Data from: Rapid evolution of microbe-mediated protection against pathogens in a worm host

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.