4. BACTERIOPHAGE
• Definition: obligate intracellular parasites that multiply inside bacteria by making use of
some or all of the host biosynthetic machinery.
• Significance
-Models for animal cell viruses
- Gene transfer in bacteria
- Medical applications
- Identification of bacteria - phage typing
- Treatment and prophylaxsis ? ? ?
5. BACTERIOPHAGE
AND HISTORY
⮚Bacteriophages are viruses that can infect and
destroy bacteria.
⮚They have been referred to as bacterial parasites ,
with each phage type depending on a single strain
of bacteria to act as host.
9. MORPHOLOGY :
• Even bacteria can get a virus! The viruses that infect bacteria are
called bacteriophages.
• A bacteriophage, or phage for short, is a virus that infects bacteria. Like other type
of viruses, bacteriophages vary a lot in their shape and genetic material.
• The capsid of a bacteriophage can be icosahedral, filamentous, or head-tail in
shape. The head-tail structure seems to be unique to phages.
10.
11. • It is tadpole-shaped with polyhedral head, a short neck and collar and
a straight tail. The head is bipyramidal hexagonal in shape and
measures 950 x 650 Å. The contents of head are enclosed by a
membrane (capsid) about 35 Å thick.
• The capsid is made up of about 2000 capsomeres .
• The head encloses a linear double stranded DNA, which contains more
than 75 genes. The DNA remains greatly folded.
12. • The tail is in the form of a hollow cylinder. It consists of a central hollow core
surrounded by a spring-like contractile sheath. The sheath is formed of 144
subunits which are arranged in a hollow cylinder consisting of 24 rays of six
subunits each. Through the central space of the core, the phage chromosome
travels into the host cell.
• PARTS :
• Head
• Collar
15. DEFINITION
• Gene transfer from a donor to a recipient by the way of a
bacteriophage.
• Lederberg & Zinder - 1951
16. TYPES OF TRANSDUCTION
i. GENERALIZED : transduction in which potentially any donor bacterial
gene can be transferred.
ii. SPECIALIZED : transduction in which only certain donor genes can be
transferred.
17. GENERALIZED TRANSDUCTION
• Infection of donor.
• Phage replication and degradation of host DNA.
• Assembly of phage particles.
• Release of phage.
• Infection of recipient.
• Homologous recombination.
potentially any donor gene can be transferred.
18. 1. A lytic bacteriophage adsorbs to a
susceptible bacterium.
GENERALISED TRANSDUCTION
2. The bacteriophage genome enters the
bacterium. The genome directs the
bacterium's metabolic machinery to
manufacture bacteriophage components
and enzymes
19. 3. Occasionally, a bacteriophage head or capsid
assembles around a fragment of donor bacterium's
nucleoid instead of a phage genome by mistake.
4. The bacteriophages are released.
20. 5. The bacteriophage carrying the donor
bacterium's DNA adsorbs to a recipient
bacterium
6. The bacteriophage inserts the donor
bacterium's DNA it is carrying into the
recipient bacterium .
21. 7. The donor bacterium's DNA is exchanged
for some of the recipient's DNA.
22. SPECIALIZED TRANSDUCTION
LYSOGENIC PHAGE :
• Excision of the prophage.
• Replication and release of phage.
• Infection of the recipient.
• Lysogenization of the recipient.
-homologous recombination is also possible.
23. SPECIALIZED TRANSDUCTION
• In specialised or restricted transduction, the conducting particle carries
only specific portions of the bacterial genome.
• Specialised transduction is made possible by an error in the lysogenic life
cycle.
24. • When a prophage is induced to leave the host chromosome, excision is
sometimes carried out improperly.
• The resulting phage genome contains portions of the bacterial
chromosome(about 5% to 10% of the bacterial DNA)next to the
integration site.
• A transduction phage genome usually is defective and lacks some part of
its attachment site. The transducing particle will inject another bacterium,
even though the defective phage cannot reproduce.
25. SPECIALISED TRANSDUCTION
1. A temperate bacteriophage adsorbs to a
susceptible bacterium and injects its genome.
2. The bacteriophage inserts its genome
into the bacterium's nucleoid to become a
prophage.
26. 3. Occasionally during spontaneous induction, a
small piece of the donor bacterium's DNA is picked
up as part of the phage's genome in place of some of
the phage DNA which remains in the bacterium's
nucleoid.
4. As the bacteriophage replicates, the segment of
bacterial DNA replicates as part of the phage's
genome. Every phage now carries that segment
of bacterial DNA.
27. 5. The bacteriophage adsorbs to a recipient bacterium
and injects its genome.
6. The bacteriophage genome carrying the donor
bacterial DNA inserts into the recipient bacterium's
nucleoid.
28. SIGNIFICANCE OF TRANSDUCTION
• It transfers genetic material from one bacterial cell to another and alter the genetic
characteristics.
• For example: In specialised transduction the gal gene, a cell lacking ability to
metabolize galactose could acquire the ability .
• It shows the evolutionary relationship between the prophage and host bacterial cell.
• It provides a way to study the gene linkage.
31. • Phages exhibit two different types of lifecycle:
❖ VIRULENT OR LYTIC CYCLE
❖ TEMPERATE OR LYSOGENIC CYCLE
32. • LYTIC CYCLE :
Intra cellular multiplication of the phage ends in the lysis of the host bacterium and
release of progeny virions. Replication of a virulent
Phage takes place in the following stages.
1. ADSORPTION
2. PENETRATION
3. SYNTHESIS OF PHAGE COMPONENTS
4. ASSEMBLY
5. MATURATION
6. RELEASE OF PROGENY PHAGE PARTICLES
33. • 1. ADSORPTION
The attachment of the phage to the surface of a susceptible
Bacterium by means of its tail is called adsorption. Host specificity
of the phage is determined in the adsorption stage of the cycle
Itself. Artificial injection by direct injection of phage DNA can be
achieved even in strains of bacteria that are not susceptible to the
Phage. The infection of bacterium by the naked phage nucleic
Acid is known as transfection.
34. • 2. PENETRATION
The process of penetration resembles injection through a syringe.
The phage DNA is injected into the bacterial cell through the hollow
core. After penetration the empty head and the tail of the naked
phage remain outside the bacterium as the shell.
35. • SYNTHESIS OF PHAGE COMPONENTS
During this stage synthesis of bacterial protein, DNA, and RNA
Ceases. On the other hand, phage DNA, head protein and tail
Protein are synthesized separately in the bacterial cell. The DNA
Is compactly ’packaged’ inside the polyhedron head and finally
The tail structures are added.
36. • The ASSEMBLY of phage components into mature infectious phage
Particle is known as (5) MATURATION.
37. • 6. RELEASE OF PHAGES
Release of phage typically takes place by the LYSIS of the
Bacterial cell. During the replication of phages, the bacterial
Cell wall is weakened and it assumes a spherical shape and
Finally burst or lyse. Mature daughter phages are released.
38.
39. • LYSOGENIC CYCLE
The temperate phages enter into a symbiotic relationship with
the host cells. There is no death or lysis of the host cell. Once inside
the host cell the temperate phage nucleic acid becomes integrated
With the bacterial genome. Now the integrated phage nucleic
Acid is called a prophage.
40.
41. DISEASE CAUSED BY BACTERIOPHAGE
ROLE OF BACTERIOPHAGES IN CHOLERA:
=Cholera is caused by the bacterium VIBRIO
. CHOLERAE
=It is estimated to affect millions of people in
. undeveloped world every year
=Cholera is marked by ACUTE VOMITING and
. DIARRHEA that can dehydrate a person within
. hours
