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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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The plaque test

Anatomy of a bacteriophage

DNA

Head (capsid)

Tail

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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