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Definitions

y From bacteria & Greek phagein to eat

yviruses that infect bacteria

yObligate intracellular parasites that multiply inside bacteriaby making use of some or all of the host biosyntheticmachinery

yShortened form is PHAGE

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STRUCTURETHE STRUCTURE OF A TYPICAL

BACTERIOPHAGE HAS THREE

DISTINCT REGIONS:

yHEAD

yNECK

yTAIL

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Head: Polyhedral in shape

covered by a protein coat called capsid.The capsid is made up of protein unitscalled capsomeres. The capsid enclosesthe nucleic acid. (DNA or RNA)

Neck : Very short and has a collar. Theneck is the portion, which connects thehead and tail.

Tail : has a central, hollow core. A

contractile sheath surrounds it.The tail end of the bacteriophage isattached to a hexagonal shaped endplate Basell plateThe end plate has longfibers with spikes

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Features

y HIGH HOSTSPECIFICITY

y PASSTHROUGH FILTERWHICH HOLD BACKTHE

BACTERIA

y LYTIC PHAGELYSIS THEBACTERIA BEST

DURING ACTIVEPHASEOF BACTERIAL GROWTH

y BOILING INACTIVATETHEPHAGE

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Bacteriophage phi 29

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Bacteriophage Lambda

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ReplicationBacteriophage Replicates By two type of

lifecycle.1. Lytic Cycle

2.Lysogenic Cycle

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y On the Basis of Life Cycle Bacteriophages are of twotypes

y 1. VIRULENT PHAGE:y Replicates through lytic cycle

y Always cause lysis of cell

y Example: T4 Phage

y 2. TEMPERATE PHAGE:y Replicates through Lysogenic Cycle

y Less harmfull

y Example: Lambda Phage

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VIRULENT PHAGE

Lytic cycle

STEPS1. Attachment

2. Penetration

3. ProteinSynthesis

4. Genome Replication

5. Assembly

6. Cell Lysis

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TEMPERATE PHAGE

Lysogenic CycleSTEPS

1. Attachment

2. Penetration

3. Prophage Formation

4. Binary Fission

5. Protein Synthesis

6. Genome Replication

7. Assembly

8. Release

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IMPORTANCE

yMedical Importance

y Industrial Importance

yEcological

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Phage therapy.Phage therapy is the therapeutic use of

bacteriophages to treat pathogenic bacterialinfection.Bacteriophages has advantage over antibiotics.

Traditional antibiotics have more wide-rangingeffect, killing both harmful bacteria and usefulbacteria.The specificity of bacteriophages might reduce the

chance that useful bacteria are killed when fightingan infection.

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Removal OfInfectious Biofilm

y Bacteria forms biofilm on host.

yAntibiotics cannot penetrate into the biofilm.

y

Phage help in destruction of biofilm through cell lysis.

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Rolein Fermentation

y In current industrial fermentation processes phagescan be advantageously employed for the identification

of bacterial production strainsy The propagation of phages in fermentation processes

can cause lysis of the production strains

y Disturbances in the production process and

considerable economic losses.

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Roleinenvironmenty Bacteriophages, like bacteria, are very common in all

natural environments and are directly related to the

numbers of bacteria presenty They have shaped the evolution of bacteria.

y Phages are much more abundant in water.

y They also play role in food web. The lysis of Bacteria by

phages release organic compounds , which makecarbon more available to other organisms.

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