Classification of Bacteriophages

Classification of Bacteriophages
On the basis of presence of single or double strands of genetic material, the bacteriophages are categorized as under:

1. The ssDNA Bacteriophages
(i) Icosahedral phages = φ ´ 174, St-1, φR, BR2, 6SR
U3 and G series e.g., G4, G6, G13, G16. All are like φ ´ 174.

(ii) Helical (filamentous)
(a) The Ft group: They are F specific phages and absorb to the tip of F type sex pilus, e.g., E.coli phages (fd, fl, N13).
(b) If group: They are absorbed to I-type sex pilus specified by R factors e.g., If1, If2, etc.
(c) The third group is specific to strains carrying RF1 sex factor.


2. The dsDNA Phages
Following are the examples of dsDNA phages:
(i) T-odd phage of E.coli e.g. T1, T3, T5, T7
(ii) T-even phage of E.coli e.g.T2, T4, T6
(iii) The other E.coli phages e.g., P1, P2, Mu, φ80.
(iv) The phages of Bacillus subtilis e.g., PBSI, PBSX, PBSI, SPOI, SPO2.
(v) The phage of Shigella a e.g., P2
(vi) The phage of Salmonella e.g., PI, P22.
(vii) The phage of Haemophilus e.g., HPl.
(viii) The phage of Pseudomonas e.g., PM2.


3. The ssRNA phages
Examples of the ssRNA bacteriophages are as below:
(i) Group I : E. coli. phages such as f2, MS2, M12, R17, fr, etc.
(ii) Group II : The QP phages.

4. The dsRNA phages
Example: The φ6 bacteriophage.