title: Complex archaea that bridge the gap between prokaryotes and eukaryotes.
abstract: The origin of the eukaryotic cell remains one of the most contentious puzzles in modern biology. Recent studies have provided support for the emergence of the eukaryotic host cell from within the archaeal domain of life, but the identity and nature of the putative archaeal ancestor remain a subject of debate. Here we describe the discovery of 'Lokiarchaeota', a novel candidate archaeal phylum, which forms a monophyletic group with eukaryotes in phylogenomic analyses, and whose genomes encode an expanded repertoire of eukaryotic signature proteins that are suggestive of sophisticated membrane remodelling capabilities. Our results provide strong support for hypotheses in which the eukaryotic host evolved from a bona fide archaeon, and demonstrate that many components that underpin eukaryote-specific features were already present in that ancestor. This provided the host with a rich genomic 'starter-kit' to support the increase in the cellular and genomic complexity that is characteristic of eukaryotes.
authors.affiliation: Department of Cell and Molecular Biology, Science for Life Laboratory, Uppsala University, SE-75123 Uppsala, Sweden.
authors.forename: Anja
authors.initials: A
authors.lastname: Spang
authors.affiliation: Department of Cell and Molecular Biology, Science for Life Laboratory, Uppsala University, SE-75123 Uppsala, Sweden.
authors.forename: Jimmy H
authors.initials: JH
authors.lastname: Saw
authors.affiliation: Department of Biology, Centre for Geobiology, University of Bergen, N-5020 Bergen, Norway.
authors.forename: Steffen L
authors.initials: SL
authors.lastname: Jørgensen
authors.affiliation: Department of Cell and Molecular Biology, Science for Life Laboratory, Uppsala University, SE-75123 Uppsala, Sweden.
authors.forename: Katarzyna
authors.initials: K
authors.lastname: Zaremba-Niedzwiedzka
authors.affiliation: Department of Cell and Molecular Biology, Science for Life Laboratory, Uppsala University, SE-75123 Uppsala, Sweden.
authors.forename: Joran
authors.initials: J
authors.lastname: Martijn
authors.affiliation: Department of Cell and Molecular Biology, Science for Life Laboratory, Uppsala University, SE-75123 Uppsala, Sweden.
authors.forename: Anders E
authors.initials: AE
authors.lastname: Lind
authors.affiliation: Department of Cell and Molecular Biology, Science for Life Laboratory, Uppsala University, SE-75123 Uppsala, Sweden.
authors.forename: Roel
authors.initials: R
authors.lastname: van Eijk
authors.affiliation: Department of Biology, Centre for Geobiology, University of Bergen, N-5020 Bergen, Norway.|Division of Archaea Biology and Ecogenomics, Department of Ecogenomics and Systems Biology, University of Vienna, A-1090 Vienna, Austria.
authors.forename: Christa
authors.initials: C
authors.lastname: Schleper
authors.affiliation: Department of Cell and Molecular Biology, Science for Life Laboratory, Uppsala University, SE-75123 Uppsala, Sweden.|Department of Medical Biochemistry and Microbiology, Uppsala University, SE-75123 Uppsala, Sweden.
authors.forename: Lionel
authors.initials: L
authors.lastname: Guy
authors.affiliation: Department of Cell and Molecular Biology, Science for Life Laboratory, Uppsala University, SE-75123 Uppsala, Sweden.
authors.forename: Thijs J G
authors.initials: TJG
authors.lastname: Ettema
mesh_terms: D008841:Actin Cytoskeleton / Q000378:metabolism; D000199:Actins / Q000235:genetics / Q000378:metabolism; D001105:Archaea / Q000145:classification* / Q000235:genetics / Q000378:metabolism; D001110:Arctic Regions; D056827:Endosomal Sorting Complexes Required for Transport / Q000235:genetics / Q000378:metabolism; D056890:Eukaryota / Q000145:classification* / Q000235:genetics / Q000378:metabolism; D005057:Eukaryotic Cells / Q000145:classification / Q000378:metabolism; D019143:Evolution, Molecular; D060086:Hydrothermal Vents / Q000382:microbiology*; D054892:Metagenome / Q000235:genetics; D008969:Molecular Sequence Data; D020559:Monomeric GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism; D010802:Phylogeny; D011387:Prokaryotic Cells / Q000145:classification*; D020543:Proteome / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism
chemical_list: D000199:Actins; D056827:Endosomal Sorting Complexes Required for Transport; D020543:Proteome; D020559:Monomeric GTP-Binding Proteins