Bacteriophages, particularly lysogenic phages, play a crucial role in viral infections of bacteria. These temperate phages can follow two distinct pathways upon entering a host cell. The first pathway leads to the lytic cycle, where new phages are produced, resulting in the destruction of the host cell. The second pathway involves the integration of the phage DNA into the host's chromosome, forming a structure known as a prophage.
The lysogenic cycle, or lysogeny, is characterized by the silent replication of the prophage within the bacterial cell, referred to as a lysogen. During this cycle, the prophage remains inactive, yet it replicates alongside the host's DNA during cell division. Consequently, all progeny of the lysogen inherit the prophage, ensuring its transmission to future generations of bacteria.
In the lysogenic cycle, the initial steps include the attachment of the bacteriophage to the bacterial cell and the injection of its genome. Following this, the phage DNA can either integrate into the host chromosome or proceed to the lytic cycle. The integration step is critical, as it establishes the prophage within the bacterial genome. As the lysogen replicates, the prophage is also duplicated, leading to a population of cells that all contain the integrated phage DNA.
Under certain conditions, the prophage can excise itself from the host chromosome, a process facilitated by viral enzymes. This excision allows the lysogenic cycle to transition back into the lytic cycle, where the production of new phages can commence, ultimately leading to the lysis of the host cell and a productive infection.
Understanding the dynamics of lysogenic phage infections is essential, as it highlights the complex interactions between viruses and their bacterial hosts, illustrating how viral DNA can persist within bacterial populations and influence their genetic makeup.
