B.) Lysogenic cycle:

These are also known as temperate phage because phages multiply via the lytic cycle or may enter a dormant state inside the cell. After entry of genetic material into the host cell, the phage DNA integrates into the host chromosome and starts replication along with it and passed to the daughter cells of host. Integration of phage DNA to host chromosome is termed as prophage and bacteria is termed as lysogenic bacteria. Due to integration of phage DNA to host chromosome, extra genes carried by phage get expressed in the host cell and it may change the properties of bacterial cell. This process is termed as lysogenisc or phage conversion.

Due to exposure to UV rays, ionizing radiations, mutagenic chemicals etc, DNA of phage is released from host chromosome and separated phage DNA initiates lytic cycle resulting in the lysis of cell and release of phages into the medium.

Significance of bacteriophages:

• •  New characteristics are acquired using lysogenic conversion

•  Insertional mutation can be induced in bacterial chromosome by random insertion of genes or nucleotides.

•  Latent infection in mammalian cells by retroviruses can be studied using Lambda phage as model system.

•  In genetic engineering, phages are used extensively where they serve as cloning vectors.

•  Phages are used to maintain libraries of genes and monoclonal antibodies

•  Natural removal of bacteria from water bodies can be done using bacteriophages

 

REFERENCES:

Text Books:

1. Jeffery C. Pommerville. Alcamo's Fundamentals of Microbiology (Tenth Edition). Jones and Bartlett Student edition.

2. Gerard J. Tortora, Berdell R. Funke, Christine L. Case. Pearson - Microbiology: An Introduction. Benjamin Cummings.

Reference Books:

1. Lansing M. Prescott, John P. Harley and Donald A. Klein. Microbiology. Mc Graw Hill companies.

2. Biology, Raven and Jhonson, 6 th edition (2001)

3. Microbiology, Pelczar. M.J , Chan E.C.S, Kreig N.R, 5th edition (2007)