Genetically modified bacteria
Genetically modified bacteria are microorganisms that have been altered through genetic engineering techniques to incorporate DNA from other organisms. This process began with key discoveries in the mid-20th century, including the demonstration of gene transfer among bacteria and the development of restriction enzymes, which allow scientists to cut and splice DNA from various sources. These modified bacteria often utilize plasmids—small, circular DNA molecules that can carry genes of interest, such as those for antibiotic resistance or the production of human proteins like insulin.
One notable application of genetically modified bacteria is in medicine, where bacteria like Escherichia coli have been engineered to produce human insulin, providing a reliable and less allergenic alternative to animal-sourced insulin. Additionally, genetically modified bacteria are used as vectors to introduce genes into plants, enhancing traits like pest resistance. The bacterium Agrobacterium tumefaciens, for example, has been instrumental in integrating new genetic material into plant cells.
While the use of genetically modified organisms has sparked public debate regarding environmental and health implications, regulatory frameworks have evolved to facilitate their development and application. By 2002, numerous permits for field tests of genetically altered plants and microorganisms had been issued, highlighting the growing acceptance and integration of biotechnology in agriculture and medicine.
Genetically modified bacteria
Categories: Bacteria; biotechnology; economic botany and plant uses; genetics
The ability to genetically engineer bacteria is the outcome of several independent discoveries. In 1944 Oswald Avery and his coworkers demonstrated gene transfer among bacteria using purified DNA (deoxyribonucleic acid), a process called transformation. In the 1960’s the discovery of restriction enzymes permitted the creation of hybrid molecules of DNA. Such enzymes cut DNA molecules at specific sites, allowing fragments from different sources to be joined within the same piece of genetic machinery.
Restriction enzymes are not specific in choosing their target species. Therefore, DNA from any source, when treated with the same restriction enzyme, will generate identical cuts. The treated DNA molecules are allowed to bind with one another, while a second set of enzymes called ligases are used to fuse the fragments together. The recombinant molecules may then be introduced into bacteria cells through transformation. In this manner, the cell has acquired whatever genetic information is found in the DNA. Descendants of the transformed cells will be genetically identical, forming clones of the original.
Bacterial Plasmids
The most common forms of genetically altered DNA are bacterial plasmids, small circular molecules separate from the cell chromosome. Plasmids may be altered to serve as appropriate vectors (carriers of genetic material) for genetic engineering, usually containing an antibiotic resistance gene for selection of only those cells that have incorporated the DNA. Once the cell has incorporated the plasmid, it acquires the ability to produce any gene product encoded on the molecule.
The first such genetically altered bacteria used for medical purposes, Escherichia coli, contained the gene for the production of human insulin. Prior to creation of the insulin-producing bacterium, diabetics were dependent upon insulin purified from animals. In addition to being relatively expensive, insulin obtained from animals produced allergic reactions among some individuals. Insulin obtained from genetically altered bacteria is identical to that of human insulin. Subsequent experiments also engineered bacteria able to produce a variety of human proteins, including human growth hormone, interferon, and granulocyte colony-stimulating factor.
Use in Plants
Genetically modified bacteria may also serve as vectors for the introduction of genes into plants. The bacterium Agrobacterium tumefaciens, the cause of the plant disease called crown gall, contains a plasmid called Ti. Following infection of the plant cell by the bacterium, the plasmid is integrated into the host chromosome, becoming part of the plant’s genetic material. Any genes that were part of the plasmid are integrated as well. Desired genes can be introduced into the plasmid, promoting pest or disease resistance.
In April of 1987 scientists in California sprayed strawberry plants with genetically altered bacteria to improve the plants’ freeze resistance, marking the first deliberate release of genetically altered organisms in the United States to be sanctioned by the Environmental Protection Agency (EPA). The release of the bacteria climaxed more than a decade of public debate over what would happen when the first products of biotechnology became commercially available. Fears centered on the creation of bacteria that might radically alter the environment through elaboration of gene products not normally found in such cells. Some feared that so-called super bacteria might be created with unusual resistance to conventional medical treatment. Despite these concerns, approval for further releases of genetically altered bacteria soon followed, and the restrictions on release were greatly relaxed. By 2002, permits for field tests of hundreds of genetically altered plants and microorganisms had been granted.
Bibliography
Dale, Jeremy W. Molecular Genetics of Bacteria. 3d ed. New York: John Wiley, 1998. Uses a molecular approach to introduce students to bacterial genetics. Provides clear explanations of techniques and terminology.
Levin, Morris A., ed. Engineered Organisms in Environmental Settings: Biotechnological and Agricultural Applications. Boca Raton, Fla.: CRC Press, 1996. Overview of environmental applications of genetically modified organisms; describes their releases into the environments and their observed effects.
Miesfeld, Roger L. Applied Molecular Genetics. New York: John Wiley, 1999. Discusses key biochemical and cell biological principles behind commonly used applications of molecular genetics, using clear terms and well-illustrated flow schemes. Includes references and a list of Web sites.