Summary
The discovery of Asgardaeota archaea, the closest extant relative of eukaryotes to date, has reignited the two-domain of life theory. While it is apparent that Asgardaeota encode multiple eukaryotic-specific proteins, the lack of genomic information and metabolic characterization has precluded inferences about the closest eukaryotic ancestor and the metabolic landscape that laid the grounds for the emergence of the hallmark eukaryotic subcellular architecture. Here, we propose that Heimdallarchaeia (phylum within Asgardaeota) are the closest extant relatives to all eukaryotes and shed light on their facultative aerobic lifestyle, characterized by the capacity to use Sun’s energy and aerobic metabolic pathways unique among archaea. Remarkably, the visualization of Heimdallarchaeia organisms revealed a compacted genetic material that is highly unusual for prokaryotes at large. Our results support an evolutionary model in which both protoeukaryote ancestors (archaeal and bacterial) possessed the metabolic repertoire for oxygenic respiration and point towards a late mitochondrial acquisition.