This document discusses bacteriophages, which are viruses that infect bacteria. It covers the definition, history, classification, morphology, life cycle, and applications of bacteriophages. Bacteriophages were discovered in the early 20th century and can have either a lytic or lysogenic life cycle. They are classified based on their morphology and nucleic acid content. Bacteriophages have potential applications in treating bacterial infections and biotechnology.

1. Bacteriophages
Atiqa Akbar 15211506-056
University of Gujrat

2. CONTENTS
• Definition
• History
• Classification
• Morphology
• Life Cycle
• Lytic Cycle
• Lysogenic Cycle
• Applications

3. DEFINITION
• Bacteriophage, also called Phage or Bacterial
Virus
• Group of viruses that infect bacteria
• More than 10³¹ bacteriophages

4. HISTORY
• Frederick W. Twort in Great Britain (1915) –
Staph col – degen.
• Félix d’Hérelle in France (1917) – dysentry
• D’Hérelle coined the term bacteriophage,
meaning “bacteria eater”
• (Phagein) - "to devour"

5. CLASSIFICATION
• International Committee on Taxonomy of
Viruses (ICTV) according to morphology and
nucleic acid.
• 19 families, in which:
2 families have RNA genomes
5 families – envelope
8 families with DNA genomes - circular genomes
9 (DNA) - linear genomes

6. MORPHOLOGY
• Tadpole, which consist on:
Hexagonal Head
Cylindrical tail

7. Cont.
• Head
HTightly packed core of ds DNA
Surrounded by Protein coat / Capsid
• Tail
Hollow core
Contractile sheath surr
Terminal base plate
Attached prongs / fibres
• Spherical / filamentous
• ss DNA / RNA

8. LIFE CYCLE
LYTIC PHASE
• Virulent
• Intracellular
multiplication
• Bacterial host – lysis
• Release of progeny
virions
LYSOGENIC PHASE
• Temperate
• Phage DNA combines
with host s DNA
• Replicating together
• No harm to host

9. LYTIC CYCLE
• Adsorption
• Penetration
• Synthesis of phage components
• Assembly
• Maturation
• Release

10. ADSORPTION
• Attaches to bacterial surface to area having
complimentary receptors to its base plate
• Rapid – minutes
• Location of bacterial Rs – cell wall / Flagella / Pili
• Protoplasts – Not infected ( Transfection )

11. PENETRATION
• Lysozyme on tail makes hole
on surface
• Hollow core pierces the cell
wall
• Contractile tail sheath
propels nucleic acid in
bacteria
• Initiates synthesis of
daughters
• Empty head and tail remain
outside

12. SYNTHESIS OF PHAGE COMPONENTS
• First synthesised – Early proteins
• Enzymes – manufacture of complex molecules
– phage specific
• Late proteins – Head and Tail

13. MATURATION
• DNA of daughter phage – Packed into head
• Tail is added
• The previous process and conversion to
infective stage

14. RELEASE
• Lysis of bacterial cell
• Phage enzymes
• Bacteria becomes spherical during replication
of Phage
• Defective cell wall

15. LYTIC CYCLE

16. LYSOGENIC CYCLE
• Symbiotic Relationship
• Enters the bacterial cell
• Integrated in bacterial chromosome
• Prophage
• Replicates synchronously with host DNA
• Lysogeny
• Bacterial host metabolism UNAFFECTED

18. APPLICATION OF BACTERIOPHAGES

19. REFERENCES
Little, J. W. (2005). Phages: Their Role in Bacterial
Pathogenesis and Biotechnology.
Internet Sources
• https://www.khanacademy.org/science/biology/biolog
y-ofviruses/virusbiology/a/bacteriophages
• https://www.britannica.com/science/bacteriophage

20. Thankyou