Fig. 1

Distribution of Orthologous Groups (OGs) by the number of Chlamydia genomes that have them (the U-curve). The left and right peaks of the curve correspond to unique (singletons) and universally conserved (core) genes, respectively. The rest of the OGs form the periphery. Internal peaks are mainly formed by OGs specific to individual species or monophyletic groups of species. In particular, peak at 55 genomes (*) corresponds to genes specific to the clade comprised of C. abortus, C. psittaci, C. felis, C. caviae, and C. poikilothermis. Peaks at 143 (***) and 84 genomes (**), respectively, are formed by orthologous groups specific to two clades previously assigned to genera Chlamydia (C. trachomatis, C. muridarum, and C. suis) and Chlamydophila (all other species). The statistics of the pan-genome components (core, periphery, and singletons) is shown in the inset table. It includes the number of OGs in the component, the median protein length, the number of OGs containing genes that have known conserved protein domains (according to Pfam-A), and the number of OGs containing genes with Gene Ontology (GO) annotation