Bacteriophage

Bacteriophage

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???

Medical Applications of Phage • “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 Reassessment of Medicinal Phage Spurs Companies to Study Therapeutic Uses American Society for Microbiology News 64:620-623, 1998

Medical Applications of Phage • Exponential Biotherapies (Rockville, MD) – Vancomycin resistant Enterococcus facium and Streptococcus pneumoniae

• Phage Therapeutics (Bothell, WA) – Staphylococcus aureus and Staphylococcus epidermidis

• Intralytix, Inc. (Baltimore, MD) – Salmonella in meat and poultry

• Biopharm Ltd. (Tblisi, Georgia) – Infections associated with burns

• University of Idaho – Escherichia coli O157:H7 in cattle Reassessment of Medicinal Phage Spurs Companies to Study Therapeutic Uses. American Society for Microbiology News 64:620-623, 1998. Phages eyed as agents to protect against harmful E. coli. American Society for Microbiology News 65:666-667, 1999.

Bacteriophage • T4 • Lambda ()

Composition and Structure • Composition – Nucleic acid

Head/Capsid

• Genome size • Modified bases

– Protein • Protection • Infection

• Structure (T4) – Size – Head or capsid – Tail

Contractile Sheath

Tail

Tail Fibers Base Plate

Infection of Host Cells • Adsorption – LPS for T4 • Irreversible attachment • Sheath Contraction • Nucleic acid injection

Types of Bacteriophage • Lytic or virulent phage: Phage that can only multiply within bacteria and kill the cell by lysis. (e.g., T4)

• Eclipse – Early genes – Phage DNA synthesis – Late genes

• Intracellular accumulation • Lysis and Release

Number of Infectious Particles

Lytic Phage Multiplication Cycle Total Phage

Eclipse

Extracellular Phage

Intracellular accumulatio n phase

Time after Infection

Lysis

Assay for Lytic Phage Phage

• Plaque assay – Method – Plaque forming unit (pfu) – Measures infectious particles

Bacteria + Phage

Types of Bacteriophage • Lysogenic or temperate phage: Phage that can either multiply via the lytic cycle or enter a quiescent state in the bacterial cell. (e.g., ) – Expression of most phage genes repressed – Prophage – Lysogen

Events Leading to Lysogeny • Circularization of the phage chromosome – Cohesive ends Cohesive Ends Lygase

Linear Double Stranded

Opened Circle

Closed Circle

Events Leading to Lysogeny • Site-specific recombination – Phage coded enzyme

gal

• Repression of the phage genome – Repressor protein – Specific – Immunity to superinfection

bio

gal bio

gal

bio

Termination of Lysogeny • Induction – Adverse conditions

• Role of proteases

bio

gal

– recA protein – Destruction of repressor

• Gene expression • Excision • Lytic growth

bio

gal

gal bio

gal

bio

Lytic vs Lysogenic Cycle? • Role of repressor • Role of cro gene product • Role of proteases

Significance of Lysogeny • Model for animal virus transformation • Lysogenic or phage conversion – Definition: A change in the phenotype of a bacterial cell as a consequence of lysogeny • Modification of Salmonella O antigen • Toxin production by Corynebacterium diphtheriae