Bacteria

Bacteriophage

-is a virus that infects bacteria. These are obligate intracellular parasites that multiply inside bacteria by making use of some or all of the host biosynthetic machinery.

Bacteriophage

*Bacteriophages that replicatethrough Lytic life cycle are calledLYTIC BACTERIOPHAGES and sonamed because they lyse the hostbacterium as a normal part of their lifecycle.

Types of Bacteriophages*Bacteriophages capable of Lysogenic life cycle are termed TEMPERATE PHAGES. When a temperate infects a bacterium, it can either replicate by means of the lytic cycle or cause lysis of the host bacterium, or it can incorporate its DNA into the bacterium’s DNA and become noninfectious prophage.

Tail

Tail Fibers

Base Plate

Head/Capsid

Contractile Sheath

Parts of Bacteriophages•Head/Capsid

•Tail *Collar *Sheath *Base Plate

Head/Capsid is composed of many copies of one or more different proteins. It is where the nucleic acid found and it act as the protective covering for the nucleic acid.

Tail is a hollow tube through w/c the nucleic acid passes during infection.

* Collar collar attached the whiskers. The fibers are kept folded around the tail , their midpoint being held by whiskers.

* Sheath it is an inner core on the tube w/c contracts during the infection of the bacterium.

* Base Plate/Tail fiber involved in the binding of the phage to the bacterial cell.

LYTIC CYCLE* The life cycle of Lytic bacteriophages in which new viruses are produced within the infected bacterium. The viruses usually lyse the infected host bacterium in order to be released.

Lysogenic Cycle• Where the newly integrated genetic material called prophage can be transmitted into daughter cells at subsequent cell division and a later event can release it, causing proliferation of new phages via Lytic Cycle.

The following are the steps of the Lysogenic cycle:

1. Viral Genome enters cell2. Viral genome integrates into host cell

genome3. Host cell DNA polymerase copies viral

chromosomes4. Cell divides, and virus chromosomes

are transmitted to cell’s daughter cells5. At any moment when the virus is

“triggered”, the viral genome detaches from the host cell’s DNA and enters stage 2 of lytic cycle.

Advantages* Phages are very specific, so they will not harm beneficial bacteria in the body.

* Once the bacteria is destroyed phage action ceases as they no longer have a host and so will disperse harmlessly.

* Phage therapy could be useful for people who are allergic to antibiotics.

Disadvantages* There is huge diversity of

phages, a potential problem if the bacteria to be treated is unknown.

* Some phages are quickly excreted from the bloodstream, having been recognized by immune system.

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