general overview on discovery of phage

1. 1
Discovery of
Bacteriophage
copyright cmassengale
Presented by;-
Manahil khanam Durrani.

2. 2
BacterioPhages
‘Bacteriophages are viruses
that infect bacteria’’
The ‘phages’ were
discovered independently
in 1915 and 1917 by
Frederick W. Twort and
Felix d’Herrelle,
respectively
D’Herrelle coined the term
bacteriophage
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3. A brief introduction to the phage world
 Bacteriophages are viruses of bacteria
 Bacteriophages represent the majority of life forms:
Estimated number 1031
The phage population is extremely dynamic: 1025
infections/sec
 Phages are specific to particular bacterial hosts
 Phages are genetically highly diverse, but relatively few
have been characterized
 Phages are the largest reservoir of unexplored genetic
information

4. 4
T-phages
The most commonly studied
T-phages are T4 and T7
They infect E. coli , an intestinal
bacteria
Six small spikes at the base of a
contractile tail are used to
attach to the host cell
Inject viral DNA into cell
copyright cmassengale
T-phages are a specific
class of bacteriophages with
icosahedral heads, double-
stranded DNA, and tails

5. 5
Escherichia Coli
Bacterium
T - EVEN PHAGES ATTACK THIS BACTERIUM
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6. 6
T-Even Bacteriophages
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7. 7
Diagram of T-4
Bacteriophage
Head with 20
triangular
surfaces
Capsid contains
DNA
Head & tail fibers
made of protein
copyright cmassengale

8. 8
First Phage Observations
First reported in 1896 by
Hankin (Pasteur, Paris)
Observed that waters of
the Ganges and Jumna
rivers had potent anti-
bacterial properties
Skin sores and other
infections rapidly
cleared when pilgrims
bathed in the Ganges

9. Frederick Twort
1877-1950
Ultramicroscopic discovery in 1915
•Frederick Twort first discovered
them.
•Observed glassy, clear areas in
colonies of Stapphylococcus
•Could not be cultured
independently
•Could be serially transferred
and propagated on new
bacterial colonies, but not on
dead bacteria
•Passed through a porcelin
filter
•Destroyed by heat

10. Félix d'Herelle
1873-1949
•Bacterial growth media innoculated
with stool from patient with dysentery
•Culture became cloudy overnignt,
indicating growth of bacteria
•Culture was filtered and filtrate
added to pure cultures of Shiga
bacteria (the causative agent of the
dysentery)
•One day, the Shiga culture showed no
growth. At the same time, the patient
had shown marked improvement.
The Bacteriophage: It Role in Immunity (1921)

11. The Bacteriophage: It Role in Immunity (1921)
•Sterile filtrate of cleared
culture could kill other cultures
of Shiga
•Observed plaques on solid media,
developed plaque assay, concept
of titering
•Deduced that active agent was a
virus!
•Showed that bacteriophage
could be used to treat infections

12. The plaque assay
phage
Bacteria + top agar
•Serial dilutions of phage gave rise to decreased numbers of plaques
•a discrete entity (i.e. the virus) is responsible for the plaques
•inferred that 1 plaque arose from a single virus. Thus, plaque
forming units=viruses
•1 plaque is composed of many pfu
•the viruses can replicate!
•Final acceptance of the existence of bacteriophage came with electron
micrographs (Helmut Ruska, 1939)

13. Mycobacteriophages
• Mycobacteriophages are viruses that infect
mycobacterial hosts
• Phages can facilitate understanding of host physiology
• Phages have therapeutic potential
• Some mycobacteria cause important human diseases
• M. tuberculosis kills more people than any other single
infectious agent
• We study phages that infect M. smegmatis, a useful
surrogate bacterium that is not harmful to humans.
• ~10% of phage that infect M. smegmatis also infect M.

14. Kim Davis, in the redwood
forest where she isolated
LRRHood
(Little Red Riding Hood)
Phage LRRHood

15. Mycobacteriophage genomics
• First mycobacteriophage sequence published in 1993
• ~250 completely sequenced genomes
•Genomes range in size from 42-153kbp (kbp= 1000
basepairs)
• Average genome size: ~72kbp
• Average number of genes: 88/genome
• High genetic diversity
• High gene density
• Genomes are genetically mosaic (meaning we can’t
construct a simple “tree of life” for these viruses)
• Most genes of unknown function

16. copyright cmassengale 16