The Evolutionary Cost of ‘Re-evolving’ Motility in Pseudomonas fluorescens ΔfleQ mutants

The bacterium makes a flagellum and a surfactant, called viscosin. Both enable efficient surface motility on semi-solid agar and over plant roots. FleQis the master regulator of flagella expression. FleQis a bacterial enhancer-binding protein (bEBP) that is necessary to activate the promoter bound to the σ54-RNA polymerase, and consequently allow the hierarchical expression of flagellargenes. Knockout of fleQsuppresses the ability to make a flagellum, but the bacterium can still slowly slide over viscosin. However, the bacterium cannot swim through semi-solid agar. We examined whether the fleQmutant (SBW25Q) can evolve swimming motility by experimental evolution