Relationships among diverse gamma-Proteobacteria, estimated from a region of the 16S rDNA gene. Within Blochmannia, taxa are labeled by the ant host from which the bacterial gene was amplified. These and other ant symbionts are noted in boldface. The phylogeny was estimated using Bayesian methods. The topology shown reflects the majority-rule consensus of post-burnin trees, and posterior probabilities are given at nodes. The results support the monophyly of known Blochmannia isolates and newly sampled Camponotini associates (posterior probability of 1.00), demonstrating for first time that Calomyrmex, Echinopla, and Opisthopsis possess bacterial associates that are members of the same clade as known Blochmannia strains. Blochmannia occurs within a large, diverse, and strictly-endosymbiotic group that includes a wide range of insect endosymbionts. Plagiolepis and Formica endosymbionts do not group with Blochmannia, showing independent origins of intracellular endosymbioses within ants.