Asgardarchaeota

Asgardarchaeota, commonly referred to as Asgard archaea, is a proposed superphylum within the domain Archaea that includes several lineages discovered in environmental DNA. The major described groups are Lokiarchaeota, Thorarchaeota, Odinarchaeota, and Heimdallarchaeota, named after figures from Norse mythology. The group was first described in 2015 from metagenome-assembled genomes recovered from deep-sea sediments and hydrothermal environments. The discovery attracted attention because Asgard archaeal genomes contain a suite of eukaryotic signature proteins, including components related to cytoskeletal structure and membrane trafficking, which raised the possibility that these organisms are closely related to the eukaryotic lineage and offered potential insights into the origin of eukaryotes.

Ecology and metabolism: Asgard archaea are known from diverse anaerobic environments, including marine sediments and hydrothermal systems. Most members are known only from genomic data, and cultivated representatives have not been widely reported; consequently metabolic capabilities are inferred from genomes and remain tentative. Analyses have suggested heterotrophic lifestyles with potential for complex organic matter processing and interactions with other microbes, but exact metabolisms vary by lineage.

Phylogeny and significance: The placement of eukaryotes within or alongside Asgard archaea remains a subject of debate in evolutionary biology. Some analyses propose a two-domain tree in which eukaryotes emerge from within the Asgard superphylum, while others support alternative scenarios. Ongoing sequencing continues to reveal greater diversity within Asgard archaea and challenges to simple branchings of the tree of life.

Notes: Asgard archaea are primarily known from genomic data, reflecting the challenges of cultivating these organisms and the evolving understanding of their evolutionary importance.