community members in deep-sea sediments
(Fig. 1) (33, 67). In contrast, Thorarchaeota and
Heimdallarchaeota (Fig. 1) seem to represent rare
members of sediment microbial communities (13).
Currently identified Odinarchaeota were found
in sediments of hot springs or hydrothermal vent
systems with temperatures ranging from about
60° to 70°C. Both Thor- and Lokiarchaeota encode
key enzymes of the WLP and may be capable
of acetogenesis (28, 68). Furthermore, these ge-
nomes show the potential for heterotrophic growth,
suggesting that they are also able to use the WLP
as electron acceptor during fermentation of or-
ganic substrates (28). Interestingly, the genetic
repertoire for the WLP appears to be absent from
genomic bins of Odin- and Heimdallarchaeota
(Fig. 3). Prospective analyses of the metabolic
features of Asgard archaea will certainly reveal a
more detailed picture of their functional potential
and ecological role.
DPANN superphylum and Altiarchaea
The DPANN superphylum represents a phylogenetically diverse archaeal superphylum that
Spang et al., Science 357, eaaf3883 (2017) 11 August 2017 4 of 10
Box 1. Glossary box.
AAG: Archaea of the ancient archaeal group. Heimdallarchaeota include lineages previously assigned to AAG.
Amo: Ammonia monooxygenase (Box 2).
ANME: A paraphyletic group of anaerobic methane-oxidizing euryarchaeota (Box 2).
AOA: Ammonia-oxidizing archaea (Box 2).
AOM: Anaerobic oxidation of methane (Box 2).
ARMAN: Archaeal Richmond Mine acidophilic nanoorganisms (Fig. 1).
Autotrophy: Ability of an organism to produce complex organic compounds from inorganic compounds such as CO2.
Chemolithotrophy: Ability to conserve energy from the oxidation of inorganic compounds.
Chemoorganotrophy: Use of organic substrates for energy conservation.
Clade: Group of organisms that includes a common ancestor and all its descendants.
Contigs: Contiguous stretches of DNA of different length obtained upon assembly of sequence reads. These generally represent subregions of
the genomic DNA of an organism.
DHVE: Refers to deep-sea hydrothermal vent euryarchaeota (Fig. 1).
DPANN: A proposed archaeal superphylum comprising Diapherotrites, Parvarchaeota, Aenigmarchaeota, Nanohaloarchaeota, and Nanoarchaeota.
More recently, additional candidate phyla such as Woesearchaeota, Pacearchaeota, and Micrarchaeota and possibly the Altiarchaeota were
suggested to be part of this group.
DSEG: Refers to deep-sea euryarchaeotal group (Fig. 1).
Environmental surveys: Profiling of microbial community composition via isolation of total nucleic acids from environmental samples and subsequent
sequencing, amplification, and analysis of 16S and 18S rRNA genes. Amplification is based on polymerase chain reactions by using primer sequences
that target conserved regions of 16S/18S rRNA genes.
Genomic bin: Composite genome comprising metagenomic contigs that are inferred to be derived from the same genome or species; also referred to as
metagenome-assembled genome (MAG).
Halophile: An organism that is dependent on high sodium chloride concentrations for growth and survival. Adaptation to salt content varies
between organisms (ranges from 0.3 to more than 5 M).
Heterotrophy: The requirement of complex organic compounds as source for cellular carbon.
Horizontal gene transfer (HGT): The lateral acquisition of genetic material from cells other than the parent cell, as opposed to vertical
transmission from parent to offspring.
Hyperthermophile: An organism that is adapted to temperatures above 80°C.
LACA: Last archaeal common ancestor.
MBG-B: Archaea of the marine benthic group B (also DSAG), now known as Lokiarchaeota (Fig. 1).
MBG-D: Archaea of the marine benthic group D (Fig. 1).
Mcr: Methyl–coenzyme M reductase (Box 2).
MG-II and MG-III: Two distinct marine groups belonging to the Euryarchaeota (Fig. 1). MG-II archaea are now referred to as Thalassoarchaea.
MCG: Archaea of the Miscellaneous Crenarchaeotal Group, now referred to as Bathyarchaeota (Fig. 1).
Metagenomic binning: The clustering of metagenomics contigs into taxonomic bins based on similarities in nucleotide composition profiles
and/or read coverage.
MSBL1: Archaea of the Mediterranean Sea Brine Lakes 1 group (Fig. 1).
Mesophile: An organism that thrives best at moderate temperatures between 20° and 45°C.
Metagenomics: The generation of DNA sequence data directly from environmental samples.
Methane seep: Locations at the seafloor that are characterized by the release of hydrocarbons dominated by methane.
Methylotrophy: A metabolic strategy in which organisms use organic compounds without C–C bonds as electron donors and carbon sources.
Monophyletic group: A set of organisms, which forms a clade and thus shares a common ancestor and includes all of its descendants.
Paraphyletic group: A set of organisms, which forms a clade and shares a common ancestor but does not include all of its descendant lineages.
SA1: Refers to a group of euryarchaeota, originally detected in brine-seawater interface samples from Shaban Deep, Red Sea.
TACK: A proposed archaeal superphylum comprising Thaumarchaeota, Aigarchaeota, Crenarchaeota, and Korarchaeota, in addition to the
tentative phyla Geoarchaeota, Bathyarchaeota, and Verstraetearchaeota. TACK is also referred to as Proteoarchaeota.
Thermophile: Organisms that thrive best at temperatures between 45° and 80°C.
TMCG: Archaea from the terrestrial miscellaneous crenarchaeota group, now also referred to as Verstraetearchaeota (Fig. 1).
SAGMEG: Refers to the South-African Gold Mine Miscellaneous Euryarchaeal Group, now named Hadesarchaea (Fig. 1).
Syntrophy: A metabolic process in which the degradation of a substrate gets energetically favorable through the cooperation of two different
organisms—a product generated by one partner is consumed by the other partner.
WLP: Wood-Ljungdahl carbon fixation pathway (Box 2).
WSA2/Arc1: A group of archaea first identified in a clone library (“WSA”) from a methanogenic sulfate-reducing core (Fig. 1) and later detected in
an anaerobic sludge digester and described as Arc1; now referred to as Methanofastidiosa.