The induction of Pl phage in E. coli thy-(Pl)

This investigation has shown that analogs of thymine induced Pl phage from E. coli C thy-3284. The Pl phage was induced by the antibiotic mitomycin C and thymine starvation. The induction of Pl phage from strain C-328 by uracil derivatives indicates that direct interference with DNA synthesis is not necessary for Pl prophage induction. UV irradiation, which caused phage induction and lysis in the lambda system, did not induce the Pl phage from C-328. This suggests a difference between the two phage systems. Inhibition of protein synthesis by chloroamphenicol did not induce Pl phage from C-328. An alteration in certain physical conditions, pH and osmotic pressure failed to induce Pl phage. When E. coli C thy-3284 (Pl) was incubated at 45°C, a bi- modal growth response was observed. The significance of this bimodal response was associated with the presence of two phage types: a thermoinducible and non-thermoinducible Pl phage in the culture of C-328. It was shown that E. coli C thy-3284 (Pl) was lysogenized by two phage types, such that some cells were lysogenized by the thermoinducible phage while others were lysogenized by the non-thermoinducible phage. It is suggested that one phage type was probably a mutant of the parent phage.