MICROBIOLOGY Study Guide - 2012

CHAPTER 6. VIRUSES

6.3. BACTERIOPHAGES

In the Cytology/cytology/16.html">Early stages of bacteriology, many researchers observed and described the effects of Bacteriophages on bacterial cultures.

The lysis of Bacillus anthracis Cells was first observed in 1898 by the Russian scientist N. F. Gamaleya. In 1915, the English microbiologist Frederick Twort described The phenomenon of transmissible lysis in Staphylococcus aureus and suggested that this agent was viral in nature.

In 1917, the Canadian scientist Félix d'Hérelle, independently of F. Twort, reported the ISOLATION OF A specific lytic factor (a virus) from the feces of dysentery patients, which was capable of passing through bacterial filters, multiplying on dysentery Bacteria, and inducing their lysis. D'Hérelle proposed naming this agent bacteriophage (from the Greek fagein, meaning to devour).

Shortly after the discovery of bacteriophages and the recognition of their high lytic activity, researchers attempted to use them for the Treatment and Prevention of infectious diseases. However, the therapeutic efficacy of bacteriophages was inconsistent, and with the discovery of Antibiotics, interest in them as therapeutic agents waned significantly. Later, phages served as highly convenient model systems for investigating various problems in molecular biology, ultimately becoming core objects of genetic research.

The particles of many bacteriophages consist of a round, hexagonal, or rod-shaped HEAD with a diameter of 45–140 nm and a tail measuring 10–40 nm in thickness and 100–200 nm in length. Other bacteriophages lack a tail entirely.

Depending on the Morphology of mature phage particles, the following types are distinguished:

✵ filamentous phages containing single-stranded DNA (coliphage fd);

✵ phages with a short tail (Salmonella phage P22) or a long non-contractile tail (coliphages T1 and T5);

✵ phages featuring a hexagonal head and a tail with a contractile sheath (coliphages T2, T4, and T6);

✵ phages shaped as octahedrons, icosohedrons, etc.

The most extensively studied are the T-even coliphages (T2, T4, T6). They possess an icosahedral head enclosing tightly packed DNA. The tail is a hollow tube surrounded by a contractile sheath. At the distal end of the tail, many bacteriophages feature a baseplate with several spike-like projections. Long, thin fibers extending from the baseplate facilitate the attachment of the phage particle to the bacterial surface. The capsids of both the head and the tail are composed of Proteins. In addition to structural proteins, enzymatic proteins—namely Lysozyme and ATP-ase—have been identified in the phage tail (Fig. 21).

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Fig. 21. Diagram of The Structure of a T2 Escherichia coli bacteriophage particle