First Cultivation of Heimdallarchaeia, Our Closest Archaeal Relatives, Sheds Light on Eukaryote Origins

A team led by Hiroyuki Imachi and Masaru K. Nobu of the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) and Satoshi Nakagawa of Kyoto University has successfully isolated and cultivated two strains of Heimdallarchaeia. These archaea are considered among the closest known archaeal relatives of eukaryotes—the domain that includes all animals, plants, and fungi. The breakthrough, achieved after years of effort, opens new avenues for studying the evolutionary transition from simple microbes to complex cells. Heimdallarchaeia belong to the Asgard archaea, a group discovered in deep-sea sediments and hydrothermal vents. Their genomes contain many genes previously thought to be unique to eukaryotes, including those involved in membrane remodeling and intracellular trafficking. By growing these organisms in the lab, researchers can now directly observe their biology and test hypotheses about how eukaryotic features evolved. This is significant because the origin of eukaryotes remains one of biology's biggest mysteries. The cultivation was achieved using a novel bioreactor system that mimicked the low-oxygen, methane-rich conditions of deep-sea environments. The two strains, named after Norse mythology figures, grow extremely slowly, doubling only every few weeks. Despite this challenge, the team managed to maintain stable cultures, enabling detailed genomic and physiological analyses. Early results suggest that Heimdallarchaeia may form membrane protrusions, possibly resembling early stages of phagocytosis—a key eukaryotic trait. This discovery matters because it provides a missing link in the tree of life. Understanding how complex cells arose could illuminate fundamental aspects of biology, from cell organization to disease mechanisms. The work also highlights the importance of exploring extreme environments for novel life forms. As research progresses, these cultivated archaea may reveal the precise steps that led from simple prokaryotes to the diversity of life we see today.