Multiplication of bacteriophage P1 mutants in Shigella dysenteriae strain Sh(P1).

From bacteriophage P1, 10 mutants (P1cl) were isolated which are impaired in their ability to lysogenize Shigella dysenteriae Sh and which fail to make plaques when plated on Sh(P1). When Sh(P1) is infected with P1cl, a considerable proportion of the infected cells is converted into infectious centers, which eventually release P1cl but not P1. This phage release occurs over a period of several hours, during which a manyfold multiplication of infectious centers takes place. In the course of this multiplication, surviving bacteria, lysogenic for P1 only, are produced by segregation. At high multiplicity of infection, Sh(P1) are killed without producing any phage.