An Introduction to Bacteriophages

1. LECTURE 1: An Introduction to Bacteriophages Viro102: Bacteriophages & Phage Therapy 3 Credit hours NUST Centre of Virology & Immunology

2. Bacteriophages: Definition Viruses that can infect bacteria. Referred to as bacterial parasites. Each phage may infect a single or multiple bacteria depending on the available entry sites.

3. Bacteriophage: An introduction • A bacteriophage are the viruses that infect bacteria. • Typically, bacteriophages consist of an outer protein hull enclosing genetic material. • Size of infectious particle usually between 20 and 200 nm in size. • A phage can persist in other cells but can only replicate within a bacterial cell.

4. Bacteriophage: An introduction • The most abundantly found entities in the biosphere. • They are found in in all habitats in which their hosts i.e. bacteria can survive. (e.g. soil, human intestine, hot springs etc). They have shaped the evolution of bacteria. • One of the densest natural sources for phages and other viruses is sea water, where up to 9×108 virions/ml have been found in microbial mats at the surface, and up to 70% of marine bacteria may be infected by phages. • They have been used for over 60 years as an alternative to antibiotics in the former Soviet Union and Eastern Europe.

5. Bacteriophage: History • In olden times, People observed that river water has the capability of curing infectious diseases such as leprosy. • In 1896, Ernest Hanbury Hankin reported that something in the waters of the Ganges and Jumna rivers in India had marked antibacterial action against cholera and this cannot be filtered. • In 1915, British bacteriologist Frederick Twort, discovered a small agent that infected and killed bacteria. He considered the agent either: • A stage in the life cycle of the bacteria. • An enzyme produced by the bacteria themselves. • A virus that grows on and destroys bacteria.

6. Cont’d • Félix d'Hérelle, announced on September 3, 1917 that he had discovered "an invisible, antagonistic microbe of the dysentery bacillus“ in Pasteur Institute in Paris. • D'Hérelle called the virus a bacteriophage or bacteria-eater. He also recorded a dramatic account of a man suffering from dysentery who was restored to good health by the bacteriophages. • Also in the 1920s the Eliava Institute was opened in Tbilisi, Georgia to research this new science of BACTERIOPAGES and put it into practice. Their main focus was to use bacteriophages against bacterial infections

7. Cont’d • Max Schlesingerin 1936 showed the existence of DNA in phages. • The technique of electron microscopy was developed and the existence and nature of bacteriophages were proven by electron micrographs. • In 1940s with the emergence of antibiotics, bacteriophage studies were almost halted as the use of antibiotics was more economical. • In 2006 the UK Ministry of Defence took responsibility for a G8-funded Global Partnership Priority Eliava Project as a retrospective study to explore the potential of bacteriophages for the 21st century.

8. Head/Capsid Contractile Sheath Tail Tail Fibers Base Plate Bacteriphage: Structure

9. Bacteriophage: Structure • Head or Capsid • All phages contain a head structure which can vary in size and shape. • icosahedral (20 sides)or filamentous. • The head or capsid is composed of many copies of one or more different proteins. • Inside the head is found the nucleic acid. The head acts as the protective covering for the nucleic acid. • Tail • The tail is a hollow tube through which the nucleic acid passes during infection. • The size of the tail can vary and some phages do not even have a tail structure. • Base plate & one or more tail fibers • involved in the binding of the phage to the bacterial cell. • Some phages have other structures in place of base plate to facilitate entry

10. Bacteriophage: Genome • The genetic material can be • ssRNA, • dsRNA, • ssDNA, or • dsDNA • Genome size is between 5 and 500 kilo bases (Kb) • Some phages have fewer than ten genes and depend entirely on cellular functions. • Others may have 30 to 100 genes and depend more on proteins encoded by their own genetic material.

11. Bacteriophage: Survival • Each phage must perform some minimal functions for continual survival. • Protection of its nucleic acid from environmental chemicals that could alter the molecule. • Delivery of its nucleic acid to the bacterium. • Conversion of an infected cell to phage producing system, which yields a large number of phages. • Release of progeny phages from infected cell.

12. Bacteriophage: Infection of host cells • Four basic steps: • Adsorption • Irreversible attachment • Sheath contraction • Nucleic acid injection

13. Bacteriophage: Infection of host cells • Adsorption: • Mediated by the tail fibers or by some analogous structure on those phages that lack tail fibers. • It is reversible. • The tail fibers attach to specific receptors on the bacterial cell and the host specificity of the phage is usually determined by the type of tail fibers.

14. Bacteriophage: Infection of host cells • Irreversible attachment: • Irreversible binding of phage to a bacterium is mediated by one or more of the components of the base plate. • Phages lacking base plates have other ways of becoming tightly bound to the bacterial cell

15. Bacteriophage: Infection of host cells • Sheath contraction: • The irreversible binding results in the contraction of the sheath and the hollow tail fiber is pushed through the bacterial envelope. • Phages that don't have contractile sheaths use other mechanisms to get the phage particle through the bacterial envelope. • Some phages have enzymes that digest various components of the bacterial envelope.

16. Bacteriophage: Infection of host cells • Nucleic acid injection: • When the phage has gotten through the bacterial envelope the nucleic acid from the head passes through the hollow tail and enters the bacterial cell. • Usually, the only phage component that actually enters the cell is the nucleic acid. The remainder of the phage remains on the outside of the bacterium.

17. Just like a syringe injecting vaccine into the blood in animals, a bacteriophage injects its nucleic acid into the bacterial host cell ellsAlive

18. Bacteriophage: Propagation • Once inside the bacterial cell, the Phage nucleic acid can undergo any one of these life cycles • Lytic cycle - lyse the host bacterium as a normal part of their life cycle • Lysogenic cycle - it can incorporate its DNA into the bacterium's DNAand become a noninfectious prophage

19. Bacteriophage: Release Afterwards mature virion particles lyse the cell and they are released into the environment where they can infect other cells

20. Bacteriophages Classification • Over 5000 bacteriophages have been studied and these have been classified into 13 families

21. Bacteriophage: ICTV Classification

23. 13 Bacteriophage families Double stranded DNA, Non-enveloped Double stranded DNA, Enveloped SIRV 1, 2 P2 Rudiviridae Myoviridae Plasmaviridae T2 Fuselloviridae SSV1 TTV1 Tectiviridae λ PRD1 Siphoviridae Lipothrixviridae PM2 P22 Corticoviridae Podoviridae Single stranded RNA Double stranded RNA Single-stranded DNA M13 & fd Inoviridae MS2 phi666 Leviviridae ΦX174 Microviridae Cystoviridae

24. Bacteriophage: Model • A list of bacteriophages that are extensively studied: • λ phage • T2 phage • T4 phage • T7 phage • M13 phage • MS2 phage • P1 phage • Phi X 174 phage • Φ6 phage • Φ29 phage

25. Phages: Applications • Industry • Biotechnology • Medical • Environment • Bacterial evolution

26. Thank you!