genome diversity of pseudomonas aeruginosa pao1 laboratory strains pseudomonas aeruginosa pao1 is the most commonly used strain for research on this ubiquitous and metabolically versatile opportunistic pathogen strain pao1 a derivative of the original australian pao isolate has been distributed worldwide to laboratories and strain collections over decades discordant phenotypes of pao1 sublines have emerged taking the existing pao1uw genome sequence named after the university of washington which led the sequencing project as a blueprint the genome sequences of reference strains mpao1 and pao1dsm stored at the german collection for microorganisms and cell cultures dsmz were resolved by physical mapping and deep short read sequencingbysynthesis mpao1 has been the source of nearsaturation libraries of transposon insertion mutants and pao1dsm is identical in its speidpni restriction map with the original isolate the major genomic differences of mpao1 and pao1dsm in comparison to pao1uw are the lack of a large inversion a duplication of a mobile 12kb prophage region carrying a distinct integrase and protein phosphatases or kinases deletions of 3 to 1006 bp in size and at least 39 singlenucleotide substitutions 17 of which affect protein sequences the pao1 sublines differed in their ability to cope with nutrient limitation and their virulence in an acute murine airway infection model subline pao1dsm outnumbered the two other sublines in late stationary growth phase in conclusion p aeruginosa pao1 shows an ongoing microevolution of genotype and phenotype that jeopardizes the reproducibility of research highthroughput genome resequencing will resolve more cases and could become a proper quality control for strain collections