The evolution and diversification of Archaea is central to the history of life on Earth. Cultivation-independent approaches have revealed the existence of the DPANN archaea: a radiation of organisms with small cell and genome sizes. Currently, the placement of the various DPANN lineages and in turn the early evolution of metabolism and symbiosis are debated. Here, we reconstructed genomes of a thus far uncharacterized archaeal phylum-level lineage UAP2 (Candidatus Undinarchaeota). Comparative genomics revealed that members of the Undinarchaeota have small estimated genome sizes and, while potentially being able to conserve energy through fermentation, likely depend on partner organisms for the acquisition of vitamins, amino acids and other metabolites. In contrast to previous indications, our phylogenomic analyses robustly placed the Undinarchaeota as independent lineage between two major and highly supported clans of ‘DPANN’. Furthermore, our work suggests that DPANN archaea have exchanged core genes with their hosts by horizontal gene transfer, adding to the difficulty of placing DPANN in the tree of life (ToL). In several cases, this pattern is sufficiently dominant that known symbiont-host clades can be identified by inferring routes of HGT across the ToL. Together, our findings provide crucial insights into the origins and evolution of DPANN archaea and their hosts.
|Publication status||Published - 7 Aug 2020|