title: The impact of phages on interspecific competition in experimental populations of bacteria.
abstract: BACKGROUND
  Phages are thought to play a crucial role in the maintenance of diversity in natural bacterial communities. Theory suggests that phages impose density dependent regulation on bacterial populations, preventing competitive dominants from excluding less competitive species. To test this, we constructed experimental communities containing two bacterial species (Pseudomonas fluorescens and Pseudomonas aeruginosa) and their phage parasites. Communities were propagated at two environmental temperatures that reversed the outcome of competition in the absence of phage.
  
  
  RESULTS
  The evenness of coexistence was enhanced in the presence of a phage infecting the superior competitor and in the presence of phage infecting both competitors. This occurred because phage altered the balance of competitive interactions through reductions in density of the superior competitor, allowing concomitant increases in density of the weaker competitor. However, even coexistence was not equally stable at the two environmental temperatures.
  
  
  CONCLUSIONS
  Phage can alter competitive interactions between bacterial species in a way that is consistent with the maintenance of coexistence. However, the stability of coexistence is likely to depend upon the nature of the constituent bacteria-bacteriophage interactions and environmental conditions.
authors.affiliation: Department of Plant Sciences, University of Oxford, Oxford, OX1 3RB, UK. michael.brockhurst@liv.ac.uk
authors.forename: Michael A
authors.initials: MA
authors.lastname: Brockhurst
authors.forename: Andrew
authors.initials: A
authors.lastname: Fenton
authors.forename: Barrie
authors.initials: B
authors.lastname: Roulston
authors.forename: Paul B
authors.initials: PB
authors.lastname: Rainey
mesh_terms: D017753:Ecosystem; D006790:Host-Parasite Interactions; D008954:Models, Biological; D017105:Pseudomonas Phages / Q000502:physiology*; D011550:Pseudomonas aeruginosa / Q000254:growth & development* / Q000821:virology; D011551:Pseudomonas fluorescens / Q000254:growth & development* / Q000821:virology; D012641:Selection, Genetic