Construction and validation of a neutrally-marked strain of Pseudomonas fluorescens SBW25

Neutrally marked bacterial strains are useful in many experimental evolution and molecular ecology studies to assess the relative fitness of a given strain. Here we describe the construction and validation of a neutral marker for the model organism Pseudomonas fluorescens SBW25. The marked strain, called SBW25-lacZ, was created by integrating a promoterless ‘lacZ into the defective prophage locus of the SBW25 chromosome. Fitness assays conducted in various laboratory media and in planta revealed that the fitness levels of SBW25-lacZ were comparable with the wild-type ancestor.