Bacteriophages

1. Dr.T.V.Rao MD's Undergraduate Series Bacteriophages Dr.T.V.Rao MD

2. Viruses that attack bacteria were observed by Twort and d'Herelle in 1915 and 1917. They observed that broth cultures of certain intestinal bacteria could be dissolved by addition of a bacteria-free filtrate obtained from sewage Dr.T.V.Rao MD's Undergraduate Series What are Bacteriophages

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4. Dr.T.V.Rao MD's Undergraduate Series Bacteriophages under Electron Microscope

5. Dr.T.V.Rao MD's Undergraduate Series Bacteriophage (Phage) • 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???

6. Dr.T.V.Rao MD's Undergraduate Series Bacteriophages: Definition & 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.

7. Like most viruses, bacteriophages typically carry only the genetic information needed for replication of their nucleic acid and synthesis of their protein coats.. They require precursors, energy generation and ribosomes supplied by their bacterial host cell. Dr.T.V.Rao MD's Undergraduate Series BACTRIOPHAGES

8. Dr.T.V.Rao MD's Undergraduate Series Bacteriophages: Classification • At present, over 5000 bacteriophages have been studied by electron microscopy and can be divided into 13 virus families.

9. Dr.T.V.Rao MD's Undergraduate Series Bacteriophage • Bacteriophages make up a diverse group of viruses, some of which have complex structures, including double-stranded DNA.

10. Dr.T.V.Rao MD's Undergraduate Series Bacteriophage

11. Dr.T.V.Rao MD's Undergraduate Series Bacteriophage • Also known simply as a phage; a virus that attacks and infects bacteria. The infection may or may not lead to the death of the bacterium, depending on the phage and sometimes on conditions. Each bacteriophage is specific to one form of bacteria.

12. Dr.T.V.Rao MD's Undergraduate Series Head/Capsid Contractile Sheath Tail Tail Fibers Base Plate Composition and Structure • Composition • Nucleic acid • Genome size • Modified bases • Protein • Protection • Infection • Structure (T4) • Size • Head or capsid • Tail

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14. Dr.T.V.Rao MD's Undergraduate Series Phage entering a bacterial cell

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16. Dr.T.V.Rao MD's Undergraduate Series Bacteriophage showing Lytic and lysogenic cycle

17. Bacteriophages: Virulence Factors Carried On Phage • Temperate phage can go through one of two life cycles upon entering a host cell. • Lytic: Is when growth results in lysis of the host and release of progeny phage. • Lysogenic: Is when growth results in integration of the phage DNA into the host chromosome or stable replication as a plasmid. Most of the gene products of the lysogenic phage remains dormant until it is induced to enter the lytic cycle. Dr.T.V.Rao MD's Undergraduate Series

18. Bacteriophages: Lysogenic Conversion • Some lysogenic phage carry genes that can enhance the virulence of the bacterial host. • For example, some phage carry genes that encode toxins. • These genes, once integrated into the bacterial chromosome, can cause the once harmless bacteria to release potent toxins that can cause disease. Dr.T.V.Rao MD's Undergraduate Series

19. Dr.T.V.Rao MD's Undergraduate Series Bacteriophages • Used for cloning foreign genes among other applications • Proteins and peptides are fused to the Capsid(surface) of the phage • The combination of the phage and peptide is known as a Fusion Protein

20. Dr.T.V.Rao MD's Undergraduate Series Bacteriophages • Used for cloning foreign genes among other applications • Proteins and peptides are fused to the Capsid(surface) of the phage • The combination of the phage and peptide is known as a Fusion Protein

21. Dr.T.V.Rao MD's Undergraduate Series Bacteriophages • Once these Phages are isolated and recovered they can be used to infect bacteria which will create a particle similar to a monoclonal antibody

22. Dr.T.V.Rao MD's Undergraduate Series Lytic and Lysogenic cycle

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25. Bacteriophages: Lysogenic Conversion Examples of Virulence Factors Carried by Phage Dr.T.V.Rao MD's Undergraduate Series

26. In some interactions between lysogenic phages and bacteria, lysogenic conversion may occur. It is when a temperate phage induces a change in the phenotype of the bacteria infected that is not part of a usual phage cycle. Changes can often involve the external membrane of the cell by making it impervious to other phages or even by increasing the pathogenic capability of the bacteria for a host. Dr.T.V.Rao MD's Undergraduate Series Lysogenic conversion

27. Dr.T.V.Rao MD's Undergraduate Series Assay for Lytic Phage Phage • Plaque assay • Method • Plaque forming unit (pfu) • Measures infectious particles • Plaque assay • Method • Plaque forming unit (pfu) • Measures infectious particles Bacteria + Phage

28. Dr.T.V.Rao MD's Undergraduate Series Lytic vsLysogenicCycle

29. Dr.T.V.Rao MD's Undergraduate Series Transduction

30. Dr.T.V.Rao MD's Undergraduate Series Transduction

31. Dr.T.V.Rao MD's Undergraduate Series Bacterial cell wall Bacterial chromosome Capsid DNA Capsid Sheath Tail fiber Tail 1 Attachment:Phage attaches to host cell. Base plate Pin Cell wall Plasma membrane 2 Penetration:Phage pnetrates host cell and injects its DNA. Sheath contracted Tail core 3 Merozoites released into bloodsteam from liver may infect new red blood cells Figure 13.10.1

32. Dr.T.V.Rao MD's Undergraduate Series Tail DNA 4 Maturation:Viral components are assembled into virions. Capsid 5 Release:Host cell lyses and new virions are released. Tail fibers Figure 13.10.2

33. Examples: * Corynebacterium diphtheria produces the toxin of diphtheria only when it is infected by the phage β. In this case, the gene that codes for the toxin is carried by the phage, not the bacteria. * Vibrio cholerae is a non-toxic strain that can become toxic, producing cholera toxin, when it is infected with the phage CTXφ. * Clostridium botulinum causes botulism. * Streptococcus pyogenes causes scarlet fever. * Shiga toxin * Tetanus Dr.T.V.Rao MD's Undergraduate Series

34. Dr.T.V.Rao MD's Undergraduate Series Medical Applications of Phages “I strongly believe phage could become an effective antibacterial tool” - Carl Merril, Chief of the Laboratory of Biochemical Genetics, National Institute of Mental Health, NIH. • “It might be another string on the bow, such that when (conventional antibiotics) fail, here’s something that has a chance of working. But it’s not going to be a panacea” - Joshua Lederberg, Sackler Foundation Scholar at The Rockefeller University

35. Dr.T.V.Rao MD's Undergraduate Series • The Programme Created by Dr.T.V.Rao MD for Undergraduate Learning in Developing Countries • Email • doctortvrao@gmail.com