title: 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.
abstract: Both bacterial symbionts and pathogens rely on their host-sensing mechanisms to activate the biosynthetic pathways necessary for their invasion into host cells. The Gram-negative bacterium Sinorhizobium meliloti relies on its RSI (ExoR-ExoS-ChvI) Invasion Switch to turn on the production of succinoglycan, an exopolysaccharide required for its host invasion. Recent whole-genome sequencing efforts have uncovered putative components of RSI-like invasion switches in many other symbiotic and pathogenic bacteria. To explore the possibility of the existence of a common invasion switch, we have conducted a phylogenomic survey of orthologous ExoR, ExoS, and ChvI tripartite sets in more than ninety proteobacterial genomes. Our analyses suggest that functional orthologs of the RSI invasion switch co-exist in Rhizobiales, an order characterized by numerous invasive species, but not in the order's close relatives. Phylogenomic analyses and reconstruction of orthologous sets of the three proteins in Alphaproteobacteria confirm Rhizobiales-specific gene synteny and congruent RSI evolutionary histories. Evolutionary analyses further revealed site-specific substitutions correlated specifically to either animal-bacteria or plant-bacteria associations. Lineage restricted conservation of any one specialized gene is in itself an indication of species adaptation. However, the orthologous phylogenetic co-occurrence of all interacting partners within this single signaling pathway strongly suggests that the development of the RSI switch was a key adaptive mechanism. The RSI invasion switch, originally found in S. meliloti, is a characteristic of the Rhizobiales, and potentially a conserved crucial activation step that may be targeted to control host invasion by pathogenic bacterial species.
authors: Biochemistry Program, The Graduate Center, City University of New York, New York, New York, United States of America.
authors: Mary Ellen
authors: ME
authors: Heavner
authors: Biological Sciences Department, Hunter College, City University of New York, New York, New York, United States of America.
authors: Wei-Gang
authors: WG
authors: Qiu
authors: Biochemistry Program, The Graduate Center, City University of New York, New York, New York, United States of America; Biological Sciences Department, Lehman College, City University of New York, Bronx, New York, United States of America.
authors: Hai-Ping
authors: HP
authors: Cheng
mesh_terms: D036002:ADP Ribose Transferases / Q000145:classification* / Q000235:genetics; D001426:Bacterial Proteins / Q000145:classification* / Q000235:genetics; D001427:Bacterial Toxins / Q000145:classification* / Q000235:genetics; D015964:Gene Expression Regulation, Bacterial; D016680:Genome, Bacterial; D054884:Host-Pathogen Interactions; D010802:Phylogeny; D010935:Plant Diseases / Q000382:microbiology*; D011135:Polysaccharides, Bacterial / Q000096:biosynthesis*; D016415:Sequence Alignment; D016962:Sinorhizobium meliloti / Q000235:genetics / Q000472:pathogenicity*; D014157:Transcription Factors / Q000145:classification* / Q000235:genetics
chemical_list: D001426:Bacterial Proteins; D001427:Bacterial Toxins; D011135:Polysaccharides, Bacterial; D014157:Transcription Factors; C083719:chvI protein, Bacteria; C056779:succinoglycan; D036002:ADP Ribose Transferases; C444820:exoenzyme S