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| Genetic Modification of Bacteria |
Bacteria - the first organisms to be genetically engineered - are used for replicating and altering genes that are subsequently introduced into plants or animals. Bacterial systems lend themselves to genetic manipulation in part because of their rapid reproduction rates. It is easy to produce a genetically identical population - a clone of bacteria - all containing the gene of interest in a short period. The cells can then be lysed and DNA can be isolated in short order. Bacteria are routinely used to produce non-bacterial proteins. An example is the production of purified proteins for vaccine use. Such proteins can be safer and as effective as vaccines that contain killed or attenuated (weakened) pathogens. Genetic engineering can also produce extensive changes in the bacterium's metabolism. For example, bacteria can be provided with several genes, encoding enzymes that allow the production of fuel alcohol from wood.
Researchers have taken advantage of nature to modify bacteria. Plasmids are small, circular, self-replicating, extrachromosomal pieces of DNA that occur naturally. A plasmid can encode a protein that offers its host a selective advantage. For example, a plasmid that encodes an antibiotic allows its host bacterium to thwart competing microbes. Alternately, a bacterium might possess a plasmid that encodes antibiotic resistance. Plasmids are readily isolated from bacterial cells and can be altered in vitro by inserting or deleting specific sequences of DNA. Because they can be used to create clones of genes, plasmids are called cloning vectors.