Horizontal gene transfer in prokaryotes

Template:Stub Horizontal gene transfer is common among bacteria, even very distantly-related ones. This process is thought to be a significant cause of increased drug resistance; when one bacterial cell acquires resistance, it can quickly transfer the resistance genes to many species. Enteric bacteria appear to exchange genetic material with each other within the gut in which they live. There are three common mechanisms for horizontal gene transfer:

• Bacterial transformation , the genetic alteration of a cell resulting from the introduction, uptake and expression of foreign genetic material, generally DNA(see this animation with audio explanation). This process is relatively common in certain naturally transformable bacteria, but less common in eukaryotes. Transformation is often used as a biotechnology to insert novel genes into bacteria for scientific research experiments, or for industrial or medical applications. See also molecular biology and biotechnology.
• Transduction, the process in which bacterial DNA is moved from one bacterium to another by a bacterial virus (a bacteriophage, commonly called a phage).
• Bacterial conjugation, a process in which a living bacterial cell transfers genetic material through cell-to-cell contact (see the animation conjugation in Escherichia coli).

History of horizontal gene transfer in prokaryotes

• The concept of horizontal gene transfer starting in 1946, when Lederberg and Tatum discover genetic conjugation in Escherichia coli K-12 , and this process was later shown to be carried out by the first recognized plasmid, fertility factor F. In 1951, Joshua and Ester Lederberg , together with Zinder and Lively report the first evidence of bacterial genetic recombination in Salmonella that was later shown to be caused by bacteriophage mediated transduction of bacterial chromosome fragments, which is the term used for horizontal movement of genes carried in bacterial viruses. Joshua Lederberg's discovery of conjugation was famously desribed by Salvador Luria (1947) as " to be among the most fundamental advances in the whole history of bacteriological science", giving great prominence to studies of horizontal gene transfer during the 1950s, 60s and 70s . Transduction is currently recognized as a major route for horizontal gene movement in bacteria, and plasmid mediated bacterial conjugation is now known to be promiscuous process that enables DNA to transfer across taxonomic species, genera, phyla and domains.

Plasmids, episomes, mobile DNA in microorganisms

• The existence of several genetic structures that can insert within bacterial chomosomes, based on observation of the bacteriophage lambda and fertility factor in 1958 F lead F. Jacob and E. L. Wollman to coin the term episome for DNA elements that have alternate modes of existence within the cell, either in the chromosome, or as autonomously resplicating stuctures. Subsequent study of these phenomenon revealed numerous occurences of mobile DNA in a wide range of organisms (such as the presence of insertion sequence (IS) "jumping genes" that allow F plamid insertion in the chromosome) and widespread horizontal gene transfer involving by bacteriophage, plasmids and mobile DNA in general.

• Tomoichiro Akiba and Kunitaro Ochia discover mobile antibiotic resistance genes in bacteria , and the horizontal transfer is later shown to mediated by plasmids that inject DNA promiscuously into other cells .

• James Shapiro discovers that spontaneously occuring insertions of large inserts of extra DNA can causes mutationss in the galactose genes of the bacterium Escherichia coli . This discovery ultimately led to the discovery of mobile inserton sequences (IS).

References

Further reading

• Snyder, L. and Champness, W. (2003) Molecular Genetics of Bacteria, @nd Edition, ASM Press Washington DCISBN 1-55581-204-X

External links

• Bacterial transformation
• Lateral gene transfer