of years before the Great Oxidation Event (~2.3 billion years ago). That study argues early microbes near oxygen-producing cyanobacteria could have consumed nascent oxygen locally, delaying its atmospheric accumulation while already developing aerobic pathways. Together with the Asgard results, the picture emerges of early life rapidly experimenting with oxygen metabolism long before oxygen became abundant in the air. (sciencedaily.com)
If upheld by future laboratory work and fossil constraints, these genomic and molecular-clock findings shift the narrative of eukaryote origins. They place key bioenergetic innovations — oxygen tolerance and more efficient respiration — at the archaeal side of the story and situate the cradle of eukaryogenesis in oxygen-variable habitats where symbiotic partnerships and metabolic handoffs were ecologically feasible. (nature.com)
Original Source: https://www.geneonline.com/study-supports-theory-of-symbiotic-merger-between-microorganisms-as-origin-of-complex-life/
Category:
Tags:
Publish Date: 2026-02-19 11:26:00
