title: Reductive genome evolution in Buchnera aphidicola.
abstract: We have sequenced the genome of the intracellular symbiont Buchnera aphidicola from the aphid Baizongia pistacea. This strain diverged 80-150 million years ago from the common ancestor of two previously sequenced Buchnera strains. Here, a field-collected, nonclonal sample of insects was used as source material for laboratory procedures. As a consequence, the genome assembly unveiled intrapopulational variation, consisting of approximately 1,200 polymorphic sites. Comparison of the 618-kb (kbp) genome with the two other Buchnera genomes revealed a nearly perfect gene-order conservation, indicating that the onset of genomic stasis coincided closely with establishment of the symbiosis with aphids, approximately 200 million years ago. Extensive genome reduction also predates the synchronous diversification of Buchnera and its host; but, at a slower rate, gene loss continues among the extant lineages. A computational study of protein folding predicts that proteins in Buchnera, as well as proteins of other intracellular bacteria, are generally characterized by smaller folding efficiency compared with proteins of free living bacteria. These and other degenerative genomic features are discussed in light of compensatory processes and theoretical predictions on the long-term evolutionary fate of symbionts like Buchnera.
authors.affiliation: Centro de Astrobiologia, Instituto Nacional de Técnica Aeroespacial-Consejo Superior de Investigaciones Cientificas, Carretera de Ajalvir kilómetro 4, 28850 Torrejón de Ardoz, Madrid, Spain.
authors.forename: Roeland C H J
authors.initials: RC
authors.lastname: van Ham
authors.forename: Judith
authors.initials: J
authors.lastname: Kamerbeek
authors.forename: Carmen
authors.initials: C
authors.lastname: Palacios
authors.forename: Carolina
authors.initials: C
authors.lastname: Rausell
authors.forename: Federico
authors.initials: F
authors.lastname: Abascal
authors.forename: Ugo
authors.initials: U
authors.lastname: Bastolla
authors.forename: Jose M
authors.initials: JM
authors.lastname: Fernández
authors.forename: Luis
authors.initials: L
authors.lastname: Jiménez
authors.forename: Marina
authors.initials: M
authors.lastname: Postigo
authors.forename: Francisco J
authors.initials: FJ
authors.lastname: Silva
authors.forename: Javier
authors.initials: J
authors.lastname: Tamames
authors.forename: Enrique
authors.initials: E
authors.lastname: Viguera
authors.forename: Amparo
authors.initials: A
authors.lastname: Latorre
authors.forename: Alfonso
authors.initials: A
authors.lastname: Valencia
authors.forename: Federico
authors.initials: F
authors.lastname: Morán
authors.forename: Andrés
authors.initials: A
authors.lastname: Moya
mesh_terms: D001483:Base Sequence; D005075:Biological Evolution; D020635:Buchnera / Q000235:genetics*; D004260:DNA Repair; D004261:DNA Replication; D014644:Genetic Variation; D016680:Genome, Bacterial; D008969:Molecular Sequence Data; D011995:Recombination, Genetic; D013559:Symbiosis