Discussion
A lysogenic bacteriophage is one that
Answer: C
Correct answer: integrates its genome into the host chromosome as a prophage
A lysogenic or temperate phage integrates its genome into the host chromosome as a prophage, where it is replicated passively along with the bacterial DNA and passed to every daughter cell. The host is then a lysogen. The contrast is with the lytic cycle, in which the phage replicates immediately, assembles new particles and lyses the cell. A temperate phage can follow either path, and the choice is governed by a genetic switch - in phage lambda, by the balance between the cI repressor maintaining lysogeny and the Cro protein promoting lysis. DNA damage activates the SOS response, which inactivates the repressor and induces the prophage into the lytic cycle - a sensible strategy, since a damaged host is a poor long-term home. Lysogeny has consequences beyond the phage. Lysogenic conversion gives the host new properties encoded by prophage genes, and the toxins of diphtheria, cholera, botulism and scarlet fever are all prophage-encoded.
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