Pseudomonas bacteriophage contains an inner body in its capsid

Electron microscopical examination of the new virulent bacteriophage [Formula: see text], specific for Pseudomonas aeruginosa, has revealed an unusual structure in its capsid. In the center of the phage head is a cylinder of low electron density ("inner body"), surrounded by fibrous material which is packed around the inner body in a spoollike manner. The inner body itself has a springlike appearance. These structures disappear after adsorption of phage particles to bacteria. Various morphological forms, which can be interpreted as intermediate steps in [Formula: see text] DNA condensation, have been seen in ultrathin sections of [Formula: see text]-infected cells.