10.7B: The Lysogenic Life Cycle of Bacteriophages

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    Describe the lysogenic life cycle of temperate phages (including spontaneous induction).
  1. Define the following:
    1. temperate phage
    2. lysogen
    3. prophage

    2. Bacteriophages capable of a lysogenic life cycle are termed temperate bacteriophages. When a temperate bacteriophage infects a bacterium, it can either replicate by means of the lytic life cycle and cause lysis of the host bacterium, or, it can incorporate its DNA into the bacterium's DNA and become a noninfectious prophage (see Figure \(\PageIndex{1}\)). In the latter case, the cycle begins by the bacteriophage adsorbing to the host bacterium or lysogen and injecting its genome as in the lytic life cycle (see Figure \(\PageIndex{2}\) and Figure \(\PageIndex{3}\)). However, the bacteriophage does not shut down the host cell. Instead, the bacteriophage DNA inserts or integrates into the host bacterium's DNA (see Figure \(\PageIndex{4}\)). At this stage the virus is called a prophage. Expression of the bacteriophage genes controlling bacteriophage replication is blocked by a repressor protein, and the phage DNA replicates as a part of the bacterium's DNA so that every daughter bacterium now contains the prophage (see Figure \(\PageIndex{5}\)).

     
     
     
     
     
     

    The number of viruses infecting the bacterium as well as the physiological state of the bacterium appear to determine whether the temperate bacteriophage enters the lytic cycle or becomes a prophage.

    In about one out of every million to one out of every billion bacteria containing a prophage, spontaneous induction occurs. The bacteriophage genes are activated and new bacteriophages are produced by the lytic life cycle (see Figure \(\PageIndex{5}\)A, Figure \(\PageIndex{6}\), Figure \(\PageIndex{7}\), Figure \(\PageIndex{8}\), and Figure \(\PageIndex{9}\)).

     
     
     
     
     
     
     
     
    Name a human viral infection that has a life cycle equivalent to the lysogenic life cycle of bacteriophages.
     
     
     

    This page titled 10.7B: The Lysogenic Life Cycle of Bacteriophages was last modified on Thu, 31 Aug 2023 18:55:22 GMT and is shared under a CC BY 4.0 license and was authored, remixed, and/or curated by Gary Kaiser via source content that was edited to the style and standards of the LibreTexts platform.