The episome

The episome - genetic elements bacteria, capable to function in the cell, regardless of the bacterial chromosome. The episome are molecules of DNA. They define in bacteria, the number of features, the most important of which is resistant to antibiotics and sulfa drugs.

The episome (from the Greek. epi and soma - the body) genetic elements that differ from conventional nuclear and cytoplasmic structures that their presence in the cell is not necessary for the implementation of the basic vital functions of the latter. The term "episome" is used to indicate additional, extrachromosomal determinants of heredity in bacteria that can exist in two mutually exclusive States: closely related to the chromosome (integrated) and free in the cytoplasm of bacteria (offline). Biological activity have episome in the offline state. They can multiply and, most importantly, be transferred free from bacteria in the process of conjugation. This process is carried out by co-cultivation of bacteria of donors (media opisannyh elements) and recipients (these items) during the contact surface structures conjugating pairs of cells.
To episomal relate. 1. Moderate bacteriophage (its genetic determinants)that is different from the virulent that, penetrating into sensitive cell, it is not immediately causes lysis of the latter, and enters it in a latent state (in the form of propaga), not manifest themselves until then, until a cage in that condition called litgenas, won't work with agents that induce the synthesis of specific components of phage: nucleic acids and protein. The inductors specific synthesis include ultraviolet rays, some basic dyes and other 2. Colazingari factors determining the synthesis of specific belkooptorg substances (colicins), depressing the development of bacteria related species, and the determinants of synthesis of other bacteriocins (see), known to many bacteria (Magazinov, pesticides, vibriocidal, tuberculocidal and others - more than 20 species). 3. Factors of fertility bacteria, or sex factors, denoted F (fertility). Being integrated in the state (including the chromosome), these factors inform the cell master the ability to transfer chromosomal markers with high frequency. Such cells belong to men strong type and are referred to Hfr. 4. Factors of transfer of resistance to several antibiotics and sulfanilamidam R and RTF. The latter are of epidemiological significance in connection with the possibility of transmission of the determinants of resistance to medicinal substances from representatives of the normal flora to pathogenic agents in conditions of General habitat (for example, in the intestine of humans and animals). Factors episomes drug resistance and factors of fertility harmless to the host cell, whereas temperate phages and colazingari factors in the transition from an integrated offline lead to its demise.
While the above apisannie elements determine various biological phenomena, they have some common properties that determine their genetic behavior. So, all episome consist of molecules of DNA or fixed in a chromosome, or operating autonomously, while in the free state, in the cytoplasm of bacteria. All episome move from integrated into an Autonomous state under the influence of inducing agents; offline they are sensitive to the action of the acrydine dye (acridine orange, acriflavine) and can be eliminated as a result of such action (except colazingari factors, elimination of which acridinae fails). All episome possess the property of transmission - the ability to enter sensitive cell by exogenous (infecting her by type of bacterial viruses) and then transmitted to posterity in an unlimited number of generations. Cell infected by episome becomes immune to homologous factor, while maintaining sensitivity to other episomal. In some cases, however, the presence in the cell of one of AMISOM may limit or completely suppress the activity of another (for example, In and kalitinoy factor). Some colazingari factors can perform the role of factors of fertility in crosses in bacteria. The presence of common traits in Epsom allows to assume their common origin (phylogenetic relationship), but the experimental evidence for this assumption does not yet have.
Biological phenomenon, which is determined by the episome, widely distributed in nature. So, lithogenetic of Salmonella almost constant of their property and can be considered rather as a norm for these bacteria than pathology; colazingari bacteria detected in 30-60% of cases as the representatives of banal intestinal flora and agents of enteric infections. In the latter case, their identification has practical value. Kalininenergo is a persistent feature, allowing to identify the source of infection in epidemiological analysis of outbreaks of diseases caused by pathogens that are not differentiable on serological response. The property is to produce a certain type of kolicina (there are more than 20; types are denoted by capital letters of the Latin alphabet: a, b, D, E and so on) stably preserved not only the typical smooth forms of bacteria, but the rough dissociative forms, giving spontaneous agglutination. Apisannaya resistance to medicinal substances are also widespread, limiting the ability to effectively use the most popular antibiotics (streptomycin, syntomycin, tetracycline) and sulfanilamidov.
The biological value of the prevalence AMISOM in bacteria is very important in connection with the fact that all of them one way or another provide a selective advantage microbial population in conditions of natural habitats. Cm. also, Genetics (bacteria), Variability of microorganisms.