Download Bacteriophages: what are they?

4/18/11
Bacteriophages:
Genes and Genomes
Part 1. Bacteriophages:
What are they?
Graham F. Hatfull
University of Pittsburgh
Discovers of Bacteriophages
Felix D’Herelle Frederick Twort
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The plaque test
Anatomy of a bacteriophage
Head
(capsid)
DNA
Tail
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Caudovirales: the dsDNA tailed phages
Myoviridae
Siphoviridae
Podoviridae
Caudovirales: Morphology & Nucleic Acids
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Bacteriophage lytic growth
Phage life cycles: Lysogeny and Lytic growth
Lysogeny
Induction
(spontaneous/UV)
(parasitism:
no viral reproduction,
no cell death)
Lytic growth
(viral production/
cell lysis)
Temperate
Turbid plaque
Lytic
Clear plaque
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Temperate phages form turbid plaques
(from which lysogens can be recovered)
Non-lysogen
Lysogen
Integration confers prophage stability
attP
attB
Integration
Int-Y!
IHF
attL
Excision
Int-Y!
IHF!
Xis
attR
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Bacteriophages: The numerical majority
The viral population is vast
106 - 107 viral particles/ml
1031 viral particles in biosphere
Bacteriophages: A dynamic majority
The viral population is dynamic
5:1 - 10:1 phage:bacteria
1024 viral infections per second
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Bacteriophages: Spanning enormous diversity
The viral population is highly diverse
~650 sequenced genomes
Many different sequences
Large numbers of new genes
So….
•  Bacteriophages represent the
majority of all biological entities
•  A dynamic population has been
evolving for a long time
•  Phages provide the largest
unexplored reservoir of new
genetic information
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