Chapter 4 bacteriophage

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Chapter 4 bacteriophage
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• Bacteriophages ( phages ) are obligate
  intracellular parasites that multiply inside
  bacteria by making use of some or all of the host
  biosynthetic machinery . They are viruses that
  infect bacteria.

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Composition of Bacteriophage

• Nucleic acid either DNA or RNA but not both
• ds DNA, ss RNA, ss DNA
• unusual or modified bases
• encode 3-5 gene products to over 100 gene
  products
• Protein function in infection and protect the
  nucleic acid

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Structure of Bacteriophage

• different sizes and shapes

icosahedral ????
filamentous
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Head
Tail
Base Plate
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Types of Bacteriophage

• Lytic or Virulent Phages
• ?????
• Lysogenic or Temperate Phage
• ????????????

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Lytic or Virulent Phages

• Definition
• Lytic or virulent phages are phages which
  can only multiply in bacteria and kill the cell
  by lysis at the end of the life cycle.

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• Life Cycle
• Adsorption??
• Penetration??
• Biological Synthesis????
• Maturation and Release?????

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Adsorption??
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Penetration??
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Biological Synthesis????
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Maturation and Release?????
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Bacteriophage binding to and injecting their DNA
into a bacterial cell
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bacteriophage after contraction of sheath
normal bacteriophage
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Assay for Lytic Phage

• Plaque assay????

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• Lytic phage are enumerated by a plaque assay. A
  plaque is a clear area which results from the
  lysis of bacteria. Each plaque arises from a
  single infectious phage. The infectious particle
  that gives rise to a plaque is called a pfu
  (plaque forming unit).

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Lysogenic or Temperate Phage????????????

• Lysogenic or temperate phages are those that can
  either multiply via the lytic cycle or enter a
  quiescent state in the cell. In this quiescent
  state most of the phage genes are not
  transcribed the phage genome exists in a
  repressed state. The phage DNA in this repressed
  state is called a prophage because it is not a
  phage but it has the potential to produce phage.
  In most cases the phage DNA actually integrates
  into the host chromosome and is replicated along
  with the host chromosome and passed on to the
  daughter cells. The cell harboring a prophage is
  termed a lysogenic bacterium.

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Lysogenic bacterium
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Induction
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?????????????????
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lysogenic conversion?????

• When a cell becomes lysogenized, occasionally
  extra genes carried by the phage get expressed in
  the cell. These genes can change the properties
  of the bacterial cell. This process is called
  lysogenic conversion.

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Application of Bacteriophage

• Used in treatment of bacterial infections
• Used for the identification of pathogenic
  bacteria (phage typing ??????)
• Used in molecular biology