Evolution of the secondary symbiont "Candidatus serratia symbiotica" in aphid species of the subfamily lachninae

Abstract

Buchnera aphidicola BCc, the primary endosymbiont of the aphid Cinara cedri (subfamily Lachninae), is losing its symbiotic capacity and might be replaced by the coresident "Candidatus Serratia symbiotica." Phylogenetic and morphological analyses within the subfamily Lachninae indicate two different "Ca. Serratia symbiotica" lineages and support the longtime coevolution of both symbionts in C. cedri.

FIG. 1.

Maximum likelihood phylogeny. (A) B. aphidicola 16S rRNA gene. The outgroups are B. aphidicola from Acyrthosiphon pisum and from Schizaphis graminum (GenBank accession numbers M27039 and NC_004061, respectively). (B) “Ca. Serratia symbiotica” 16S rRNA gene. Free-living bacteria are Serratia plymuthica (AY394724), Serratia marcescens (AF124038), and the outgroups Escherichia coli (AB045731) and Serratia boydii (AY696681). (C) Gene atpD from some selected “Ca. Serratia symbiotica” spp. Free-living bacteria are S. marcescens (ABI21950) and the outgroups Erwinia carotovora (IP_052595) and Yersinia pseudotuberculosis (BX936398). Numbers in nodes indicate support values in the form of proportions of bootstrap pseudoreplicates and Bayesian a posteriori probabilities for the corresponding inner branch. Branches with support values higher than 55% are collapsed. See Table 1 for species information.

FIG. 2.

Electron microscopy of C. cedri (A) and C. tujafilina (B). Primary and secondary bacteriocytes harbor B. aphidicola (a) and “Ca. Serratia symbiotica” (b).