P1 phage

P1 is a temperate bacteriophage (phage). Temperate phage, such as P1, have the ability to exist within the bacterial cell they infect in two different ways. In lysogeny, PI can exist within a bacterial cell as a prophage in that it exists by replicating with the host chromosome and does not cause cell death. Alternatively, in its lytic phase, P1 can promote cell lysis during growth resulting in host cell death. During lysogeny new phage particles are not produced. In contrast, during lytic growth many new phage particles are assembled and released from the cell. By alternating between these two modes of infection, Pl can survive during extreme nutritional conditions that may be imposed upon the bacterial host in which it exists.

A unique feature of phage PI is that during lysogeny its genome is not incorporated into the bacterial chromosome as is commonly observed during lysogeny of other bacteriophage. Instead, Pl exists independently within the bacterial cell, much like a plasmid would. P1 replicates as a 90 kilobase (kb) plasmid in the lysogenic state and is partitioned equally into two new daughter cells during normal cell division