In recent microscopic investigations, biologists identified a group nicknamed the archæa of Asgard. The discovery was reported by researchers affiliated with the University of Vienna, who describe a set of cells that challenge and enrich our understanding of the tree of life.
All known living organisms are traditionally grouped into three broad domains: eukaryotes, bacteria, and archaea. Eukaryotes include plants, animals, and fungi, and they are distinguished by the presence of a cell nucleus. In studies conducted in 2015, researchers analyzing deep-sea environmental samples uncovered a lineage of so-called Asgard archæa. On the evolutionary tree, these organisms occupy a position very close to eukaryotes, suggesting they are among the nearest relatives of nuclear organisms and possibly among the earliest precursors to multicellular life. This finding has sparked renewed interest in how complex cells evolved and how early symbiotic events may have paved the way for the diversity of life we see today.
Researchers from Austrian and Swiss laboratories employed electron microscopy to capture high-resolution images of cells that had been subjected to rapid freezing. The freezing technique preserves fine internal details, enabling a three-dimensional view of cellular architecture. The scientists describe cells that appear as rounded bodies connected by slender extensions, with some extensions forming intricate networks that hint at communication or attachment between neighboring cells. The images also reveal an extensive network of actin filaments, a feature historically associated with many eukaryotic cells and implicated in maintaining cell shape and enabling movement. These observations support the notion that certain Asgard archæa possess internal organization that shares important similarities with more complex life forms. [Citation: University of Vienna]
One candidate organism within this group is Lokiarchaeum ossiferum, which has frequently served as a model species for examining Asgard archæa. Within the studied samples, clusters of Lokiarchaeum ossiferum form dense assemblages that researchers can observe with relative ease, providing a practical window into their biology. Building on these observations, scientists are now prioritizing investigations into how these archæa engage in bacterial partnerships. Understanding such symbiotic relationships could illuminate how early cellular life transitioned toward greater complexity.
Researchers propose that the primitive eukaryotic cell may have emerged from a close, cooperative association between archæal and bacterial lineages roughly two billion years ago. If the ongoing work confirms this scenario, it would illuminate the origins of the cell nucleus and the emergence of multicellular organisms. The pursuit involves tracing the genetic and structural changes that accompanied that ancient symbiosis, offering a more detailed narrative of how the core features of eukaryotic cells came to be. The ongoing exploration of Asgard archæa and their bacterial partners thus holds the promise of filling gaps in our understanding of early evolutionary history and the transitions that led to complex life on Earth. [Citation: University of Vienna]