A putative insect intracellular endosymbiont stem clade, within the Enterobacteriaceae, infered from phylogenetic analysis based on a heterogeneous model of DNA evolution

Insect intracellular symbiotic bacteria (intracellular endosymbionts, or en docytobionts) were positioned within the gamma3-Proteobacteria using a non- homogeneous model of DNA evolution, allowing for rate variability among sit es, for GC content heterogeneity among sequences, and applied to a maximum likelihood framework. Most of them were found to be closely related within the Enterobacteriaceae family, located between Proteus and Yersinia. These results suggest that such a bacterial group might possess several traits al lowing for insect infection and the stable establishment of symbiotic relat ionships and that this could represent a stem clade for numerous insect end ocytobionts. Based on the estimations of the equilibrium GC content and bra nch lengths in the phylogenetic tree, we have made comparisons of the relat ive ages of these different symbioses. (C) 2001 Academie des sciences/Editi ons scientifiques et medicales Elsevier SAS.