Lysogenic Induction

Abstract

Thus, the problem of the mechanism of induction is now close to its solution. (Lwoff 1966)

INDUCIBLE PROPHAGES
Most bacteria found in nature are lysogenic (Lwoff 1953). They carry the genome of a virus in a dormant state, which is then called a prophage. The term lysogenic derives from the ability of these bacteria to generate the lysis of related species. The fact that the supernatant of a culture of lysogenic bacteria (or lysogens) causes lysis of other bacteria implies two properties of the lysogenic state. (1) In a growing culture of a lysogen, some cells spontaneously release phage particles. (2) Lysogenic bacteria are constantly exposed to the released phage but are not themselves lysed; they are said to be immune. Released phage can be revealed by infection of other sensitive bacteria that serve as indicator.

In trying to understand spontaneous production of phage by lysogens, Lwoff et al. (1950) sought ways to increase phage production artifically. Their first success followed exposure of lysogenic Bacillus megaterium to UV light. The culture lysed en masse, liberating hundreds of phage per cell. Since vegetative growth of a virus had been generated from within the bacterium by some as yet unknown action of UV light, this process was called lysogenic induction.

Soon after the discovery of lysogenic induction in Bacillus, Escherichia coli K12 was found to carry prophage λ, a prophage also inducible by UV light (Weigle and Delbrück 1951). Since E. coli K12 lent itself to genetic analysis, phage λ immediately became...