title: Genome reduction of the aphid endosymbiont Buchnera aphidicola in a recent evolutionary time scale.
abstract: Genome reduction, a typical feature of symbiotic bacteria, was analyzed in the last stages of evolution of Buchnera aphidicola, the primary aphid endosymbiont, in two neutrally evolving regions: the pseudogene cmk and an intergenic region. These two regions were examined in endosymbionts from several lineages of their aphid host Rhopalosiphum padi, and different species of the same genus, whose divergence times ranged from 0.62 to 19.51 million years. Estimates of nucleotide substitution rates were between 4.3 and 6.7x10(-9) substitution/site/year, with G or C nucleotides being substituted around four times more frequently than A or T. Two different types of indel events were detected, of which many were small (1-10 nt) but one was large (about 200 nucleotides). With respect to the large one and considering the proportion and size of the deletions and insertions, the reduction rate was 1.3x10(-8) lost nucleotides/site/year. We propose a stepwise scenario for the last stages of evolution in B. aphidicola: together with a very slow and gradual degradation, considerable indels would punctually emerge. The only restriction to large deletion fixation is that the lost fragment does not contain essential genes.
authors.affiliation: Institut Cavanilles de Biodiversitat i Biologia Evolutiva and Departament de Genètica, Universitat de València, Apartat 22085, 46071 Valencia, Spain.
authors.forename: Laura
authors.initials: L
authors.lastname: Gómez-Valero
authors.forename: Francisco J
authors.initials: FJ
authors.lastname: Silva
authors.forename: Jean
authors.initials: J
authors.lastname: Christophe Simon
authors.forename: Amparo
authors.initials: A
authors.lastname: Latorre
mesh_terms: D000818:Animals; D001042:Aphids / Q000382:microbiology*; D001483:Base Sequence; D020635:Buchnera / Q000235:genetics*; D002138:Calibration; D004272:DNA, Mitochondrial / Q000235:genetics; D019143:Evolution, Molecular; D016680:Genome, Bacterial; D005843:Geography; D006239:Haplotypes; D009154:Mutation / Q000235:genetics; D009711:Nucleotides / Q000235:genetics; D010802:Phylogeny; D013559:Symbiosis / Q000235:genetics*; D013997:Time Factors
chemical_list: D004272:DNA, Mitochondrial; D009711:Nucleotides