Copyright © by National Academy of Sciences.-- La versión original está disponible en http://www.pnas.org/.-- Supplementary material available at: http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=141039#supplementary-material-sec
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 ≈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, ≈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.
This work was supported
by Fondo Social Europeo, European Union; Fondo Social
Europeo para el Desarrollo Regional, European Union; Comunidad
Autónoma de Madrid, Spain; Comunidad Autónoma de València, Spain;
Instituto Nacional de Técnica Aeroespacial, Spain; and Ministerio de
Ciencia y Tecnología, Spain (Grants 2FD1997-1006 and BFM2000-
1383).
Peer reviewed