Virology

1. Virology lab 3
The Structure Of Bacterial Viruses Using
Electron Micrograph
T. Amani Alsharidah

2. Bacteriophages
•Bacteriophage, also called phage or bacterial virus, any of a group of viruses that infect
bacteria.
•Bacteriophage means “bacteria eater”.
•Thousands of varieties of phages exist, each of which may infect only one type or a few
types of bacteria.
•Phages are classified in a number of virus families; some examples include Inoviridae,
Microviridae, Rudiviridae, and Tectiviridae.
•phages are simple organisms that consist of a core of genetic material (nucleic acid)
surrounded by a protein capsid. The nucleic acid may be either DNA or RNA and may be
double-stranded or single-stranded.
Two life cycles, lytic (virulent) or lysogenic (temperate).

3. Bacteriophage Structure

4. Types of Phages
There are three basic structural forms of
phage:
1. An icosahedral (20-sided) head with a
tail
2. An icosahedral head without a tail.
3. A filamentous form.

5. 1- Lambda phage (λ)
•A temperate bacteriophage, an obligate parasite.
• It belongs to the family of lambdoid phages, that includes
phages ϕ21, ϕ80, ϕ81, etc.
•Lambdoid phages are characterized by cohesive ends, the ability
to recombine, and inducibility by UV.
•Each λ particle contains in its icosahedral head (0.05 μm in
diameter) one double-stranded DNA molecule of ca. 49,502 bp
•In its E. coli host it can replicate either and produce hundred
progeny particles in 50 min at 37°C.
•Alternatively, it may insert into the host chromosome as a
prophage.

6. Electron micrograph of Lambda Phage λ

7. 2- T4 phage
•Bacteriophage T4 is one of the seven Escherichia coli
phages (T1–T7), T for type.
•Bacteriophage T4 is classified as a member in the
Myoviridae family, because it has a contractile tail.
•It has highly symmetrical heads, tails and baseplates.
•It has dsDNA genome of 168 Bp.
•The contractile tail improves the efficiency of infection by
making it possible for the tail tube to penetrate the outer
host cell membrane prior to the delivery of phage DNA
into the host cell.

8. T4 Phage Structure
•Capsid (head): polyhedral and the tail sheath is
helical.
•The tail has an inner hollow tube called core,
surrounded by a contractile sheath which consist of
24 annular rings.
•The distal end of the tube is connected to a
hexagonal basal plate with spike or tail spin at each
corner.
•Six long, flexible tail fibers also arise from the basal
plate.

9. Electron micrograph of T4

10. 3-Bacteriophage phiX174 (ɸX174)
Bacteriophage phiX174 hijacks bacterial cells and
forces them to make new copies of the virus.
PhiX174 is composed of a single circle of DNA 5386
Bp surrounded by the icosahedral protein.
Sixty copies of the capsid protein form a spherical
shell around the DNA.

11. Electron micrograph of phX174