Lysogenic Cycle Definition

Lysogenic Cycle demonstrates a method utilized by viruses to replicate its genome using the host cell molecular machinery.

What is Lysogenic Cycle?

A virus can generally undergo 2 types of replication, the lytic cycle or the lysogenic cycle. In the case of the lysogenic cycle, replication is the main aim as the DNA is replicated but gene products are not expressed.

Whereas in the lytic cycle, the DNA replicates several times and proteins are translated utilizing the host’s machinery. The lysogenic can be usually observed in bacteria or prokaryotes and is also seen in eukaryotes.

A bacteriophage injects its genetic material into its host that is bacteria. The DNA may incorporate into the genetic material of the bacteria and whenever the bacterial cell would divide then the viral DNA would also be replicated using the same molecular machinery of the cell.

It does not alter the molecular processes rather it utilizes them. The quantity of viral DNA produced is less and the machinery is not hijacked as in the lytic cycle. Even though the viral DNA lays latent for some, it can employ the host cell to replicate its DNA through the lysogenic cycle without requiring any effort.

In favorable conditions, the viral DNA may be induced and then it moves to the lytic cycle. Then the viral DNA is transcribed and translated to produce protein coats that are needed to carry the genetic material of the virus.

When the bacteria becomes full of these virions, then they may lyse releasing these intracellular viruses that are ready to infect another host. The lysogenic cycle may continue if conditions are not suitable for the lytic cycle.

This dormant bacterial cell replicates the viral DNA and continues doing so till the lytic cycle is activated. This bacteria that is undergoing a lysogenic cycle may look healthy to an observer.

Lysogenic Cycle Steps

Step 1: The bacteriophage virus injects its DNA into the bacteria that would serve as its host into the cytoplasm, or intermembrane space between the cell wall. This viral DNA integrates into the host genome and is now known as prophage.

Step 2: The viral DNA replicates when the bacterial cell divides and does not have any additional proteins.

Step 3: The viral DNA may continue in the lysogenic cycle, or if conditions are favorable it may switch to the lytic cycle. In the lysogenic cycle, many copies of viral DNA occur in the bacterial cell as the viral DNA is replicated along with the bacterial DNA.

Step 4: When the viral DNA switches to lytic cycle, they employ the host’s machinery to produce the viral proteins required in their assembly and then the virus are packaged.

Step 5: These newly formed temperate viruses are released by the lysis of the cell and they are ready to infect other hosts. After infecting they can start the lysogenic cycle again. If the host condition is not great then they opt for the lytic cycle.

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Lysogenic Cycle Citations

Differential expression of cro, the lysogenic cycle repressor determinant of bacteriophage A2, in Lactobacillus casei and Escherichia coli. Virus Res . 2014 Apr;183:63-6.
The lysogenic cycle of the filamentous phage Cflt from Xanthomonas campestris pv. citri. Virology . 1987 Feb;156(2):305-12.
Lysogenic versus lytic cycle of phage multiplication. Cold Spring Harb Symp Quant Biol . 1953;18:65-70.
Modulation of Lactobacillus casei bacteriophage A2 lytic/lysogenic cycles by binding of Gp25 to the early lytic mRNA. Mol Microbiol . 2016 Jan;99(2):328-37.