title: Rapid evolution of microbe-mediated protection against pathogens in a worm host.
abstract: Microbes can defend their host against virulent infections, but direct evidence for the adaptive origin of microbe-mediated protection is lacking. Using experimental evolution of a novel, tripartite interaction, we demonstrate that mildly pathogenic bacteria (Enterococcus faecalis) living in worms (Caenorhabditis elegans) rapidly evolved to defend their animal hosts against infection by a more virulent pathogen (Staphylococcus aureus), crossing the parasitism-mutualism continuum. Host protection evolved in all six, independently selected populations in response to within-host bacterial interactions and without direct selection for host health. Microbe-mediated protection was also effective against a broad spectrum of pathogenic S. aureus isolates. Genomic analysis implied that the mechanistic basis for E. faecalis-mediated protection was through increased production of antimicrobial superoxide, which was confirmed by biochemical assays. Our results indicate that microbes living within a host may make the evolutionary transition to mutualism in response to pathogen attack, and that microbiome evolution warrants consideration as a driver of infection outcome.
authors.affiliation: Institute of Integrative Biology, University of Liverpool, Liverpool, UK.|Department of Zoology, University of Oxford, Oxford, UK.
authors.forename: Kayla C
authors.initials: KC
authors.lastname: King
authors.affiliation: Department of Biology, University of York, York, UK.
authors.forename: Michael A
authors.initials: MA
authors.lastname: Brockhurst
authors.affiliation: Institute of Integrative Biology, University of Liverpool, Liverpool, UK.
authors.forename: Olga
authors.initials: O
authors.lastname: Vasieva
authors.affiliation: Institute of Integrative Biology, University of Liverpool, Liverpool, UK.
authors.forename: Steve
authors.initials: S
authors.lastname: Paterson
authors.affiliation: Department of Zoology, University of Oxford, Oxford, UK.
authors.forename: Alex
authors.initials: A
authors.lastname: Betts
authors.affiliation: Department of Zoology, University of Oxford, Oxford, UK.
authors.forename: Suzanne A
authors.initials: SA
authors.lastname: Ford
authors.affiliation: Institute of Integrative Biology, University of Liverpool, Liverpool, UK.
authors.forename: Crystal L
authors.initials: CL
authors.lastname: Frost
authors.affiliation: Institute of Integrative Biology, University of Liverpool, Liverpool, UK.
authors.forename: Malcolm J
authors.initials: MJ
authors.lastname: Horsburgh
authors.affiliation: Institute of Integrative Biology, University of Liverpool, Liverpool, UK.
authors.forename: Sam
authors.initials: S
authors.lastname: Haldenby
authors.affiliation: Institute of Integrative Biology, University of Liverpool, Liverpool, UK.
authors.forename: Gregory Dd
authors.initials: GD
authors.lastname: Hurst
mesh_terms: D000818:Animals; D005075:Biological Evolution; D017173:Caenorhabditis elegans / Q000235:genetics / Q000382:microbiology*; D013293:Enterococcus faecalis / Q000235:genetics / Q000502:physiology*; D005260:Female; D064307:Microbiota; D013211:Staphylococcus aureus / Q000472:pathogenicity*; D013559:Symbiosis