Figure 7.

Correlation of bacterial lifestyle and general genome features for selected free-living bacteria and insect symbionts. The numbers of pseudogenes, genomic G+C content and average spacer length are displayed (for details, see Supplementary Table S4). Gammaproteobacterial obligate symbionts of insects share similar genome features and are clearly separated in this three-dimensional scatter plot. Signs for genome erosion can be observed in facultative symbionts to different degrees. The placement of ‘Candidatus Steffania adelgidicola' between these two groups suggests that ‘Candidatus S. adelgidicola' is an evolutionarily young symbiont the genome of which is in the process of size reduction. For comparison, ‘Candidatus Hodgkinia cicadicola', an alphaproteobacterial symbiont of cicadas is shown. Its genome is highly reduced but in contrast to the genomes of gammaproteobacterial insect symbionts shows a high G+C content.