Asgard Archaea Form Nanotube Links with Bacteria in Shark Bay Stromatolites

The team spent four years optimizing culture conditions before turning to electron cryotomography to image the microbes at nanometer resolution. Samples from living stromatolites revealed the archaeon producing vesicles and tube-like structures that contact the bacterium, while metabolic reconstructions showed complementary production of vitamins, amino acids and hydrogen. This matches the endosymbiotic model in which an archaeal host engulfed a bacterium that became the mitochondrion, yet supplies the first physical snapshot of such contact outside of genomics.

Asgard lineages were first identified in 2015 from deep-sea sediments; their genomes already hinted at eukaryotic signature proteins. The Shark Bay specimens add an ecological context where these organisms persist in oxygen-producing mats that have existed for 3.5 billion years. The inability to grow the archaeon in pure culture further supports obligate dependence on bacterial partners, a trait that may have stabilized early cooperative metabolisms.

The study stops short of proving engulfment occurred; nanotubes could represent nutrient exchange rather than the precursor to endosymbiosis. Larger metagenomic surveys across additional hypersaline sites and time-series imaging of live consortia would strengthen causal claims. If replicated, the system offers a tractable model for testing whether such contacts trigger gene transfer or membrane remodeling.

Future work should combine single-cell genomics with live-cell fluorescence to track whether nanotube formation precedes or follows metabolic complementation, directly testing the sequence of events predicted by the symbiosis hypothesis.