Evidence for the retraction of Pseudomonas aeruginosa RNA phage pili

The pilus retraction model suggests that RNA phage pili retract when virions adsorb to their sides. The particle nearest the base is pulled against the cell surface and stops further retraction. If one phage per pilus were adsorbed, a length reduction averaging 50% over a number of pili would be predicted due to adsorption at random points along them. Electron microscopy is used here to measure the lengths of polar pili of P. aeruginosa before and after RNA phage adsorption. 40–50% reductions are found and length distribution curves indicate that retraction has occurred.