Phylogenetic trees of 16S rRNA gene sequences of the bacteria cultured in insect cells in this study (underlined). (a) Phylogenetic position in the γ-proteobacteria (1,480-nt gene fragments); (b) sequence diversity relative to known U-type and T-type symbionts (635-nt gene fragments). The bootstrap percentages at the nodes were calculated by the neighbor-joining and maximum-likelihood methods. GenBank accession numbers, bacterial species or “informal” names, and (in parentheses) the relevant insect hosts (where relevant) are indicated. PABS, pea aphid Bemisia symbiont; PAUS, pea aphid U-type symbiont; PASS, pea aphid secondary symbiont.