A korarchaeal genome reveals insights into the evolution of the Archaea.
The candidate division Korarchaeota comprises a group of uncultivated microorganisms that, by their small subunit rRNA phylogeny, may have diverged early from the major archaeal phyla Crenarchaeota and Euryarchaeota. Here, we report the initial characterization of a member of the Korarchaeota with the proposed name, "Candidatus Korarchaeum cryptofilum," which exhibits an ultrathin filamentous morphology. To investigate possible ancestral relationships between deep-branching Korarchaeota and other phyla, we used whole-genome shotgun sequencing to construct a complete composite korarchaeal genome from enriched cells. The genome was assembled into a single contig 1.59 Mb in length with a G + C content of 49%. Of the 1,617 predicted protein-coding genes, 1,382 (85%) could be assigned to a revised set of archaeal Clusters of Orthologous Groups (COGs). The predicted gene functions suggest that the organism relies on a simple mode of peptide fermentation for carbon and energy and lacks the ability to synthesize de novo purines, CoA, and several other cofactors. Phylogenetic analyses based on conserved single genes and concatenated protein sequences positioned the korarchaeote as a deep archaeal lineage with an apparent affinity to the Crenarchaeota. However, the predicted gene content revealed that several conserved cellular systems, such as cell division, DNA replication, and tRNA maturation, resemble the counterparts in the Euryarchaeota. In light of the known composition of archaeal genomes, the Korarchaeota might have retained a set of cellular features that represents the ancestral archaeal form.
Lehrstuhl für Mikrobiologie und Archaeenzentrum, Universität Regensburg, D-93053 Regensburg, Germany.
James G
JG
Elkins
Mircea
M
Podar
David E
DE
Graham
Kira S
KS
Makarova
Yuri
Y
Wolf
Lennart
L
Randau
Brian P
BP
Hedlund
Céline
C
Brochier-Armanet
Victor
V
Kunin
Iain
I
Anderson
Alla
A
Lapidus
Eugene
E
Goltsman
Kerrie
K
Barry
Eugene V
EV
Koonin
Phil
P
Hugenholtz
Nikos
N
Kyrpides
Gerhard
G
Wanner
Paul
P
Richardson
Martin
M
Keller
Karl O
KO
Stetter
D005075:Biological Evolution; D002453:Cell Cycle; D004261:DNA Replication; D004734:Energy Metabolism; D019143:Evolution, Molecular; D020745:Genome, Archaeal / Q000235:genetics*; D010802:Phylogeny; D014176:Protein Biosynthesis; D017422:Sequence Analysis, DNA; D014158:Transcription, Genetic; D019615:Crenarchaeota / Q000166:cytology / Q000235:genetics* / Q000648:ultrastructure