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Recombinant Microbes: Modified Bacteria and Viruses

المؤلف:  Barry Chess

المصدر:  Talaros Foundations In Microbiology Basic Principles 2024

الجزء والصفحة:  12th E , P 320-321

2026-07-22

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One of the first practical applications of recombinant DNA was the creation of a genetically altered strain of the bacterium Pseudomonas syringae. The wild strain ordinarily contains an ice formation gene that promotes ice or frost formation on moist plant surfaces. Genetic alteration of the frost gene using recombinant plasmids created a different strain that could prevent ice crystals from forming. A commercial product called Frostban was developed but never marketed due to the controversy arising from its re lease into the environment. In another trial, a strain of Pseudomonas fluorescens was engineered with the gene from a bacterium (Bacillus thuringiensis) that codes for an insecticide (Bt toxin). These recombinant bacteria are released to colonize plant roots and help destroy invading insects. All releases of recombinant microbes must be approved by the U.S. Environmental Protection Agency and are closely monitored.

Although primarily known for its ability to cause colds, the adenovirus has been bioengineered to attack and destroy cancer cells. These oncolytic adenoviruses have been altered so that their host range consists exclusively of cells that produce cancer-specific proteins. By simply infecting a cancerous cell and replicating, the engineered virus will eventually lyse and kill the cell. Although this procedure is not yet approved for use in humans, this novel use of viral vectors speaks to the potential of genetically engineered viruses. This technology is currently used to engineer viruses to deliver genes into animals and humans (see figure 1).

Process Fig1 Ex vivo gene therapy. (1) Stem cells are removed from the bone marrow of a patient with a genetic defect. (2) A normal version of the gene is isolated from a healthy subject, cloned, and inserted into a viral vector. (3) The virus is used to infect the patient’s cells in the laboratory. The viral vector inserts the healthy version of the gene into the genome of the patient. (4) The transfected cells are infused into the patient, where they move to the bone marrow. The transfected cells will continue to multiply in the bone marrow, producing protein from the corrected gene.

In 2010, a milestone was reached when Craig Venter’s laboratory team created an entirely new bacterial species by inserting a completely synthesized genome of artificial origin into Mycoplasma genitalium. The new species, named Mycoplasma laboratorium, contains the smallest functional genome of any bacterium, with 382 genes of around 1.1 million base pairs. So far the scale of this experiment is small—a single-celled organism— but its implications are large. The growing power of genetic engineering and synthetic biology has fostered a deeper examination of the bioethics involved in modifying the genetics of organ isms (10.1 Making Connections).