Bacteriophage

Bacteriophage  Definition - Obligate intracellular parasites that multiply inside bacteria by making use of some or all of the host biosynthetic machinery. A bacteriophage is any one of a number of viruses that infect bacteria.  Typically bacteriophages consist of an outer protein enclosing genetic material. The genetic material can be ssRNA, dsRNA, ssDNA, or dsDNA with either circular or linear arrangement.

Types of Bacteriophage  Lytic or virulent phage: Phage that can only multiply within bacteria and kill the cell by lysis.  Lysogenic or temperate phage: Phage that can either multiply via the lytic cycle or enter a quiescent state in the bacterial cell.

Lysis or Lysogeny  Lysis: Infection by phage produces many progeny and lyses the host bacterium  Lysogeny: After infection, the phage DNA integrates into the host genome and resides there passively – No progeny – No lysis of the host

Lysogenic Pathway

Integration

Lytic Pathway

Replication of phage DNA and Protein

(prophage)

Assembly Lysi

ase e l e s&R

Lytic vs Lysogenic Cycle?  Role of repressor (c-I gene).  Role of anjtagonizer of cro gene product.

Significance of Lysogeny  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

Infection by temperate phage leads to lysis or lysogeny E. coli cell

E. coli cell

E. coli chromosome

λ phage +

+

cell undergoeslysogeny

lyticgrowthof phage

λ

λ prophage