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