Asgard Archaea: The Bizarre Microbes Unlocking Life’s Origins

In June, Emily Aguilar-Pine undertook a 2,500-kilometer journey from Bozeman, Montana, to Austin, Texas, transporting one of microbiology’s most prized specimens. Her mother’s SUV carried a small bottle labeled ‘hopes and dreams,’ containing roughly 30 milliliters of fluid housing _Skadiarchaeum cthulhuensis_, provisionally named Skadi. This organism belongs to the Asgard group of archaea, microorganisms named after the Norse divine realm. Aguilar-Pine kept the sample with her in the hotel room throughout the trip. “It was with me at all times,” she stated.

Since their initial discovery in 2015 via DNA extracted from North Atlantic sediments, Asgard archaea have fundamentally altered scientific understanding of eukaryotic origins. Eukaryotes, which encompass plants, animals, fungi, and protists, evolved from prokaryotes. While a link to archaea was previously suspected, genomic analysis now indicates that Asgards are the specific ancestral lineage of all eukaryotes. Consequently, many researchers now view life as existing within two primary domains: bacteria and archaea, with eukaryotes representing a branch within the latter.

Historically, knowledge of these microbes relied on environmental DNA sequencing. Despite identifying hundreds of species globally, their low abundance in nature made isolation challenging. However, recent breakthroughs have allowed scientists to establish stable cultures visible under microscopes. The first successful cultures emerged in 2020 and 2022, with additional announcements following in 2025. Skadi, for instance, was cultivated by PhD student Stavros Trimmer at Montana State University before being transferred to the University of Texas at Austin.

“Asgard are by far the coolest thing to happen to microbiology in the last 30 to 40 years,” said Paul Carini, a microbiologist at the University of Arizona. His lab is currently studying an unpublished culture from an Oregon estuary. Researchers are examining the unusual morphology and behavior of these cells to uncover the mechanisms behind the evolution of complex life.

The emergence of eukaryotic features—such as membrane-bound nuclei and specialized organelles—approximately two billion years ago opened new evolutionary pathways. These structures allow for protected DNA, localized cellular tasks, and efficient energy production via mitochondria. The prevailing theory suggests this transition occurred when an ancient Asgard archaeon engulfed a free-living bacterium, establishing an endosymbiotic relationship that eventually produced mitochondria.

Culturing these organisms has revealed surprising physical traits. Hiroyuki Imachi and Masaru Nobu at the Japan Agency for Marine-Earth Science and Technology spent over a decade growing _Promethearchaeum syntrophicum_, reporting the first successful Asgard culture in 2020. They initially dismissed unusual tentacle-like protrusions as contamination, but subsequent observations confirmed their authenticity.

Similarly, Christ Schleper’s team at the University of Vienna took six years to culture _Lokiarchaeum ossiferum_ from Slovenian sediments. Martin Pilhofer of ETH Zurich described the cells as unlike anything previously seen, noting the absence of rigid protein shells or double membranes. Instead, these cells possess actin-like cytoskeletal filaments and microtubules, features previously thought exclusive to eukaryotes.

Recent studies suggest these protrusions serve critical functions. Live microscopy has shown _L. ossiferum_ and _Margulisarchaeum peptidophilum_ crawling by reshaping their cytoskeletons. Inhibiting actin-like proteins halted this movement. Furthermore, protrusions appear to facilitate attachment to methane-producing partner microbes, potentially capturing and retaining them. This interaction raises the possibility that such structures played a pivotal role in the engulfment events that gave rise to eukaryotes.

“It is of course very exciting at the moment,” Schleper remarked. “Whenever I look at our cells, and we do more experiments, we get so surprised. We always find something that we did not even think of.” As research continues, these enigmatic microbes offer unprecedented insights into the foundational moments of complex life on Earth.