Lysogeny

Lysogeny is a temperate bacteriophage life cycle in which the phage genome is integrated into a bacterial host’s chromosome or maintained as a stable plasmid, and the phage remains largely dormant rather than producing new virions. In this lysogenic state, the bacterial cell, called a lysogen, divides with the prophage replicated along with its chromosome.

During lysogeny, the phage genome is integrated at specific attachment sites by phage-encoded integrase. The prophage is usually kept in check by a phage-encoded repressor protein, which prevents expression of lytic genes and also provides immunity to superinfection by the same phage. The prophage is replicated with the host genome and does not typically kill the host.

Lysogeny is not permanent. Environmental stress or DNA damage can lead to induction, a switch to the lytic cycle. In response to such signals, host DNA damage responses (for example, RecA-mediated cleavage of the phage repressor) can release repression, excise the prophage, replicate it, assemble new virions, and cause host cell lysis to release phage particles.

Prophages can influence bacterial traits through lysogenic conversion, where new genes carried by the prophage alter host phenotype. This includes virulence factors such as the diphtheria toxin in Corynebacterium diphtheriae and cholera toxin genes in Vibrio cholerae, as well as other traits that can affect fitness and ecological interactions. Lysogeny also enables horizontal gene transfer via specialized transduction.

Lysogeny is common among bacteriophages and contributes to genetic diversity, evolution, and the modulation of bacterial populations.