Lysogen

A lysogen is a bacterium that contains a prophage, which is a viral genome integrated into the host cell's DNA or existing as a plasmid within the host bacterium. The bacterium is referred to as lysogenic because it has the potential to undergo lysis, releasing viral particles.

The process by which a bacterium becomes a lysogen is called lysogeny. It is a non-lytic viral life cycle exhibited by some bacteriophages (viruses that infect bacteria). During lysogeny, the bacteriophage DNA integrates into the bacterial chromosome or exists as a stable plasmid, becoming a prophage. The prophage replicates along with the host cell's DNA during normal cell division, and the host cell survives and continues to multiply.

The prophage state can persist for many generations. However, under certain conditions, such as exposure to UV radiation or chemicals, the prophage can excise itself from the host chromosome (or lose its plasmid form) and enter the lytic cycle. This process is called induction. Once the lytic cycle begins, the virus replicates within the host cell, leading to the production of new viral particles and eventual lysis (destruction) of the host cell, releasing the newly formed phages.

Lysogeny is a significant phenomenon in bacterial genetics and evolution. Prophages can carry genes that alter the phenotype of the host bacterium, a process known as lysogenic conversion. These genes can confer advantages such as toxin production, antibiotic resistance, or altered surface properties, contributing to bacterial virulence and adaptation.