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Lysogeny

Lysogeny is the coexistence of bacteria and bacteriophages, in which bacteriophage is an integral part of a normally developing bacterial cell. During lysogenesis, the bacteriophage nucleic acid is incorporated into the chromosome of the bacterium and is reproduced along with it. Proteins are formed, giving the host bacteria a number of new properties, for example, changing its virulence, sensitivity to antibiotics or other bacteriophages. Phage particles are not formed. See also Bacteriophage, Genetics (microorganisms).

Lysogeny (from the Greek. Lysis - decay, destruction and gennao - create, produce) - the inherited property of a bacterial cell to form an infectious bacteriophage and release it into the environment. Bacterial cultures with this property are called lysogenic.

The phenomenon of lysogeny was discovered by Lions (A. Lwoff) and Gutmann (A. Gutmann), who showed that individual cells were you. megaterium is repeatedly divided without phage isolation, but after the 19th division, the daughter bacterium lyses, releasing the active phage (see Bacteriophage). It has not yet been possible to detect active phage or phage antigens inside the lysogenic bacteria. It has been established that in the lysogenic bacterium the bacteriophage is in a special form, which differs from the mature phage. This form, which Lvov called a prophage, is phage DNA combined with bacterial DNA. Thus, the state of lysogeny is an example of combining the genetic apparatus of a virus (phage) with the host chromosome (bacteria).

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Profag is non-pathogenic for a bacterial cell and reproduced simultaneously with the bacterial chromosome. Only transformation of the prophage into a mature phage turns out to be lethal for the bacterium. The ability to induce lysogenesis in bacteria is inherent in certain so-called moderate phages. Infection of a bacterial cell by such a phage, culminating in the establishment of a state of lysogeny, is called reductive, in contrast to the productive one, which ends in the multiplication of phage and cell lysis. Lysogenicity acquired by bacteria as a result of infestation by a moderate phage is a very persistent property that lasts for many years. However, reversal of lysogenic cells to non-isogenicity is possible.

Mild phages lysogenizing the bacterium are combined with its chromosome, usually in certain areas. For example, the λ phage is localized in the E. coli K12 chromosome next to the gene controlling the breakdown of galactose, and phage 080 is linked to tryptophan synthesis genes. Lysogenic bacteria acquire immunity to re-infection with homologous phage. It has been proven that this form of cell immunity is due to the inability of the DNA of a superinfective phage to induce syntheses in the cell, leading to the formation of phage proteins and DNA.

The conversion of a prophage into a vegetative and then into a mature phage is called induction. This process can occur spontaneously or under the influence of external factors, of which the most active is ultraviolet irradiation. The induction mechanism has not yet been precisely studied, but it is known that, as a result, its phage chromosome is autonomous, unrelated to the chromosome of the bacterium, and the synthesis of phage particles begins in the cell. Of particular interest is the fact that most inducing agents are mutagens (see Mutation), and many of them are carcinogenic (see Carcinogenic substances). In some cases, the lysogenization of bacteria is accompanied by a change (conversion) of some of its properties. For example, moderate diphtheria phages have been described, the lysogenization of which causes the toxigenicity of the diphtheria bacillus.

See also genetics of bacteria, viruses.