Plasmid

(redirected from conjugative plasmid)
Also found in: Dictionary, Thesaurus, Medical, Wikipedia.
Related to conjugative plasmid: conjugation, R plasmid

Plasmid

A circular extrachromosomal genetic element that is ubiquitous in prokaryotes and has also been identified in a number of eukaryotes. In general, bacterial plasmids can be classified into two groups on the basis of the number of genes and functions they carry. The larger plasmids are deoxyribonucleic acid (DNA) molecules of around 100 kilobase (kb) pairs, which is sufficient to code for approximately 100 genes. There is usually a small number of copies of these plasmids per host chromosome, so that their replication must be precisely coordinated with the cell division cycle. The plasmids in the second group are smaller in size, about 6–10 kb. These plasmids may harbor 6–10 genes and are usually present in multiple copies (10–20 per chromosome). See Gene

Plasmids have been identified in a large number of bacterial genera. Some bacterial species harbor plasmids with no known functions (cryptic plasmids) which have been identified as small circular molecules present in the bacterial DNA. The host range of a particular plasmid is usually limited to closely related genera. Some plasmids, however, are much more promiscuous and have a much broader host range.

The functions specified by different bacterial plasmids are usually quite specialized in nature. Moreover, they are not essential for cell growth since the host bacteria are viable without a plasmid when the cells are cultured under conditions that do not select for plasmid-specified gene products. Plasmids thus introduce specialized functions to host cells which provide versatility and adaptability for growth and survival. Plasmids which confer antibiotic resistance (R plasmids) have been extensively characterized because of their medical importance. Plasmids have played a seminal role in the spectacular advances in the area of genetic engineering. Individual genes can be inserted into specific sites on plasmids in cell cultures and the recombinant plasmid thus formed introduced into a living cell by the process of bacterial transformation. See Genetic engineering

Plasmid

 

a generic term for any intracellular hereditary factor that is not located within the chromosomes. Plasmids include genetic factors in cell organelles, for example, mitochondria and plastids, as well as genetic factors that are not found in any essential components of cells. Of the plasmids that are not associated with any permanent structure, the most extensively studied are the kappa-particle in paramecia (which produces the antibiotic paramecin), the sensitivity factor for CO2, and the agent that inhibits the occurrence of male Drosophila. In addition, several bacteria possess plasmids. Bacterial plasmids control resistance to medicines and regulate the synthesis of bacteriocin, enterotoxin, hemolysin, and certain antigens. The plasmids that are called sex factors control sexual differentiation in bacteria. It has been shown that many plasmids consist of ring molecules of double-stranded deoxyribonucleic acid with a molecular weight that ranges from 106 to 108 daltons.

V. G. LIKHODED

plasmid

[′plaz·məd]
(genetics)
An extrachromosomal genetic element found among various strains of Escherichia coli and other bacteria.
References in periodicals archive ?
CTX-M-14-producing strains show a high level of clonal diversity (11,12); therefore, dissemination has been attributed to conjugative plasmids rather than to clonal expansion of a bacterial host strain (13).
We showed that the emerging clone is multidrug resistant and is characterized by a large conjugative plasmid harboring the Tn1721 transposone and tetA gene, which provides reduced susceptibility to tetracyclines.
Spread and maintenance of conjugative plasmids across bacterial populations have been intensively studied from a theoretical point of view, but data from natural populations are scarce (34,37,38).
The presence of a conjugative plasmid and integrons in this serovar is of clinical importance.
Antibiotic resistance conferred by a conjugative plasmid and a class I integron in Vibrio cholerae O1 E1 Tor strains isolated in Albania and Italy.
Vibrio cholerae O139 multiple-drug resistance mediated by Yersinia pestis pIP1202-like conjugative plasmids.