PHAGE CONVERSION

From Big Medical Encyclopedia

PHAGE CONVERSION — one of types of variability of bacteria caused by the genome of a bacteriophage which was implemented into the polinukleo-tidny sequence of DNA of a bacterial cell. Acquisition by a cell of a new phenotypical sign as a result of F. to. it is not connected with disturbance of the genetic information which is available in it (see Bacteria, the geneticist), and is a consequence of addition to a genome of bacteria of genes of a bacteriophage (see). Originally this form of variability was described at lysogenic bacteriums (see Jiizogeniya) therefore she received the name of lysogenic conversion. It was established later that conversion can be caused and virulent (i.e. killing a bacterial cell) mutants of the converting phages therefore this phenomenon was renamed into phage conversion. Gena (see the Gene), responsible for F. to., are located as a part of a genome of a bacteriophage similar to the genes providing specific transduction (see).

Phenotypical manifestations F. to. are very different. It caused ability to synthesis of toxins at Clostridium botulinum, Clostridium tetani, Corynebacterium diphthe-riae and Corynebacterium ulcerans, change of fagotip and products of hemolysins at Staphylococcus aureus, synthesis of new components of antigens at various Salmonella groups.

The most striking example F. to. conversion of not toxicogenic strains

of S. of diphtheriae in toxicogenic is having medical value. T. to. occurs or owing to lysogenization of bacteria moderate diphtheritic phages, or as a result of lytic (i.e. leading to a lysis) a cycle during a phage infection. It is established that ability to cause conversion is determined by the gene of tox which is a part of a phage genome. During the loss by bacteria of a prophase their ability to produce toxin disappears. Feature F. to. The page of diphtheriae is the fact that formation of toxin goes most actively with a growth of bacteria in the environment with the limited maintenance of ions of iron.

Other example F. to. emergence at bacteria of medicinal stability is (see. Medicinal stability of microorganisms). It is established that ability of bacteriophages to report to bacteria resistance to action of antibiotics (see) and other pharmaceuticals is caused by presence at genomes of bacteriophages of the genetic elements capable to a transposition (i.e. to change of the localization in a genome of bacteria) and called by transposons (see). They can report to bacteria not only any medicines resistance, but also not inherent to them earlier ability to utilize nek-ry carbohydrates or to synthesize enterotoxins.

Distinctiveness F. to. ability of the last to move from a phage genome to genetic structures of a bacterium is caused by transposons. In this case change of a phenotype of bacteria can remain even after their «izlechivaniye» from a genome of a bacteriophage.

Medical - biol. value F. to. is defined by importance of the signs resulting F. to. (toxigenicity, medicinal stability, change of antigenic structure, etc.), for prevention inf. diseases.

Bibliography: And z and z e to I R. R N. Change of heredity of bacteria by phage conversion, in book: Microbiology, under the editorship of A.S. Kriviyeky, t. 3, page 191,

M., 1974; With t e to G.'s t and To e l and N -

d and r River. Molecular genetics, the lane with English, M., 1981; Heys U. Genetika of bacteria and bacteriophages, the lane with English, M., 1965. _ G. B. Smirnov.

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