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Encyclopedia > Bacterial conjugation

Bacterial conjugation is the transfer of genetic material between bacteria through direct cell-to-cell contact.[1] Discovered in 1946 by Joshua Lederberg and Edward Tatum,[2] conjugation is a mechanism of horizontal gene transfer—as are transformation and transduction—although these mechanisms do not involve cell-to-cell contact.[3] Joshua Lederberg speaking at a conference in 1997 Joshua Lederberg (born May 23, 1925) is an American molecular biologist who is known for his work in genetics, artificial intelligence, and space exploration. ... Tatum won the Nobel Prize for his work in genetics Edward Lawrie Tatum (December 14, 1909 - November 5, 1975) was an American geneticist. ... Horizontal gene transfer (HGT), also Lateral gene transfer (LGT), is any process in which an organism transfers genetic material to another cell that is not its offspring. ... It has been suggested that this article or section be merged into Transfection. ... Transduction is the process by which bacterial DNA is moved from one bacterium to another by a virus. ...


Bacterial conjugation is often incorrectly regarded as the bacterial equivalent of sexual reproduction or mating. It is not actually sexual, as it does not involve the fusing of gametes and the creation of a zygote, nor is there equal exchange of genetic material. It is merely the transfer of genetic information from a donor cell to a recipient. In order to perform conjugation, one of the bacteria, the donor, must play host to a conjugative or mobilizable genetic element, most often a conjugative or mobilizable plasmid or transposon.[4] Most conjugative plasmids have systems ensuring that the recipient cell does not already contain a similar element. Phyla/Divisions Actinobacteria Aquificae Bacteroidetes/Chlorobi Chlamydiae/Verrucomicrobia Chloroflexi Chrysiogenetes Cyanobacteria Deferribacteres Deinococcus-Thermus Dictyoglomi Fibrobacteres/Acidobacteria Firmicutes Fusobacteria Gemmatimonadetes Nitrospirae Omnibacteria Planctomycetes Proteobacteria Spirochaetes Thermodesulfobacteria Thermomicrobia Thermotogae Bacteria (singular, bacterium) are a major group of living organisms. ... Sexual reproduction is a union that results in increasing genetic diversity of the offspring. ... IT FEELS REALLY GOOD IF YOU IMATATE THE ANIMALS. LOL! “Mounting” redirects here. ... A gamete is a specialized germ cell that fuses with another gamete during fertilization (conception) in organisms that reproduce sexually. ... It has been suggested that Biparental zygote be merged into this article or section. ... Figure 1: Illustration of a bacterium with plasmids enclosed showing chromosomal DNA and plasmids. ... Transposons are sequences of DNA that can move around to different positions within the genome of a single cell, a process called transposition. ...


The genetic information transferred is often beneficial to the recipient cell. Benefits may include antibiotic resistance, other xenobiotic tolerance, or the ability to utilize a new metabolite.[5] Such beneficial plasmids may be considered bacterial endosymbionts. Some conjugative elements may also be viewed as genetic parasites on the bacterium, and conjugation as a mechanism was evolved by the mobile element to spread itself into new hosts. Antibiotic resistance is the ability of a micro-organism to withstand the effects of an antibiotic. ... A xenobiotic is a chemical which is found in an organism but which is not normally produced or expected to be present in it. ... A metabolite is the product of metabolism. ... An endosymbiont (also known as intracellular symbiont) is any organism that lives within cells of another organism, i. ... A parasite is an organism that lives in or on the living tissue of a host organism at the expense of it. ...

Contents

Mechanism

Schematic drawing of bacterial conjugation.

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 recipent cell. 4- Both cells recircularize their plasmids, synthesize second strands, and reproduce pili; both cells are now viable donors.

The prototype for conjugative plasmids is the F-plasmid, also called the F-factor.[1] The F-plasmid is an episome (a plasmid that can integrate itself into the bacterial chromosome by genetic recombination) of about 100 kb length. (One kb is one thousand base pairs) It carries its own origin of replication, called oriT.[4] There can only be one copy of the F-plasmid in a given bacterium, either free or integrated (two immediately before cell division). The host bacterium is called F-positive or F-plus (denoted F+). Strains that lack F plasmids are called F-negative or F-minus (F-). Image File history File links Download high-resolution version (694x813, 61 KB) Original work by Mike Jones for Wikipedia Overview of bacterial conjugation in 4 steps File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Image File history File links Download high-resolution version (694x813, 61 KB) Original work by Mike Jones for Wikipedia Overview of bacterial conjugation in 4 steps File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... For other uses, see Prototype (disambiguation). ... To meet Wikipedias quality standards, this article or section may require cleanup. ... Figure 1 : Schematic drawing of a bacterium with plasmids enclosed. ... Figure 1: A representation of a condensed eukaryotic chromosome, as seen during cell division. ... Genetic recombination is the process by which a strand of DNA is broken and then joined to the end of a different DNA molecule. ... Base pairs, of a DNA molecule. ... Base pairs, of a DNA molecule. ... The origin of replication (also called the replication origin) is a particular DNA sequence at which DNA replication is initiated. ...


Among other genetic information, the F-plasmid carries a tra and a trb locus, which together are about 33 kb long and consist of about 40 genes. The tra locus includes the pilin gene and regulatory genes, which together form pili on the cell surface, polymeric proteins that can attach themselves to the surface of F- bacteria and initiate the conjugation. Though there is some debate on the exact mechanism, the pili themselves do not seem to be the structures through which the actual exchange of DNA takes place; rather, some proteins coded in the tra or trb loci seem to open a channel between the bacteria. Short and long arms Chromosome. ... For other uses, see Gene (disambiguation). ... Image of bacteriological pili or fimbriae A pilus (Latin; plural : pili) is a hairlike structure on the surface of a cell, especially Gram-negative bacteria, a protein appendage required for bacterial conjugation. ... A representation of the 3D structure of myoglobin, showing coloured alpha helices. ...


When conjugation is initiated, via a mating signal, a relaxase enzyme creates a nick in one plasmid DNA strand at the origin of transfer, or oriT. The relaxase may work alone or in a complex of over a dozen proteins, known collectively as a relaxosome. In the F-plasmid system, the relaxase enzyme is called TraI and the relaxosome consists of TraI, TraY, TraM, and the integrated host factor, IHF. The transferred, or T-strand, is unwound from the duplex plasmid and transferred into the recipient bacterium in a 5'-terminus to 3'-terminus direction. The remaining strand is replicated, either independent of conjugative action (vegetative replication, beginning at the oriV) or in concert with conjugation (conjugative replication similar to the rolling circle replication of lambda phage). Conjugative replication may necessitate a second nick before successful transfer can occur. A recent report claims to have inhibited conjugation with chemicals that mimic an intermediate step of this second nicking event.[6] A nick is a point in a double stranded DNA molecule where there is no phosphodiester bond between adjacent nucleotides of one strand typically through damage or enzyme action. ... Rolling circle replication describes a process of DNA replication that can rapidly synthesize multiple copies of circular molecules of DNA, such as plasmids and the genomes of bacteriophages. ... Enterobacteria phage λ (lambda phage) is a temperate bacteriophage that infects Escherichia coli. ...


If the F-plasmid becomes integrated into the host genome, donor chromosomal DNA may be transferred along with plasmid DNA.[3] The certain amount of chromosomal DNA that is transferred depends on how long the bacteria remain in contact; for common laboratory strains of E. coli the transfer of the entire bacterial chromosome takes about 100 minutes. The transferred DNA can be integrated into the recipient genome via recombination. E. coli redirects here. ...


A culture of cells containing non-integrated F plasmids usually contains a few that have accidentally become integrated, and these are responsible for those low-frequency chromosomal gene transfers which do occur in such cultures. Some strains of bacteria with an integrated F-plasmid can be isolated and grown in pure culture. Because such strains transfer chromosomal genes very efficiently, they are called Hfr (high frequency of recombination). The E. coli genome was originally mapped by interrupted mating experiments, in which various Hfr cells in the process of conjugation were sheared from recipients after less than 100 minutes (initially using a Waring blender) and investigating which genes were transferred. A bacterium may undergo conjugation. ... In biology the genome of an organism is the whole hereditary information of an organism that is encoded in the DNA (or, for some viruses, RNA). ... Waring Products is a manufacturer of home and commercial kitchen appliances, laboratory equipment, and a variety of appliances and devices for the hotel industry. ...


Inter-Kingdom transfer

The nitrogen fixing Rhizobia are an interesting case, wherein conjugative elements naturally engage in inter-kingdom conjugation. Such elements as the Agrobacterium Ti or Ri plasmids contain elements can transfer to plant cells. Transferred genes enter the plant cell nucleus and effectively transform the plant cells into factories for the production of opines, which the bacteria use as carbon and energy sources. Infected plant cells form crown gall or root tumors. The Ti and Ri plasmids are thus endosymbionts of the bacteria, which are in turn endosymbionts (or parasites) of the infected plant. Diazotrophs are microorganisms that fix atmospheric nitrogen gas in to a more usable form such as ammonia. ... Soybean root nodules, each containing billions of Bradyrhizobium bacteria Rhizobia (from the Greek words riza = root and bios = Life) are soil bacteria that fix nitrogen (diazotrophy) after becoming established inside root nodules of legumes (Fabaceae). ... Ernst Haeckels presentation of a three-kingdom system (Plantae, Protista, Animalia) in his 1866 Generelle Morphologie der Organismen). ... Species Agrobacterium tumefaciens Agrobacterium rhizogenes áAgrobacterium is a genus of bacteria that causes tumors in plants. ... Opines are low molecular weight compounds found in plant crown gall tumors produced by the parasitic bacterium Agrobacterium. ... Binomial name Agrobacterium tumefaciens Smith & Townsend, 1907 Synonyms Bacterium tumefaciens Smith and Townsend 1907 Pseudomonas tumefaciens (Smith and Townsend 1907) Duggar 1909 Phytomonas tumefaciens (Smith and Townsend 1907) Bergey et al. ... Binomial name Agrobacterium rhizogenes (Riker et al. ...


The Ti and Ri plasmids are themselves conjugative. Ti and Ri transfer between bacteria uses an independent system (the tra, or transfer, operon) from that for inter-kingdom transfer (the vir, or virulence, operon). Such transfer creates virulent strains from previously avirulent Agrobacteria. Virulence refers to the degree of pathogenicity of a microbe, or in other words the relative ability of a microbe to cause disease. ...


See also

Transfection describes the introduction of foreign material into eukaryotic cells. ... Triparental mating is a form of Bacterial conjugation where a conjugative plasmid present in one bacterial strain assists the transfer of a mobilizable plasmid present in a second bacterial strain into a third bacterial strain. ...

References

  1. ^ a b Holmes RK, Jobling MG (1996). Genetics: Conjugation. in: Baron's Medical Microbiology (Baron S et al, eds.), 4th ed., Univ of Texas Medical Branch. ISBN 0-9631172-1-1. 
  2. ^ Lederberg J, Tatum EL (1946). "Gene recombination in E. coli". Nature 158: 558. 
  3. ^ a b Griffiths AJF, et al (1999). An Introduction to genetic analysis, 7th ed., San Francisco: W.H. Freeman. ISBN 0-7167-3520-2. 
  4. ^ a b Ryan KJ, Ray CG (editors) (2004). Sherris Medical Microbiology, 4th ed., McGraw Hill, p. 60–4. ISBN 0838585299. 
  5. ^ Holmes RK, Jobling MG (1996). Genetics: Exchange of Genetic Information. in: Baron's Medical Microbiology (Baron S et al, eds.), 4th ed., Univ of Texas Medical Branch. ISBN 0-9631172-1-1. 
  6. ^ Lujan SA, Guogas LM, Ragonese H, Matson SW, Redinbo MR (2007). "Disrupting antibiotic resistance propagation by inhibiting the conjugative DNA relaxase". PNAS 104: 12282-7. 

External links

  • Science project: Bacterial conjugation Transgenic poplars: Is horizontal gene transfer from Agrobacteria to endophytic bacteria possible?

  Results from FactBites:
 
Bacterial Gene Swapping in Nature (3153 words)
Conjugation was the first mechanism of gene transfer studied extensively as a way bacteria might disseminate genetic material in nonlaboratory arenas.
Thus, even if they travel to a new bacterial host, they do not become a stable part of that host's genome; chromosomes are invariably copied and distributed to new generations of bacterial cells whenever a parent cell reproduces itself, but plasmids are not reproduced consistently when cells divide.
Although conjugation was the first mechanism of bacterial gene transfer to be studied extensively in the environment, it was not the earliest to be identified.
Genetic Exchange Utilizing Microbial Donors or Vectors (2249 words)
Most bacterial cells need to be at a particular stage in their growth cycle or under a particular growth regimen in order to be transformed.
Conjugation begins with the extrusion of a sex pilus; the tip of the sex pilus adheres to the outer membrane of Gram-negative cell walls.
A bacterial cell containing a F plasmid integrated into the bacterial DNA is termed a Hfr (high frequency of recombination) cell.
  More results at FactBites »

 
 

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