Bacteriophages

Bacteriophages

The bacteriophages are commonly called 'phages'. The phages possess dsDNA, ssDNa, dsRNA or ssRNA as genetic material. Three common forms (viz., tailed, cubic, and filamentous) of bacteriophages are know.

The tailed bacteriophages from the largest group and are much studied; they have been named 'T-phages' particularly 'T-even phages (T₂, T₄ and so on)' and T-odd phages (T₁, T₃ and so on)'.

However, on the basis of their interaction with the host bacterium, the phages are divided into two groups: virulent and temperate. Virulent phages are those that normally lyse (destroy) the attached host/bacterial cells; there is probably no alternative strategy for their multiplication. This characteristic growth of virulent bacteriophages is called 'lytic cycle' (e.g. T-even phages).

Contrary to the virulent phages, temperate phages adopt two alternative modes for their multiplication, (a) they may enter a lytic cycle and behave like a virulent phage, or (b) they may integrate themselves into the bacterial chromosome thus resulting in a 'Iysogenic cycle'; in the integrated (Iysogenic) state the phage is described as a 'prophage' (e.g. Lambda phage).

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