title: A genomic analysis of the archaeal system Ignicoccus hospitalis-Nanoarchaeum equitans.
abstract: BACKGROUND
  The relationship between the hyperthermophiles Ignicoccus hospitalis and Nanoarchaeum equitans is the only known example of a specific association between two species of Archaea. Little is known about the mechanisms that enable this relationship.
  
  
  RESULTS
  We sequenced the complete genome of I. hospitalis and found it to be the smallest among independent, free-living organisms. A comparative genomic reconstruction suggests that the I. hospitalis lineage has lost most of the genes associated with a heterotrophic metabolism that is characteristic of most of the Crenarchaeota. A streamlined genome is also suggested by a low frequency of paralogs and fragmentation of many operons. However, this process appears to be partially balanced by lateral gene transfer from archaeal and bacterial sources.
  
  
  CONCLUSIONS
  A combination of genomic and cellular features suggests highly efficient adaptation to the low energy yield of sulfur-hydrogen respiration and efficient inorganic carbon and nitrogen assimilation. Evidence of lateral gene exchange between N. equitans and I. hospitalis indicates that the relationship has impacted both genomes. This association is the simplest symbiotic system known to date and a unique model for studying mechanisms of interspecific relationships at the genomic and metabolic levels.
authors.affiliation: Biosciences Division, Oak Ridge National Laboratory, 1 Bethel Valley Rd, Oak Ridge, TN 37831, USA. podarm@ornl.gov
authors.forename: Mircea
authors.initials: M
authors.lastname: Podar
authors.forename: Iain
authors.initials: I
authors.lastname: Anderson
authors.forename: Kira S
authors.initials: KS
authors.lastname: Makarova
authors.forename: James G
authors.initials: JG
authors.lastname: Elkins
authors.forename: Natalia
authors.initials: N
authors.lastname: Ivanova
authors.forename: Mark A
authors.initials: MA
authors.lastname: Wall
authors.forename: Athanasios
authors.initials: A
authors.lastname: Lykidis
authors.forename: Kostantinos
authors.initials: K
authors.lastname: Mavromatis
authors.forename: Hui
authors.initials: H
authors.lastname: Sun
authors.forename: Matthew E
authors.initials: ME
authors.lastname: Hudson
authors.forename: Wenqiong
authors.initials: W
authors.lastname: Chen
authors.forename: Cosmin
authors.initials: C
authors.lastname: Deciu
authors.forename: Don
authors.initials: D
authors.lastname: Hutchison
authors.forename: Jonathan R
authors.initials: JR
authors.lastname: Eads
authors.forename: Abraham
authors.initials: A
authors.lastname: Anderson
authors.forename: Fillipe
authors.initials: F
authors.lastname: Fernandes
authors.forename: Ernest
authors.initials: E
authors.lastname: Szeto
authors.forename: Alla
authors.initials: A
authors.lastname: Lapidus
authors.forename: Nikos C
authors.initials: NC
authors.lastname: Kyrpides
authors.forename: Milton H
authors.initials: MH
authors.lastname: Saier
authors.forename: Paul M
authors.initials: PM
authors.lastname: Richardson
authors.forename: Reinhard
authors.initials: R
authors.lastname: Rachel
authors.forename: Harald
authors.initials: H
authors.lastname: Huber
authors.forename: Jonathan A
authors.initials: JA
authors.lastname: Eisen
authors.forename: Eugene V
authors.initials: EV
authors.lastname: Koonin
authors.forename: Martin
authors.initials: M
authors.lastname: Keller
authors.forename: Karl O
authors.initials: KO
authors.lastname: Stetter
mesh_terms: D001692:Biological Transport; D019620:Desulfurococcaceae / Q000235:genetics* / Q000502:physiology; D004734:Energy Metabolism; D022761:Gene Transfer, Horizontal; D020745:Genome, Archaeal; D046588:Nanoarchaeota / Q000235:genetics* / Q000502:physiology; D010802:Phylogeny; D013559:Symbiosis