Multiplication in Serratia of a bacteriophage originating from Escherichia coli: lysogenization and host-controlled variation.

Temperate bacteriophage P2, originally obtained from Escherichia coli strain Lisbonne, and usually grown on E. coli or Shigella strains, is also able to multiply in some Serratia strains. One of these has been shown to give stable lysogenic derivatives upon P2 infection. In passing from E. coli to Serratia and vice versa, P2 undergoes host-controlled variation. The base ratio in the DNA of the Serratia strain used is typical of Serratia strains (59% GC content) whereas that of P2 DNA (50% GC content) is like that of E. coli DNA, even after the phage has been grown in the Serratia host. Serratia bacteria lysogenic for P2 do not seem to contain numerous P2 DNA equivalents. The accidental formation of identical base pair sequences in DNA's of similar or different base ratios is discussed in the appendix.