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Bacteriophages

Bacteriophages. Viruses that infect bacteria. Named by Felix d’Herelle c.1917 from the Greek phagein , “to devour”. Consist of a nucleic acid molecule surrounded by a protective coat (generally protein). Can only multiply within a bacterial host.

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Bacteriophages

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  1. Bacteriophages • Viruses that infect bacteria • Named by Felix d’Herelle c.1917 • from the Greek phagein, “to devour” • Consist of a nucleic acid molecule • surrounded by a protective coat • (generally protein) • Can only multiply within a bacterial host

  2. Methods for detecting bacterial viruses • Plating environmental samples on susceptible strains • Electron Microscopy • Epifluorescence Microscopy • Amplification of nucleic acid (PCR) from viral communities

  3. Where are bacteriophages found? SourcePhages counted Soil 104/gm Water River 103 - 109/ml Sewage 107 - 108/ml Seawater 107/ml Feces - human 109/gm Shellfish 106/gm Rumen - cattle 109/ml Estimated # of phages in biosphere: 1030

  4. Earth 6 x 1024 kg 1030 cockroaches ~ 5 x 1026 kg

  5. Growth of Phage and Bacteria Bacterial growth: n = n0 2g g = # of generations/hr Phage growth: n = n0 102g if burst size is 100 Infect 106 bacteria with 1 phage; assume equal generation time and burst size =100 Generation # bacteria #phage 1 2 X 106 -2 100 2 4 X 106 - 2 X 102 - 4 104 3 8 X 106 - 2 X 104 - 4 X 102 - 8 106 4 1.6 X 107 - 2 X 106 - 4 X 104 - 8 X 102 - 16 108 at this point, essentially all cells will be infected m.o.I. = 108/1.4 x 107= 7 5 lysis 1.4 X 109

  6. Classification of bacteriophages • Virulent • Always cause destruction (lysis) of the host cell • Temperate • May cause a lytic infection like virulent phage • Have an alternative life cycle in which they • remain dormant inside the bacterial host Phage taxonomy is based on genome properties virion morphology

  7. Siphoviridae: l Myoviridae: T4 Phages with long tails

  8. Phages with short tails - Podoviridae

  9. Tectiviridae: PRD1 Corticoviridae: PM2

  10. Single-stranded DNA phages

  11. RNA Phages Leviviridae: MS2 Cystoviridae: f 6

  12. Requirements for phage survival Protect its genome  Deliver its nucleic acid into a bacterium Convert the infected bacterium to phage production Release progeny phage

  13. Host Range Determinants Phage Receptor T4, P1 LPS core polysaccharide T2 OmpF porin protein T1, T5 TonA ferrichrome transport protein T6 Tsx nucleoside transport protein lambda LamB maltose transport protein chi flagellum (Salmonella) f1, MS2, M13 F-pilus SP-50 Teichoic acid (Bacillus, gram positive) Adsorption Restriction Specific host functions required for phage replication or transcription • E. coli strain EOP, phage grown on: • K-12 B C • K-12 1 10-4 10-4 B 10-4 1 10-4 • C 1 1 1

  14. Lytic life cycle

  15. Adsorption of tailed phages

  16. The Hershey-Chase Experiment

  17. Lytic life cycle

  18. Strategies for Temporal Expression of Phage Genes Repressors Activators Phage-Encoded RNA Polymerase Sigma Substitution Antitermination Translational Repression (especially RNA phages)

  19. Temporal regulation by a phage-encoded activator Early Lysis/lysogeny DNA replication Middle Late gene control Late Capsid, tail, packaging, lysis

  20. Temporal regulation by sigma substitution

  21. Temporal regulation by antitermination Early Delayed early Late

  22. Lytic life cycle

  23. Headful DNA packaging DNA is terminally redundant and circularly permuted DNA is terminally redundant

  24. Site-specific DNA packaging terminally redundant ends

  25. fX174 life cycle

  26. Filamentous phage attachment

  27. Filamentous phage life cycle

  28. ssRNA phages

  29. RNA phage life cycle

  30. Temperate phages and lysogeny

  31. Toxins expressed from prophages (lysogenic conversion) Phage Host Toxin Ctx FVibrio cholerae cholera toxin b Corynebacterium diphtheriae diptheria toxin C-ST Clostridium botulinum botulinum neurotoxin type C1 T12 Streptococcus pyogenes erythrogenic toxin A 933W E. coli O157:H7 Shiga toxin 1

  32. Other virulence factors expressed from prophages Phage Host Product/Function fCTX Pseudomonas aeruginosa Pore-forming cytotoxin f 13 Staphylococcus aureus staphylokinase sopEFSalmonella typhimurium SopE K139 Vibrio cholerae G protein-like virulence factor D3 Psuedomonas aeruginosa O-antigen serotype conversion A3, A4 Salmonella typhimurium O-antigen serotype conversion SfII Shigella flexneri O-antigen serotype conversion

  33. Competing repressors regulate lysis vs. lysogeny

  34. Bacteriophage lambda integration

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