Buchnera aphidicola str. Sg (Schizaphis graminum)

Buchnera aphidicola subsp. Cinara cedri is the primary endosymbiont of the aphid Cinara cedri. The aphid-Buchnera association has persisted for at least 160 million years and it is obligate for both partners. Its genome is composed of a 416380-base pair circular chromosome plus a 6045-base pair plasmid for leucine. This genome is ca. 200 kilobases smaller than the other Buchnera aphidicola genomes sequenced so far. Gene loss is the main cause of genome shrinkage and affects all functional categories, although not evenly. Gene losses affecting biosynthesis of nucleotides, cofactors, cell envelope and transport are particularly important. It is no longer able to synthesize tryptophan, it is unable to provide riboflavin to its host and lacks most of the transporters encoded by other B.aphidicola genomes. Buchnera aphidicola subsp. Cinara cedri could be undergoing a process of genome degradation and functional replacement by the coexisting secondary endosymbiont Serratia symbiotica. (EBI Integr8)