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Background  During chronic lung infections of cystic fibrosis patients  Pseudomonas aeruginosa  populations undergo extensive evolutionary diversification. However, the selective drivers of this evolutionary process are poorly understood. To test the effects of temperate phages on diversification in  P. aeruginosa  biofilms we experimentally evolved populations of  P. aeruginosa  for approximately 240 generations in artificial sputum medium with or without a community of three temperate phages.    Results  Analysis of end-point populations using a suite of phenotypic tests revealed extensive phenotypic diversification within populations, but no significant differences between the populations evolved with or without phages. The most common phenotypic variant observed was loss of all three types of motility (swimming, swarming and twitching) and resistance to all three phages. Despite the absence of selective pressure, some members of the population evolved antibiotic resistance. The frequency of antibiotic resistant isolates varied according to population and the antibiotic tested. However, resistance to ceftazidime and tazobactam-piperacillin was observed more frequently than resistance to other antibiotics, and was associated with higher prevelence of isolates exhibiting a hypermutable phenotype and increased beta-lactamase production.    Conclusions  We observed considerable within-population phenotypic diversity in  P. aeruginosa  populations evolving in the artificial sputum medium biofilm model. Replicate populations evolved both in the presence and absence of phages converged upon similar sets of phenotypes. The evolved phenotypes, including antimicrobial resistance, were similar to those observed amongst clinical isolates from cystic fibrosis infections.    Electronic supplementary material  The online version of this article (doi:10.1186/s12866-016-0916-z) contains supplementary material, which is available to authorized users.

Evolutionary diversification of Pseudomonas aeruginosa in an artificial sputum model