Phylogenetic Co-Occurrence of ExoR, ExoS, and ChvI, Components of the RSI Bacterial Invasion Switch, Suggests a Key Adaptive Mechanism Regulating the Transition between Free-Living and Host-Invading Phases in Rhizobiales.

摘要: Both bacterial symbionts and pathogens rely on their host-sensing mechanisms to activate the biosynthetic pathways necessary for invasion into host cells. The Gram-negative bacterium Sinorhizobium meliloti relies its RSI (ExoR-ExoS-ChvI) Invasion Switch turn production of succinoglycan, an exopolysaccharide required invasion. Recent whole-genome sequencing efforts have uncovered putative components RSI-like switches in many other symbiotic pathogenic bacteria. To explore possibility existence a common switch, we conducted phylogenomic survey orthologous ExoR, ExoS, ChvI tripartite sets more than ninety proteobacterial genomes. Our analyses suggest that functional orthologs switch co-exist Rhizobiales, order characterized by numerous invasive species, but not order’s close relatives. Phylogenomic reconstruction three proteins Alphaproteobacteria confirm Rhizobiales-specific gene synteny congruent evolutionary histories. Evolutionary further revealed site-specific substitutions correlated specifically either animal-bacteria or plant-bacteria associations. Lineage restricted conservation any one specialized is itself indication species adaptation. However, phylogenetic co-occurrence all interacting partners within this single signaling pathway strongly suggests development was key adaptive mechanism. originally found S. meliloti, characteristic potentially conserved crucial activation step may be targeted control species.