7.3.9: Bacteriophage-Induced Alterations of Bacteria
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- Ying Liu
- City College of San Francisco
Learning Objectives
- 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 Figure \(\PageIndex{1}\) ).
2. Lysogenic conversion by prophages
The added genetic information provided by the DNA of a prophage (Figure \(\PageIndex{4}\)) 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.
The following bacterial exotoxins are a result of lysogenic conversion by a prophage:
- the diphtheria exotoxin of the bacterium Corynebacterium diphtheriae;
- the Streptococcal pyrogenic exotoxin (Spe) produced by rare invasive strains and scarlet fever strains of Streptococcus pyogenes ;
- The neurotoxin produced by Clostridium botulinum ;
- exfoliatin, an exotoxin that causes scalded skin syndrome, produced by Staphylococcus aureus ;
- the cholera exotoxin produced by Vibrio cholerae; and
- 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
- Lytic bacteriophages usually cause the host bacterium to lyse.
- The added genetic information provided by the DNA of a prophage may enable a bacterium to possess new genetic traits.
- 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.
- Examples include the diphtheria exotoxin, streptococcal pyrogenic exotoxin (Spe), the botulism exotoxins, the cholera exotoxin, and the shiga toxin.