Dombrowski, NinaWilliams, Tom A.Sun, JiaruiWoodcroft, B JLee, Jun-HoeMinh, Bui QuangRinke, ChristianSpang, Anja2022-02-242022-02-242041-1723http://hdl.handle.net/1885/261534The recently discovered DPANN archaea are a potentially deep-branching, monophyletic radiation of organisms with small cells and genomes. However, the monophyly and early emergence of the various DPANN clades and their role in life's evolution are debated. Here, we reconstructed and analysed genomes of an uncharacterized archaeal phylum (Candidatus Undinarchaeota), revealing that its members have small genomes and, while potentially being able to conserve energy through fermentation, likely depend on partner organisms for the acquisition of certain metabolites. Our phylogenomic analyses robustly place Undinarchaeota as an independent lineage between two highly supported 'DPANN' clans. Further, our analyses suggest that DPANN have exchanged core genes with their hosts, adding to the difficulty of placing DPANN in the tree of life. This pattern can be sufficiently dominant to allow identifying known symbiont-host clades based on routes of gene transfer. Together, our work provides insights into the origins and evolution of DPANN and their hosts.This work was supported by a grant of the Swedish Research Council (VR starting grant 2016-03559 to A.S.), the NWO-I foundation of the Netherlands Organization for Scientific Research (WISE fellowship to A.S.), and an Australian Research Council (ARC) Future Fellowship (FT170100213, awarded to C.R.). T.W. was supported by a Royal Society University Research Fellowship, B.W. was supported by the Australian Research Council Discovery Early Career Research Awards #DE160100248 and B.Q.M. was supported by a Chan-Zuckberg Initiative grant for Essential Open Source Software for Scienceapplication/pdfen-AU© The Author(s) 2020http://creativecommons.org/ licenses/by/4.0/202010.1038/s41467-020-17408-w2020-12-13Creative Commons Attribution 4.0 International License