Micro - 5 - Bacteriphages

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Bacteriphage

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A virus that can infect bacterium in the same way that they can infect humans

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Classification of Bacteriophage

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Lytic
or
Temperate

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What is the difference between viruses that infect humans versus viruses that infect bacteria

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Bacterial viruses inject only their nucleic acid

Human viruses completely enter our cells with their capsid and nucleic acids

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What two macromolecules are bacteriphages made of

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Protein
&
Nucleic acids (DNA or RNA)

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Lytic bacteriphage

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Can be either DNA or RNA

Can immediately replicate to large numbers after infecting cell

Causes bacterium to lyse and die

Life cycle of virus is called lytic pathway

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T2 bacteriophage

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Typical lytic bacteriophage

Infects E-coli therefore also called Coliphage

Consists of:
Capsid head
Tail fibers
Sheath
Neck, collar, base plate
5-hydroxymethylcytosin nucleic acid

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5-hydromethylcytosine

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Nucleic acid that is unique to T2 phage

Positive test can be an indicator that E-coli is infected

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T2 Capsid

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Head of phage

Consists icosahedron of 20 triangle shaped capsomere proteins

Function is to protein the DNA

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T2 Tail fibers

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Helps adsorption

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Adsorption

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Process where structures on the phage help bind to surface receptors on the bacterial cell wall

Assisted by:
Tail fibers
Cofactors
Adhesion receptors

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Penetration

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The sheath plunges downward to inject the DNA or RNA into the bacterium

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Replication

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Virus takes over the bacterium's metabolic machinery to make viral mRNA

early proteins created are to help synthesize new viral nucleic acids

later proteins help synthesize new structural components and lysozyme to weak the bacterial cell

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Self-assembly

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Putting the structural components together and stuffing the nucleic acid into the capsid head

requires no energy

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Maturation

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Hundreds of viral progeny have been made within 30 mins

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Lysis

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Weakened bacterium bursts open releasing the viral progeny

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Temperate phages

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These viruses are always DNA

Quietly integrate into the bacterium's genome and divides its own DNA with the bacterium as it replicates

Life cycle is called lysogenic pathway because they have the potential to break away from the chromosome at some point and replicate and lyse

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Lamba Phage

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Typical temperate bacteriophage

Infects E-coli

Circularizes its DNA before always integrating near the GAL-locus of the bacterium genome

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Prophage

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Viral DNa that got integrated into host DNA

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Adsorption - Lysogenic cycle

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Tail fibers bind to surface receptors on the bacteria's cell wall

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Penetration - Lysogeninc cycle

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Sheath plunges downward to inject the DNA into the bacterium

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Integration - Lysogenic cycle

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DNA Splices itself into the bacterium's genome

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Replication - Lysogenic cycle

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DNA quietly sits in host chromosome and gets replicated every time bacterium replicates

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Lysogenic conversion

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New properties that the bacterium acquires as a result of expression of integrated prophage genes

Can cause non-pathogenic bacterium to become pathogenic due to toxin production

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Lysis - Lysogenic cycle

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Certain things (UV light) will trigger the prophage to disassociate from the bacterium's genome and then enter the lytic cycle