Bacteriophage : Classification and Types of Bacteriophages | Microbiology

In this article we will discuss about the (1) Classification of bacteriophage (2) Types of Bacteriophages.

Essay # (1) Classification of bacteriophage

1. Bacteriophages with DNA Genome:

A. Genome is double-stranded DNA, generally linear.

1. Family Myoviridae:

Icosahedral, isometric or elongated head with a helical rigid tail containing a contractile sheath, tail plate, tail fibres and spikes.
Example: E. coli phage (coliphage) T2, T4, T6.

2. Family Styloviridae:

Icosahedral, isometric head with a long flexible tail without a contractile sheath. Tail fibres may or may not be present.
Example: E. coli phage T1, T5.

3. Family Pedoviridae:

Icosahedral, isometric head with a sheath-less tail which is shorter than the head. Tail fibres may or may not be present.
Example: E. coli phage T3, T7.

4. Family Corticoviridae:

Icosahedral, isometric head without a tail. Capsid contains lipid in addition to protein. The genome is closed circular ds-DNA.
Example: Pseudomonas phage MP2.



5. Family Tectiviridae:

Icosahedral, isometric head without tail. Virion contains double capsid.
Example: phage PRD 1.

6. Family Plasmaviridae:

Virion plemorphic, Enveloped.
Example: Phage MV-L2.

B. Genome single-stranded DNA:

1. Family Microviridae:

Icosahedral, isometric head without tail or envelope.
Example: E. coli phage φX174 having a circular ss-DNA genome.

2. Family Inoviridae:

Helical symmetry; virions long rod shaped or filamentous; non-enveloped; genome circular ss-DNA.
Example: E. coli phage fd and bacteriophage MV-L1.



2. Bacteriophages with RNA Genome:

A. Genome double-stranded RNA

1. Family Cystoviridae:

Capsid icosahedral, enveloped; ds-RNA is segmented; virions more or less spherical, about 90-100 nm in diameter.
Example: Phage φ6.

B. Genome single-stranded RNA

1. Family Leviviridae:

Capsid icosahedral, non-enveloped, ss-RNA is linear (+). Virions 26-27 nm in size.
Example: Phages MS2 and Qβ.

Morphology of some representative bacteriophages is shown diagrammatically in Fig. 6.10:

Essay # (2) Types of Bacteriophages:

The phages have specific host. E. coli has been studied most extensively from this point of view. The bacteriophage capable of destroying E. coli is called coli-phage. The types of coli-phages have been called as T-phages.

They have been classified into many arbitrary groups such as:

(i) T-Even Phages (T2, T4, T6):

These phages have an angular head and contractile tail. The DNA contain a unique base 5-hydroxyl methyl cytosine in place of cytosine. These viruses are most thoroughly studied viruses. These are also called virulent as they cause death of the host cells.

(ii) T-Odd Phages (T1, T3, T7):

These viruses have an angular head and a short non-contractile tail. The DNA contain cytosine. These are temperate viruses as their genetic material becomes integrated with bacterial chromosomes and the host remains unaffected.

(iii) T5 Phages:

These viruses have an angular head and non-contractile tail. The DNA of these viruses also contains cytosine.