Summary
Researchers are culturing Asgard archaea, rare microbes whose genomes link them to the ancestors of eukaryotic cells. Microscopy is revealing cell protrusions, movement and possible partnerships that may illuminate how complex life began.
Researchers are bringing several rare Asgard archaea into relatively stable laboratory cultures, making it possible to examine cells that were previously known mainly through fragments of environmental DNA. Microscopy has revealed tentacle-like protrusions, internal scaffolding and interactions with other microbes—features that could help explain how the first complex cells evolved.
Asgard archaea were identified in 2015 from DNA recovered from North Atlantic sediments. Hundreds of species have since been detected in environmental samples, but they occur in such low numbers and grow so slowly that isolating them has been exceptionally difficult. The first laboratory cultures were reported in 2020 and 2022, followed by four more announced since the beginning of 2025.
These are culture and imaging studies of microbial cells. Some of the newest observations come from preprints, while other cultures are still unpublished.
What researchers are seeing in culture
The most striking feature is a set of thin protrusions extending from the cells’ usually spherical bodies. They have been observed in almost every established Asgard culture. The structures can resemble tentacles or antlers and appear to require substantial cellular resources to build and maintain.
The first cultured species, Promethearchaeum syntrophicum, was grown in a co-culture with a methane-producing archaeon. Its protrusions were initially suspected to be contamination or an imaging artefact, but repeated observations have shown that they are genuine cellular structures.
A second species, provisionally named Lokiarchaeum ossiferum, has an actin-like cytoskeleton and microtubules—components associated with the dynamic internal scaffolding of eukaryotic cells. It also lacks the rigid protein shell common in many archaea and bacteria, as well as the double membrane or cell wall characteristic of eukaryotic cells.
Live microscopy reported in a late-2025 preprint showed L. ossiferum and Margulisarchaeum peptidophilum moving across surfaces by reshaping the cytoskeleton in their protrusions. Inhibiting the actin-like proteins stopped that movement, linking the proteins to the cells’ ability to crawl.
Other observations point to possible partnerships. Researchers studying M. peptidophilum and Flexarchaeum multiprotrusionis saw protrusions attach to methane-producing partners through spike-like structures. In the Asgard species Nerearchaeum marumarumayae, researchers observed chains of vesicles outside the cell and a long tube extending from a partner bacterium towards it. The material exchanged between those microbes has not been determined.
Why these microbes matter for complex life
Eukaryotic cells—which include animals, plants, fungi and many single-celled organisms—have features that allow them to perform more specialised tasks than typical prokaryotic cells. Their DNA is enclosed in a nucleus, internal compartments organise different processes, and mitochondria provide energy through aerobic respiration. These features enabled larger cells, multicellular organisms and more complex forms of reproduction.
The prevailing evolutionary picture places the origin of eukaryotes roughly two billion years ago. In that account, an ancestral archaeal host formed a mutually beneficial endosymbiotic partnership with a free-living bacterium; the bacterium eventually became the mitochondrion. The precise route to that partnership remains unresolved, including how the cells met and how the bacterial partner became enclosed.
Genomic studies have made Asgard archaea central to this question. Their DNA contains genes for proteins once thought to be exclusive to eukaryotes, including proteins involved in cytoskeletal structure, membrane remodelling and the movement of proteins and lipids between cellular compartments. Most researchers studying the issue now place eukaryotes as a branch within the archaeal part of life’s history, rather than as a wholly separate equivalent to bacteria and archaea.
The cultured cells provide a way to test what those genes actually do. Their protrusions have also made an older evolutionary proposal more tangible: the “inside-out” model suggests that an ancestral archaeon may have used extensions of its cell surface to exchange resources with another microbe and eventually surround the precursor of the mitochondrion. That differs from a simple model in which the host cell folded its membrane inward to engulf the bacterium.
The cultures do not settle which route produced the first eukaryotic cell. They do, however, show that Asgard archaea possess more elaborate shapes, movements and microbial interactions than their environmental DNA alone revealed. As more species are grown, researchers can compare their proteins and cell behaviour directly, bringing the origin of complex life within reach of experimental cell biology rather than genome reconstruction alone.