Resistance plasmids
(noun)
These plasmids contain genes that provide resistance against antibiotics or poisons.
Examples of Resistance plasmids in the following topics:
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Types of Plasmids and Their Biological Significance
- The gene to be replicated is inserted into copies of a plasmid containing genes that make cells resistant to particular antibiotics.
- Only bacteria that take up copies of the plasmid survive, since the plasmid makes them resistant.
- Just as the bacterium produces proteins to confer its antibiotic resistance, it can also be induced to produce large amounts of proteins from the inserted gene.
- Fertility F-plasmids, which contain tra genes.
- Resistance plasmids, which contain genes that provide resistance against antibiotics or poisons.
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Agrobacterium and Crown Gall Disease
- Argobacterium causes Crown Gall Disease by transferring a DNA plasmid to the host plant, causing the host to make nutrients for it.
- A. tumefaciens can transfer part of its DNA to the host plant, through a plasmid - a bacterial DNA molecule that is independent of a chromosome.
- For example, plasmids can confer on bacteria the ability to fix nitrogen, or to resist antibiotic compounds.
- Typically bacteria transfer plasmids through conjugation: a donor bacteria creates a tube called a pilus that penetrates the cell wall of the recipient bacteria and the plasmid DNA passes through the tube.
- The other bacteria either integrates the plasmid into its chromosomes, or it remains free-floating in the cytoplasm.
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Introduction to Plasmids
- Plasmid sizes vary from 1 to over 1,000 kbp.
- The term plasmid was first introduced by the American molecular biologist Joshua Lederberg in 1952.
- Similar to viruses, plasmids are not considered by some to be a form of life.
- Plasmids may carry genes that provide resistance to naturally occurring antibiotics in a competitive environmental niche, or the proteins produced may act as toxins under similar circumstances.
- The upper half of the image shows a bacterium with its chromosomal DNA and plasmids dividing into two identical bacteria, each with their chromosomal DNA and plasmids.
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Plasmids and Lysogeny
- In addition, plasmid DNA provides a mechanism by which horizontal gene transfer can occur, contributing to antibiotic resistance.
- Horizontal gene transfer is a major mechanism promoting bacterial antibiotic resistance, as the plasmid DNA can transfer genes from one species of bacteria to another.
- The plasmid DNA which is transferred often has developed genes that encode for resistance against antibiotics.
- The ability to transfer this resistance from one species to another is increasingly becoming an issue in clinics for treatment of bacterial infections.
- The advantages of plasmid DNA transfer allow for survival advantages.
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Genetic Analysis
- Bacterial chromosomes contain double stranded molecules of DNA arranged in a circular form called plasmids .
- Plasmids are located in the cytoplasm of bacteria, are capable of autonomous replication, and transfer genes from parent cell to daughter cell.
- Bacteria possess extra chromosomal genetic elements that encode for antibiotic resistance, toxins, virulence determining genes, and reduced sensitivity to mutagens such as heavy metals.
- Plasmid profiling using molecular, biochemical, and microbial techniques is essential to understanding the mechanism of pathogenicity and to fuel genetic engineering.
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Inactivating and Marking Target Genes with Transposons
- Transposons in bacteria usually carry an additional gene for function other than transposition---often for antibiotic resistance.
- In bacteria, transposons can jump from chromosomal DNA to plasmid DNA and back, allowing for the transfer and permanent addition of genes such as those encoding antibiotic resistance (multi-antibiotic resistant bacterial strains can be generated in this way).
- Insertional inactivation is a technique used in recombinant DNA engineering where a plasmid (such as pBR322) is used to disable the expression of a gene.
- An example is the use of pBR322, which has genes that respectively encode polypeptides that confer resistance to ampicillin and tetracyclin antibiotics.
- As a result, when a genetic region is interrupted by integration of pBR322, the gene function is lost but new gene function (resistance to specific antibiotics) is gained.
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Plasmids as Cloning Vectors
- Plasmids may be conjugative/transmissible or non-conjugative.
- Nonconjugative plasmids do not mediate DNA through conjugation.
- Antibiotic resistance: Vectors with antibiotic-resistance allow for survival of cells that have taken up the vector in growth media containing antibiotics through antibiotic selection.
- The pGEX-3x plasmid is a popular cloning vector.
- The various elements of the plasmid are labelled.
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Shuttle Vectors and Expression Vectors
- An expression vector is generally a plasmid that is used to introduce a specific gene into a target cell.
- An expression vector, otherwise known as an expression construct, is generally a plasmid that is used to introduce a specific gene into a target cell .
- Cloning vectors, which are very similar to expression vectors, involve the same process of introducing a new gene into a plasmid, but the plasmid is then added into bacteria for replication purposes.
- The E. coli component of a yeast shuttle vector includes an origin of replication and a selectable marker, such as an antibiotic resistance like beta lactamase.
- The pGEX-3x plasmid is a popular cloning vector.
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Pili and Pilus Assembly
- Perhaps the most well-studied is the F pilus of Escherichia coli, encoded by the F plasmid or fertility factor .
- Typically, the DNA transferred consists of the genes required to make and transfer pili (often encoded on a plasmid), and is a kind of selfish DNA; however, other pieces of DNA often are co-transferred, and this can result in dissemination of genetic traits, such as antibiotic resistance, among a bacterial population.
- Conjugation diagram 1- Donor cell produces pilus. 2- Pilus attaches to recipient cell, brings the two cells together. 3- The mobile plasmid is nicked, and a single strand of DNA is then transferred to the recipient cell. 4- Both cells recircularize their plasmids, synthesize second strands, and reproduce pili; both cells are now viable donors.
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Vectors for Genomic Cloning and Sequencing
- The four major types of vectors are plasmids, viral vectors, cosmids, and artificial chromosomes.
- Plasmid vectors minimalistically consist of an origin of replication that allows for semi-independent replication of the plasmid in the host and also the transgene insert.
- In the case of plasmids utilized as transcription vectors, incubating bacteria with plasmids generates hundreds or thousands of copies of the vector within the bacteria in hours.
- Plasmids may be conjugative / transmissible and non-conjugative.
- Conjugative vectors mediate DNA transfer through conjugation and therefore spread rapidly among the bacterial cells of a population, such as the F plasmid, as well as many R and some col plasmids.