Bacteriophage

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What are Bacteriophage

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Bacteriophages are viruses that can infect and destroy bacteria. They have been referred to as bacterial parasites

Obligate intracellular parasites that multiply inside bacteria by making use of some or all of the host biosynthetic machinery

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Bacteriophage also known

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phage

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Phage Structure

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Capsids or Icosahedral Heads Elaborate Tails (Necessary for Cell membrane/wall penetration)

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Phage Genome

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Subcellular structure without metabolic

DNA or RNA Depending on Type Length of Nucleic Acid Indicates Complexity

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Composition and Structure

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Composition − Nucleic acid Head/Capsid Modified bases Contractile Tail Sheath

Tail Fibers

Head or Infection Base Plate capsid

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Where are Bacteriophage Found?

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Everywhere!Waste-Water Treatment Facilities

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Classification of bacteriophages

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Morphology - Head shape, contractile, noncontractile tails, tailless, filamentous nucleic acid properties dsDNA, ssDNA, ssRNA, dsRNA

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Important term

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Prophage viral genome of temperate phage

Temperate phage capable of lysogeny

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What receptor sites are there for phages on bacteria?

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T-even: proteins, lipopolysaccharides

Teichoic acids, cell wall components Carbohydrates, Sex pilus

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Types of Bacteriophage based on their life cycle

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Virulent phage and template phage

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Types of life cycle

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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

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steps in Phage life cycle

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1)Landing

2)Pinning

3)Tail Contraction

4)DNA Injection

Absorb to Surface Receptor of Bacterial Cell, Penetration of Genome Through Tail Tube into Host Cell . Phage Circularizes DNA (Protects From Nucleases) . Phage Parts Are Produced and AssembledLysozyme. Packaged into Tail Base Plate .Phage Released From Cell

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Mechanism of Lytic or Lysogenic decision?

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cl and cro compete for same binding site on phage DNA

cl = represses synthesis of all genes - lysogenic

cro = represses synthesis of cl lytic

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Lysogenic conversion

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change induced in host phenotype by presence of prophage due to expression of additional genes from prophage

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Examples of lytic and lysogenic dsDNA

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lytic = T4

lysogenic = lambda

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pathogenisis

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Holin enzyme that pokes holes

lysin enzyme that breaks host cell wall peptidoglycan

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Assay to determine presence of phage

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Phage Assay

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Applications of bacteriophages

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Modelsystem of molecular biology

Cloningand expression

Phagedisplay system Phagetyping Phagetherapy: phage as natural,self-replicating, self-limiting antibiotics

Alternative treatment for bacterial infections because self-replicating, smart drugs and narrow specificity

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Image

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