Lysogenic integration

Certain strains of Escherichia coli can be stimulated by irradiation with a moderate dose of ultraviolet (UV) light to stop normal growth and start producing bacteriophages that eventually lyse the bacterium. Bacteria of these so-called lysogenic strains carry the DNA of the phage integrated into their own... 

Figure 5.21 Consequences of infection by a temperate bacteriophage. The alternatives upon infection are integration of the virus DNA into the host DNA (lysogenization) or replication and release of mature virus (lysis). The lysogenic cell can also be induced to produce mature virus and lyse.

About half of the time when A infects a cell it adopts a dormant lysogenic state in which the virus is linearly integrated into the host genome. This state is maintained by moderate amounts of the A-encoded cl repressor. The cl repressor prevents the lytic cycle from developing by inhibiting two promoters the PL promoter for early leftward transcription and PR the promoter for early rightward transcrip-... 

Figure 6.14. Alternative Infection Modes For A, phage. Lambda phage can multiply within a host and lyse it (lytic pathway), or its DNA can become integrated into the host genome (lysogenic pathway), where it is dormant until activated. 

Finally, another potential interplay between UVR and viruses occurs when they coexist with their host in a type of mutualistic relationship, where the nucleic acid of the virus is integrated in the genome of the host and is replicated with it (lysogenic state). Ultraviolet C radiation produced by germicidal lamps (max. at 254 nm) has normally been used, among other stressors, to induce the shift from lysogenic to lytic state in a complex mechanism involving the DNA repair SOS system of the host [93]. However, natural or simulated solar UVR seems not to be very efficient in this process [94,95]. 

Viral particles adsorb onto the surface of the bacterial cell and the viral genome is injected (infection). If the virus enters the lytic phase, the machinery of the host cell is directed toward the production and release of new viral particles. If the virus enters the lysogenic phase, the viral genome is integrated into the host cell DNA and may enter the lytic phase at a later time. 

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