title: Cooperation and virulence in acute Pseudomonas aeruginosa infections.
abstract: BACKGROUND
  Efficient host exploitation by parasites is frequently likely to depend on cooperative behaviour. Under these conditions, mixed-strain infections are predicted to show lower virulence (host mortality) than are single-clone infections, due to competition favouring non-contributing social 'cheats' whose presence will reduce within-host growth. We tested this hypothesis using the cooperative production of iron-scavenging siderophores by the pathogenic bacterium Pseudomonas aeruginosa in an insect host.
  
  
  RESULTS
  We found that infection by siderophore-producing bacteria (cooperators) results in more rapid host death than does infection by non-producers (cheats), and that mixtures of both result in intermediate levels of virulence. Within-host bacterial growth rates exhibited the same pattern. Crucially, cheats were more successful in mixed infections compared with single-clone infections, while the opposite was true of cooperators.
  
  
  CONCLUSIONS
  These data demonstrate that mixed clone infections can favour the evolution of social cheats, and thus decrease virulence when parasite growth is dependent on cooperative behaviours.
authors.affiliation: Department of Zoology, University of Oxford, South Parks Road, Oxford OX1 3PS, UK. freya.harrison@zoo.ox.ac.uk
authors.forename: Freya
authors.initials: F
authors.lastname: Harrison
authors.forename: Lucy E
authors.initials: LE
authors.lastname: Browning
authors.forename: Michiel
authors.initials: M
authors.lastname: Vos
authors.forename: Angus
authors.initials: A
authors.lastname: Buckling
mesh_terms: D000818:Animals; D005075:Biological Evolution; D003299:Cooperative Behavior; D006790:Host-Parasite Interactions; D009036:Moths / Q000382:microbiology*; D011550:Pseudomonas aeruginosa / Q000472:pathogenicity*; D014774:Virulence