Word: plasmids
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Dates: during 1970-1979
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...Thus their ability to acquire new and possibly advantageous genes would seem to be highly limited. But the tiny creatures have devised a cunning alternative. Besides their single, large, ringed chromosome (which is the repository of most of their genes), they possess much smaller closed loops of DNA, called plasmids-which consist of only a few genes. This extra bit of DNA-genetic small change, as it has been dubbed-serves a highly useful purpose. When two bacteria brush against each other, they sometimes form a connecting bridge. During such a "conjugation," a plasmid from one bacterium may be passed...
These natural transfers can be crucial to the survival of the bacterium. It is through new plasmids, for example, that bacteria like Staphylococcus aureus have become resistant to penicillin. The plasmid acquired by the staph bug contained a gene that directs the production of a penicillinase, an enzyme that cracks apart invading penicillin molecules, making them ineffective. Different plasmids, sometimes passed from one bacterium to another, can order up still another kind of chemical weapon, a so-called restriction enzyme, which can sever the DNA of an invading virus, say, at a predetermined point...
...very large safety factor is added by the provision in the present Guidelines for biological containment. All work with mammalian DNA must be carried out only in an EK2 strain, which has a drastically impaired ability to multiply, or to transfer its plasmid, except under very special conditions provided in the laboratory...
...inability of an EK2 strain to multiply in the gut would be sufficient to ensure its rapid disappearance, even if it did not rapidly commit suicide. The important question, requiring extensive investigation, is not the rate of suicide of the EK2 strain but the chance of transfer of its plasmid to a better adapted strain, before disappearance of the EK2 host...
Finally-after several experiments -Chakrabarty discovered that irradiating the host organisms with ultraviolet light after plasmid transfer induced a genetic cross-linking that fixed the new genes in place and produced stable bacteria with a healthy appetite for oil. The new microbe, to which Chakrabarty gives the jawbreaking description "multi-plasmid hydrocarbon-degrading pseudomonas," can digest about two-thirds of the hydrocarbons involved in an oil spill. The new microbes have been tested only in the laboratory, where a pinch of microbes will eat an eyedropper of oil in a matter of days. This may seem slow...