Introductory Microbiology

Bacteriophages

 
• A large number of viruses infecting various bacteria are called bacteriophages.
• The bacteriophages can exist in three phases:

  1) as a free particle-virion
  2) in a lysogenic state as a prophage and
  3) in the vegetative state-lytic cycle.
• As a virion it is inert and cannot reproduce. In the lysogenic state, the DNA of its phage is integrated within the bacterial DNA and exists in a non-infectious form (prophage) and replicates in synchrony with the bacterial DNA. In the lytic cycle, the phage particle infects the susceptible host, multiplies and causes the lysis of the bacterial cell with concommitment release of progeny viral particles. Also, when the integrated phage is induced to become vegetative phage, the lytic cycle follows. Phage that cause lysis are called virulent phages as opposed to those which can exist in a lysogenic state which are called as temperate phages. Bacteria which carry temperate phages are called lysogenic bacteria, and such bacteria are immune to super infection by the same phage.