Ancient Architects: How Bizarre Microbes Are Rewriting the Story of Complex Life

Posted on 18 September, 2026 by Mehrdad Fathi

When Emily Aguilar-Pine drove 2,500 kilometres from Montana to Texas in June 2026, she had a small bottle of liquid riding with her in the back of her mother’s SUV. The label read “hopes and dreams.” Inside was a living culture of an Asgard archaeon — arguably one of the most scientifically precious microbes on the planet. It slept in hotel rooms with her. She never let it out of sight.

That kind of devotion is not unusual in this field. Researchers who work with Asgard archaea speak about them the way astronomers speak about a signal from deep space: something that rewires your understanding of where you came from.

A Discovery That Rewrote the Tree of Life

Asgard archaea were first identified in 2015 from DNA extracted from sediments at the bottom of the North Atlantic — specifically from a hydrothermal vent field called Loki’s Castle. What the researchers found in those genomes was unexpected enough to force a rethink of one of biology’s most fundamental questions: how did complex life evolve?

The dominant model had long held that the complex eukaryotic cells underpinning all plants, animals, fungi, and protists arose when an ancient archaeon and a bacterium entered an endosymbiotic relationship roughly two billion years ago. The bacterium eventually became the mitochondrion. What remained unclear was which archaeon played host.

The Asgard genomes pointed to an answer. Embedded within them were genes encoding proteins previously thought to be exclusive to eukaryotes — the molecular machinery for building dynamic cytoskeletons, moving materials between cellular compartments, and reshaping membranes. The implication was stark: the ancestral host cell was not a primitive, featureless microbe. It already carried much of the toolkit that complex life would eventually run on. Most researchers now accept a two-domain model, in which eukaryotes are not a separate branch of life at all, but a lineage that grew out of the Asgards.

The Problem With Working From DNA Alone

For over a decade after the initial discovery, almost everything known about Asgard archaea came from environmental sequencing — piecing together genomes from DNA fragments recovered from sediment and seawater. Hundreds of species have been identified this way, from hydrothermal vents to freshwater lakes to coastal mudflats. But the organisms themselves remained largely out of reach. They grow slowly, in small numbers, in environments hostile to oxygen and standard laboratory conditions.

The first successful culture was reported in 2020 by microbiologists Hiroyuki Imachi and Masaru Nobu at the Japan Agency for Marine-Earth Science and Technology. Their organism, Promethearchaeum syntrophicum, had been growing in a bioreactor for twelve years before they realized what they had. The original project predated the discovery of Asgards entirely.

Since then, the pace has accelerated. Four additional cultures have been announced since the start of 2025. Several more exist in labs around the world — including Skadi, the culture Aguilar-Pine carried across the American Southwest — and have not yet appeared in the scientific literature. And the cells researchers are now observing under microscopes are, by every account, like nothing seen before.

Tentacles, Compartments, and a Cell That Moves

The defining visual feature of cultured Asgard archaea is a set of protrusions — thin, branching extensions that jut from the spherical cell body like tentacles, or antlers, depending on who is describing them. They appear in nearly every culture that has been successfully imaged.

When Christa Schleper’s group at the University of Vienna published the second cultured Asgard in 2022, cell biologist Martin Pilhofer at ETH Zurich examined the imaging data. “I was completely shocked,” he later recalled. The organism — provisionally named Lokiarchaeum ossiferum — had protrusions, no rigid cell wall, and internal filaments built from actin-like proteins. A subsequent paper reported microtubules as well. Both features are hallmarks of the eukaryotic cytoskeleton.

What the protrusions actually do has been the subject of intense interest. A preprint from late 2025 offered the first direct evidence: live microscopy captured L. ossiferum and a second species, Margulisarchaeum peptidophilum, crawling by dynamically reshaping the actin-like filaments within their protrusions. When those proteins were chemically inhibited, movement stopped. A separate study from Imachi and Nobu observed protrusions making physical contact with methane-producing partner microbes through surface spikes — suggesting the extensions may help Asgard cells capture and maintain their metabolic partners.

The possibility that these protrusions were involved in the original endosymbiotic event has become one of the most discussed ideas in the field. Cell biologist Buzz Baum at the MRC Laboratory of Molecular Biology in Cambridge and evolutionary biologist David Baum at the University of Wisconsin-Madison proposed a model in 2014 in which an ancient archaeon used such protrusions to wrap around and eventually engulf a free-living bacterium — the reverse of the classical membrane-folding model. The physical behavior now being observed in cultured cells fits that hypothesis.

Equally striking is recent work from Buzz Baum’s group, reported in a preprint in late 2025. Imaging of a Heimdallarchaeia-class Asgard — the group currently considered most closely related to eukaryotes — revealed compartments within the cell body, and compartments within those compartments. Internal membrane structure was thought to be a eukaryotic innovation. Seeing it in an archaeon is, as Baum described it, “probably the most exciting thing my lab has ever discovered.”

In Shark Bay, Western Australia, yet another cultured species — Nerearchaeum marumarumayae — showed chains of vesicles dangling from its cell body and a thin physical tube reaching out from a bacterial partner to make direct contact. “I couldn’t believe I was seeing a physical interaction,” said Debnath Ghosal at the University of Melbourne, who led the imaging. What is exchanged across that connection, if anything, remains unknown.

Cultivating the Uncultivatable

Growing Asgard archaea is, in the words of microbiologist Paul Carini at the University of Arizona, “riddled with inconsistency and ambiguity.” The cells hate oxygen, grow at extreme slowness, and reach densities too low for most standard analyses. Managing a culture often means managing an entire microbial community simultaneously, since Asgards have so far been grown only alongside partner species they depend on metabolically.

Stavros Trimmer, the PhD student who cultivated Skadi at Montana State University, went 193 days before his enrichment was stable enough to transfer 10% of the culture to fresh medium. The next transfer took 173 days. Then 90. He has described the experience as resembling dating in your 20s: high highs, then heartbreak, then an unexpected recovery just when you are about to give up.

Reproducibility across labs is a real challenge. Techniques that work in one environment may fail entirely in another, and the precariousness of cultures has contributed to friction over sharing. Imachi and Nobu have deposited strains in a public collection in Japan, making them accessible to any research group. But very few repositories worldwide can accommodate anaerobic, multispecies cultures, and transfer is itself a technical obstacle.

Thijs Ettema at Wageningen University, who led the original 2015 discovery, now devotes half his lab to cultivation. He frames the current data as necessarily incomplete. “We need to stay open-minded,” he says. The cultured Asgards represent only a handful of lineages out of hundreds identified through sequencing. Each new organism so far has brought surprises. There is no particular reason to think the surprises are finished.

The Oxygen Question

One of the liveliest open debates concerns the metabolic environment in which the original eukaryote-generating endosymbiotic event occurred. The classical account places it during a period of rising atmospheric oxygen, roughly two billion years ago. But the ancestral archaeon may have been an anaerobe encountering an aerobic bacterium for the first time — or it may have already tolerated or used oxygen.

Heimdallarchaeia carry genes involved in oxygen transport and aerobic respiration. Imachi and Nobu recently found that M. peptidophilum can tolerate limited oxygen in the presence of oxygen-using partners. Whether this represents an ancestral trait or a later adaptation is unclear. Answering the question properly will require culturing a broader range of Asgard lineages and tracking their metabolic behavior directly — work that is underway in multiple labs but measured in years, not months.

What Comes Next

The goal most researchers converge on is a model organism: a single Asgard strain that multiple labs can grow, share, and manipulate genetically, allowing different teams to replicate and build on each other’s results. That kind of standardization has not yet been achieved. Schleper’s group has identified a virus in an L. ossiferum culture that may one day serve as a genetic tool, offering a path toward the deliberate introduction and modification of genes.

Trimmer is moving in a different direction for now. He has spent two weeks training Aguilar-Pine to care for Skadi, and is looking for more labs to take on the culture. The reasoning is straightforward: more hands, more variation in conditions, more chances to find what makes these cells thrive. “The more people are going to find tips and tricks,” he says. “It’s only going to benefit the community.”

For researchers who have spent years coaxing a few millilitres of ancient-lineage cells into something observable, the payoff is not just scientific. There is something almost vertiginous about watching a cell move, extend a protrusion, and touch a partner — and recognizing that a distant ancestor of that cell, performing something like the same gesture two billion years ago, may be the reason you exist.

Source: Nature 657, 587–589 (2026). doi: https://doi.org/10.1038/d41586-026-02849-y

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