1946; Newcobmbe, 1949; Lederberg, Lederberg, 1952). One more avalanche
of investigations occurred in this field. A new branch of biology appeared —
Virology.
The viruses can infect the cells of all kinds of plants, animals and
microorganisms. Their typical feature is that unlike the parasitizing
rickettsiae and bacteria they do not possess their own metabolite system.
That is why, for their developing and reproducing they need the biological
apparatus of recipient cell. Developing in the cells they destroy or lyse them
(Fig. 2–87). As a result the “hosts” perish.
Virulent phages immediately lyse the infected cells. They have only
one way of development, so-called lytic cycle. Also there exist moderate
phages (P1, P2, P22, λ, etc.). They can penetrate into recipient cell without
immediate lysing it and are transferred to its following generations. Such
bacteria are called lysogenic, and the phage — prophage. At a given
moment a prophage can change into virulent and proceed to lysis. The
reasons for that are unclear.
image
Figure 2–87. Electron micrograph of lysed culture of E. coli infected with T2 phage (After Stent, 1974).
Adsorbing the phages is closely connected with the cellular envelope.
Except by living cells. they can also be adsorbed by empty cellular
envelopes. Cells with destroyed envelopes (protoplasts) do not absorb
them, but they develop there if have been included previously. Penetration