Temperate phages are those that have the ability to enter an inactive prophage stage. This type of phage is capable of establishing a lysogenic cycle of infection, in which the virus can remain dormant and incorporated into the host genome. These phage genomes may remain in the host genome as prophages for extended periods of time, before being activated and entering the lytic cycle.
The main feature that distinguishes temperate phages from lytic phages is their ability to form a prophage. When a temperate phage enters its host cell, it will use its DNA to integrate into the host genome. This creates a prophage, which is a viral genome that is inactive and stably incorporated into the host chromosome. The prophage is inactive during this stage, as the host cell will not express the viral genes.
The prophage can remain in this state for a long period of time, or until the host cell is exposed to certain environmental signals. These signals can trigger the prophage into a lytic cycle, in which the viral genes will be expressed and a new virus will be created. This feature of temperate phages makes them useful in medical and biotechnological applications, such as in gene therapy.
In addition to their ability to form prophage, temperate phages also possess unique relationships with endospore-forming bacteria. Spore-forming bacteria carry large numbers of prophage elements in their genomes, and their spores offer more protection for phage DNA than other types of bacteria. This unique relationship between temperate phages and endospore-forming bacteria allows these phages to survive in extreme environments, such as in nutrient-poor, non-living conditions.
In summary, temperate phages are those that have the ability to enter an inactive prophage stage. During this stage, the phage genome is integrated into the host chromosome, forming a prophage. Once the host cell is exposed to certain stimuli, the prophage will be activated and initiate the lytic cycle of viral infection. Temperate phages also possess unique relationships with endospore-forming bacteria, which allow them to survive in extreme environments.