A Mutant of Escherichia coli That Is Lysogenized with High Frequency

A bacterium infected with the temperate bacteriophage lambda often gives rise to a lysogenic clone (Lwoff, 1953). Lysogeny may result when a sufficient level of repressor protein is established before an irreversible commitment to lytic growth is made (Jacob, 1960; Jacob and Campbell, 1959; Signer, 1970). The early events in the establishment of repression are not clearly defined, although several models outlining the process exist (Eisen et al., 1968; Oppenheim et al., 1970). Most models, however, ascribe the control of lysogenization wholly to the bacteriophage. Results presented below show that the host is involved too. Indeed, dependence on cellular metabolic conditions has been known for a long time. We describe here the isolation and properties of a mutant lysogenized by λ at frequencies approaching 100%. Furthermore the c III function of λ is not required for the establishment of lysogeny in the mutant. ISOLATION OF MUTANTS A log phase culture of Escherichia coli UC4185 (W3110 ser − trp − leu − ilv − lys − str r F − ) was mutagenized by N -methyl- N ′-nitro- N -nitrosoguanidine (NG) according to the method of Adelberg et al. (1965) and plated on tryptone agar plates. Individual colonies were picked and each was grown up in 1.0 ml tryptone broth at 37°C to stationary phase. These cultures were streaked onto tryptone agar plates and spot-tested with λc + , c II, and c III. Of 1100 mutagenized colonies, one gave turbid-centered plaques with c III (and λc + ). Lambda c II produced clear plaques, as did c I and vir. We named this bacterial mutant hfl- 1. CHARACTERIZATION OF THE MUTANT Table 1 shows...