Large-scale phylogenomics reveals convergent genome evolution across repeated transitions to endosymbiosis in Enterobacterales

Symbiogenesis stands among the major transitions in the history of life on Earth. Over the past three decades, extensive research has focused on specific host-symbiont associations to investigate their genome evolution. However, the idiosyncratic sequence evolution of endosymbionts has made it challenging to establish a robust phylogenetic framework for identifying broad-scale evolutionary patterns. Here, we establish the first genome-scale phylogenomic resolution for the Enterobacterales order, encompassing both free-living and endosymbiont species, and provide an analysis of gene loss and acquisition dynamics at scale. By examining over 200 genomes, we show remarkable consistency in phenomena previously known from scattered observations: a spike in gene loss invariably accompanies the shift to endosymbiosis, followed by a slower but continuous rate of gene erosion; gene acquisition processes are reduced after the lifestyle shift. Furthermore, convergence in gene family loss across independent and distantly related symbiotic lineages is observed, with genes having conserved functions and evolving under strong constraints lost at lower rates. Our results unify scattered observations into a broad-scale view of the consequences of endosymbiont genome evolution and highlight the roles of gene essentiality and dispensability in shaping convergent evolutionary trajectories.