Bacteriophages
Bacteriophage Background
• What are bacteriophage?
• Bacteriophage are viruses that infect bacteria.
• It is believed there are approximately 1031
phage particles on the planet with
approximately 1025 infections per second.
•Where are they located?
• Bacteriophage are located anywhere you can isolate bacteria and
are generally abundant in soil and water.
The Discovery of Bacteriophages
(1915-7)
Felix D’Herelle
Source: The Bacteriophages: Ninety years of discovery, Hatfull, 06-23-08
Frederick Twort
Bacteriophage Structure
Bacteriophage come in many different shapes and sizes but all share
several common structural features.
1. Capsid (Head): Comprised of one or more
proteins forming a protective covering around the
nucleic acids. Can vary in shape and size.
2. Genomic Material: Nucleic acids (DNA or RNA,
but not both) contained with the capsid encoding
essential viral proteins. May also encode additional
genes obtained during viral passage.
3. Tail (optional): Hollow protein tube used to
transfer nucleic acids from phage capsid to
bacterium during infection. Can be long or short.
4. Base plate and fibers (optional): Involved in
attachment of phage to bacteria prior to infection.
Source: http://www.bacteriophagetherapy.info/ECF40946-8E2F-48909CA6-D390A26E39C1/Images/Phage-Solo1.jpg
12 Groups of Bacteriophages
Source: http://www.microbiologybytes.com/virology/Phages.html
Three common mycobacteriophage
morphotypes
Myoviridae
• Long, contractile tail
Podoviridae
• Short, contractile tail
Modified from: Suttle (2005) Nature 437, 356
Siphoviridae
• Long, flexible noncontractile tail
Mycobacteriophage genome organization
• Double-stranded
DNA viruses
5’
3’
• Genomes range
in size from 41.4
to 164.6 kb
3’
5’
• Average genome
size is 73.6kb
Source: Hatfull (2010) Ann. Rev Microbiol .64, 331-56.
Mycobacteriophage genome organization
Source: Hatfull (2010) Ann. Rev Microbiol .64, 331-56.
Lytic versus Temperate Phages
Lytic Phage
Temperate Phage
Infection
Lyse All
Infected
Bacteria
Lyse All
Infected
Bacteria
Dormant State
Incorporate
Phage
Genomic DNA
into Host
Genome
Lytic bacteriophages
Source: The Bacteriophages: Ninety years of discovery, Hatfull, 06-23-08
Temperate bacteriophages
Source: The Bacteriophages: Ninety years of discovery, Hatfull, 06-23-08
Important Terms
Lytic Phage: a phage that causes death of the bacterial cell during
viral replication and egress; will likely produce clear plaques
Temperate Phage: a phage that uses one of two strategies for
replication and survival (lysis or lysogeny); will likely produce turbid
plaques
Prophage: the phage genome incorporated into the
bacterial DNA
Lysogen: a bacterial cell with a prophage
Lysogeny: the mechanism by which a naïve bacterial cell becomes
infected with a prophage
Two phage integration systems:
Tyrosine integrases and Serine integrases
Serine Ints
e.g. Bxb1, φRv1, φC31
Tyrosine Integrase
e.g. Lambda
• Catalytic tyrosine
mediates strand
cleavage
• Catalytic serine
mediates strand
cleavage
• Recognize longer
attP sequences
• Recognize shorter
attP sequences
• Require other
phage or hostencoded proteins
Integration
Int-Y
IHF
attL
attP
attP
attB
attB
Excision
Integration
Int-Y
IHF
Xis
Int-S
attR
Modified from: The Bacteriophages: Ninety years of discovery, Hatfull, 06-23-08
attL
• Do not require
other phage or hostencoded proteins
Excision
Int-S
Xis?
attR
Host-specificity
• Phages have been isolated for many (if not most) bacterial hosts
• Phages exhibit host specificity (but can be specific for a sub-species,
species, genus, or beyond!
• The spectrum of ‘infectible’ hosts = host-range
• The inability of a phage to infect a specific bacterial host could be for
multiple reasons:
• Lack of a receptor on the host cell
• Inability of the phage to replicate in that host
• No gene expression
• Presence of a homoimmune prophage
Source: The Bacteriophages: Ninety years of discovery, Hatfull, 06-23-08
Conclusions
• Phages are viruses of bacterial hosts
• Phages are numerous
• Phage populations are dynamic
• Mycobacteriophages are Podoviridae, Myoviridae,
or Siphoviridae.
•Mycobacteriophages have ds DNA genomes
• Phages are typically either lytic or temperate
L5
• Integration into the bacterial host is site-specific
Source: Bob Duda,
University of Pittsburgh
END