Microbial symbioses are essential for the normal development and growth of animals1,2,3. Often, symbionts must be acquired from the environment during each generation, and identification of the relevant symbiotic partner against a myriad of unwanted relationships is a formidable task4. Although examples of this specificity are well-documented, the genetic mechanisms governing it are poorly characterized5. Here we show that the two-component sensor kinase RscS is necessary and sufficient for conferring efficient colonization of Euprymna scolopes squid by bioluminescent Vibrio fischeri from the North Pacific Ocean. In the squid symbiont V. fischeri ES114, RscS controls light-organ colonization by inducing the Syp exopolysaccharide, a mediator of biofilm formation during initial infection. A genome-level comparison revealed that rscS, although present in squid symbionts, is absent from the fish symbiont V. fischeri MJ11. We found that heterologous expression of RscS in strain MJ11 conferred the ability to colonize E. scolopes in a manner comparable to that of natural squid isolates. Furthermore, phylogenetic analyses support an important role for rscS in the evolution of the squid symbiosis. Our results demonstrate that a regulatory gene can alter the host range of animal-associated bacteria. We show that, by encoding a regulator and not an effector that interacts directly with the host, a single gene can contribute to the evolution of host specificity by switching ‘on’ pre-existing capabilities for interaction with animal tissue.
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The recA, mdh, katA and rscS sequence data from the additional strains described in the article are deposited in GenBank under accession numbers EU907941–EU908017; MJ11 genome data are deposited under accession numbers CP001133, CP001134 and CP001139.
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We thank: P. Dunlap for sharing bacterial strains; N. Perna, J. Glasner, K. Geszvain, D. Baum, J. Johnson, M. Sarmiento and S. Ferriera for technical assistance; A. Wier, N. Bekiares, R. Gates and the Hawaii Institute of Marine Biology for animal facilities and care; J. McCosker and the Steinhart Aquarium for access to fish specimens; M. McFall-Ngai, H. Goodrich-Blair, C. Brennan and J. Troll for discussions; and L. Proctor for project support. MJ11 genome sequencing was funded by the Gordon and Betty Moore Foundation Marine Microbial Genome Sequencing Project; E.G.R. and co-workers are funded by the National Institutes of Health–National Center for Research Resources and the National Science Foundation Division of Integrative Organismal Systems; E.V.S. is funded by a National Science Foundation CAREER Award; K.L.V. is funded by the National Institute of General Medical Sciences; M.J.M. is funded by a National Institute of General Medical Sciences National Research Service Award Postdoctoral Fellowship; M.S.W. is funded by a National Science Foundation Predoctoral Fellowship and a National Institutes of Health Molecular Biosciences Training Grant to the University of Wisconsin.
Author Contributions M.J.M. designed the experiments, performed all work not described below, and wrote the paper. M.S.W. conducted the phylogenetic studies. K.L.V. constructed plasmids and strains, and imaged biofilm phenotypes. M.J.M. planned and performed the genome assembly and analytics, and M.J.M., E.V.S. and E.G.R. analysed the bioinformatics results.
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Mandel, M., Wollenberg, M., Stabb, E. et al. A single regulatory gene is sufficient to alter bacterial host range. Nature 458, 215–218 (2009). https://doi.org/10.1038/nature07660
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