what is the Classification of bacteriophages? what are the uses of Classification of bacteriophages? types of Classification of bacteriophages?

Ictv has a bacterial virus sub comittee working on the classification and nomenclature of bacteriophages
The most extensively studied group of bacteriophages are coliphages so called since they infect the non motile strain-b of e coli
They are designated t1 to t7
All these places are composed almost extensively of dna and protein
The tails of t3 and t7 are very short.
The t-phages range from  about 65-2000nm in length and 80 nm in width
The continuous {or} circular molecule of ds dna is tightly packedin protein head.
The other bacteriophages  for e.coli whose morphology and chemical composition are very different from those of the t- phages
The ƛ­2-phage, for example is much smaller than t-phages and has a single stranded linear rna, rather than dna.it has no visible tail
There are also coliphges that possess ss dna morphologically they can be either icosahedral {or} filamentous
An icosahedral phage with circular ss dna is ø×174 bacteriophages.

Lytic cycle:-

Lytic cycles  involves the following steps:-


It is the first step in  infection of  host bacterial cell by a phage is adsorption
The tip of the virus tail become attached to the cell via specific receptor sites on the cell surphage
Lytic cycle,Lytic cycle mechanism
lytic cycle

In some cases the specific receptor of the bacterium is a part of the bacterial lipopolysaccharide

The adsorption of phage t4 ­ to the host cell by means of the interaction of the tip of the phase core and cytoplasmic membrane of the host spheroplast.
Initial adsorption of the phage to the receptor is reversible


The actual penetration of the phage into the cell is mechanical.
 it may be facilitated by the localised digestion of the certain cell structures either by phase enzymes.
In t-even phages, pentration is achieved when-
The tail fibres of the virus attached to the cell and hold the tail firmly  again at the cell wall.
The sheath contracts driving the tail core in to the cell through the cell wall and membrane.
The virus wat,t1 and t5 that do not have a contractile sheath also inject their nucleic acid the cell envelop, possibily at adhesion sites between the inner and outer membrane.


In t4  transcription occurs in several stages leading the formation of immediately early, delayed early and late gene products.
Bacterial m-rna and  bacterial proteins stop being synthesized within a few minutes after entry of the phage dna.
Bacterial dna is quickly degraded to small fragments.
The amount of phage dna increases after a brief delay.
Immediate early phage  genes are transcribed using the existing bacterial rna polymerase.
Delayed early genes code for phrase enzymes which produce unique phase dna constituent such as 5 hydroxymethyl cytosines.
Delayed early genes also code for polymerase and ligase that play specific rules in phage dna replication and recombination and for a second altered rna polymerase that will transcribe late genes.
Late gene products include structural component of new phage particles{heads,tails&fibers} they also include a phage lysozyme which will ligase  the bacterial releasing the violence

Assembly and release:-

Only after the synthesis of both structural proteins and nucleic acid, the phage, component begin to assemble into the mature phages.
About 25 minutes after intial infection some 200 new bacteriophages have been assembled and the bacterial cell brusts, releasing the new phages  to infect the other bacteria and begin the cycle over again.
T4virus has architectural genes which control the synthesis and assembly of new virus

Lysogenic cycle

lysogenic cycle,lysogenic cycle mechanism
lysogenic cycle

In lysogeny,the viral dna of temporary phage. Instead of taking over the functions of the cell genes, is incorporated into the host dna and becomes a prophage in the bacterial chromosome acting as a gene.
The viral dna is removed from the host chromosome and the lytic  cycle occurs this process is called spontaneous induction.
 infection of a bacterium with the temperate phage can be detected by the observation is that the bacterium is resistant to infection

Mechanism of lysogeny:-

 in some of the infection cells, multiplication of the phage occurs and the lytic cycle takes place. In the other infected cells the multiplication of the phage is repressed and lysogination occurs.
The temperate phage posses a gene that codes for a repressor protein which make the cell resistant to lysis initiated either by the prophage {or} by lytic infection by other viruses.
The repressor protein from ƛ-phage has been isolated and purified it is an acidic protein with molecular weight 26,000.
Repressor proteins reacts with two different operators site on the ƛ-phage genome to prevent the expression of the phage lytic functions and the formation of matured phases particle

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