cells contain prophage and are known as lysogens. Lysogens can remain in the lysogenic cycle for many generations but can switch to the lytic cycle at any time via a process known as induction. During induction, prophage DNA is excised from the bacterial genome and is transcribed and translated to make coat proteins for the virus and regulate lytic growth. An example of a virus that uses the lysogenic cycle to its advantage is the Herpes Simplex Virus. After first entering the lytic cycle and infecting a human host, it enters the lysogenic cycle. This allows it to travel to the nervous system’s sensory neurons and remain undetected for long periods of time. In the case of genital herpes, latency is established in lumbosacral dorsal root ganglia, spinal nerve neurons. The herpes virus can then exit this dormant stage and re-enter the lytic cycle, causing disease symptoms. Thus, while herpes viruses can enter both the lytic and lysogenic cycles, latency allows the virus to survive and evade detection by the immune system due to low viral gene expression. The model organism for studying lysogeny is the lambda phage. Prophage integration (also known as homologous recombination), maintenance of lysogeny, induction, and control of phage genome excision in induction is described in detail in the lambda phage article. Fitness tradeoffs for bacteria Bacteriophages are parasitic because they infect their hosts, use bacterial machinery to replicate, and ultimately lyse the bacteria. Temperate phages can lead to both advantages and disadvantages for their hosts via the lysogenic cycle. During the lysogenic cycle, the virus genome is incorporated as prophage and a repressor prevents viral replication. Nonetheless, a temperate phage can escape repression to replicate, produce viral particles, and lyse the bacteria. The temperate phage escaping repression would be a disadvantage for the bacteria. On the other hand, the prophage may transfer genes that enhance host virulence and resistance to the immune system. Also, the repressor produced by the prophage that prevents prophage genes from being expressed confers immunity for the host bacteria from lytic infection by related viruses. Another system, arbitrium, has recently been described for bacteriophages infecting several Bacillus species, in which the decision between lysis and lysogeny is transmitted between bacteria by a peptide factor. Lysogenic conversion In some interactions between lysogenic phages and bacteria, the lysogenic conversion may occur, which can also be called phage conversion. It is when a temperate