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Biology LibreTexts

10.9: Bacteriophage-Induced Alterations of Bacteria

Skills to Develop

  1. Describe the process of lysogenic conversion and give two examples of exotoxins that result from lysogenic conversion.

1. Lytic bacteriophages usually cause the host bacterium to lyse (see Fig. 1).

2. Lysogenic conversion by prophages

The added genetic information provided by the DNA of a prophage (Fig. 4) may enable a bacterium to possess new genetic traits. For example, some bacteria become virulent only when infected themselves with a specific temperate bacteriophage. The added genetic information of the prophage allows for coding of protein exotoxin or other virulence factors.

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Fig. 4: Prophage Formation during the Lysogenic Life Cycle of a Temperate Bacteriophage. The bacteriophage inserts its genome into the nucleoid of the bacterium to become a prophage.

The following bacterial exotoxins are a result of lysogenic conversion by a prophage:

  1. the diphtheria exotoxin of the bacterium Corynebacterium diphtheriae;
  2. the Streptococcal pyrogenic exotoxin (Spe) produced by rare invasive strains and scarlet fever strains of Streptococcus pyogenes;
  3. The neurotoxin produced by Clostridium botulinum;
  4. exfoliatin, an exotoxin that causes scalded skin syndrome, produced by Staphylococcus aureus;
  5. the cholera exotoxin produced by Vibrio cholerae; and
  6. the shiga toxins produced by E. coli O157:H7.

Animation of the Lysogenic Life Cycle of a Temperate Bacteriophage

Exercise: Think-Pair-Share Questions

State why bacteriophages themselves are harmless to humans but might enable certain bacteria to be more harmful to humans.

Summary

  1. Lytic bacteriophages usually cause the host bacterium to lyse.
  2. The added genetic information provided by the DNA of a prophage may enable a bacterium to possess new genetic traits.
  3. Some bacteria become virulent only when infected themselves with a specific temperate bacteriophage. The added genetic information of the prophage allows for coding of protein exotoxin or other virulence factors.
  4. Examples include the diphtheria exotoxin, streptococcal pyrogenic exotoxin (Spe), the botulism exotoxins, the cholera exotoxin, and the shiga toxin.

Contributors

  • Dr. Gary Kaiser (COMMUNITY COLLEGE OF BALTIMORE COUNTY, CATONSVILLE CAMPUS)