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Introduction of Recombinant DNA-Engineered Organisms Into the Environment: Key Issues (1987)

Chapter: The Potential Hazards of R-DNA-Engineered Organisms into the Environment: Separating Real from Hypothetical Problems

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Suggested Citation:"The Potential Hazards of R-DNA-Engineered Organisms into the Environment: Separating Real from Hypothetical Problems." National Research Council. 1987. Introduction of Recombinant DNA-Engineered Organisms Into the Environment: Key Issues. Washington, DC: The National Academies Press. doi: 10.17226/18907.
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Suggested Citation:"The Potential Hazards of R-DNA-Engineered Organisms into the Environment: Separating Real from Hypothetical Problems." National Research Council. 1987. Introduction of Recombinant DNA-Engineered Organisms Into the Environment: Key Issues. Washington, DC: The National Academies Press. doi: 10.17226/18907.
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Page 13
Suggested Citation:"The Potential Hazards of R-DNA-Engineered Organisms into the Environment: Separating Real from Hypothetical Problems." National Research Council. 1987. Introduction of Recombinant DNA-Engineered Organisms Into the Environment: Key Issues. Washington, DC: The National Academies Press. doi: 10.17226/18907.
×
Page 14
Suggested Citation:"The Potential Hazards of R-DNA-Engineered Organisms into the Environment: Separating Real from Hypothetical Problems." National Research Council. 1987. Introduction of Recombinant DNA-Engineered Organisms Into the Environment: Key Issues. Washington, DC: The National Academies Press. doi: 10.17226/18907.
×
Page 15
Suggested Citation:"The Potential Hazards of R-DNA-Engineered Organisms into the Environment: Separating Real from Hypothetical Problems." National Research Council. 1987. Introduction of Recombinant DNA-Engineered Organisms Into the Environment: Key Issues. Washington, DC: The National Academies Press. doi: 10.17226/18907.
×
Page 16
Suggested Citation:"The Potential Hazards of R-DNA-Engineered Organisms into the Environment: Separating Real from Hypothetical Problems." National Research Council. 1987. Introduction of Recombinant DNA-Engineered Organisms Into the Environment: Key Issues. Washington, DC: The National Academies Press. doi: 10.17226/18907.
×
Page 17

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The Potential Hazards of T e ability of R-DNA techniques to expand the range f organisms among which genetic exchanges can be made and to increase the rapidity and precision of R-ONA-Engineered Organisms genetic manipulations has raised the number of practical applications for genetically modified organisms. But concerns have been expressed about the use of these tech­ in the Environment: niques and about the possibility that their very availability will increase the frequency and scale of introductions of modified organisms into the environment The two broad categories of Separating Real from concerns are whether distant genetic transfers and the use of R-DNA technology for genetic manipulations are inherendy hazardous and whether the widespread introduction of organ­ Hypothetical Problems isms containing R-DNA can cause major ecological disruptions. Some of the concerns are substantial; others are not war­ ranted. To avoid the two extremes of paralyzing overregulation and inattention to significant potential hazards, the issues must be assesse d in the light of scientific knowledge and accumu­ lated experience. T his section deals only with those questions that can be answered on that basis. It draws on our experience, largely in laboratory and agricultural applications, although future uses of R-ONA-engineered organisms will include the leaching of ores and degradation of pollutants, as well as agri­ cultural applications outside our current experience (Gillett et al, 1986). Nonetheless, for all applications the appropriate focus of concern should be the properties of the engineered organism, not the method by which it was produced. Some argue that all possible genetic combinations have occurred during evolutionary history and that organisms with

13 novel traits therefore cannot be produced by R-DNA manipula­ exchange genes in nature. But are such transfers truly novel? tions. However, it is probable that only a small fraction of Genetic exchanges brought about by unconventional, nonsex­ genetic combinations have ever arisen, and most would have ual means occur often in nature. Recent advances in molecular appeared in environments unfavorable to the survival of the biology have revealed that the cells of most organisms can organism. It is quite likely that R-DNA techniques will permit assimilate and incorporate genetic material from almost any the introduction of genes that will confer traits novel to a given source, and there is evidence that such exchanges have some­ organism in a contemporary environment T herefore, evolu­ times occurred naturally. They are usually unproductive be­ tionary arguments cannot be used to assen categorically that cause the genetic signals for gene expression function only engineered organisms are risk free. Rather, the evaluation of the when the recipient organism is closely related to the donoJ: To risks associated with a particular introduction should be based solve this problem, researchers have learned to alter the signals on the properties of the engineered organism and its target that enable a gene to be expressed in the recipient organism. environment Nature has done this too. For example, strains of the crown gall bacterium (Agrobacterium tumefaciens) carry genes that can be Is It Inherendy Danguous to U� expressed only in plant cells. The bacteria have developed a R-DNA Techniques to Move Genes Between mechanism for transferring certain genes to plant cells and for Unrelated Organisms? directing the plant cells to express the genes to make com­ Are R-DNA technologies inherendy hazardous? They have pounds that the bacterium can use as a source of food and been used in hundreds of laboratories for more than a decade energy. Thus, gene transfers among different types of organisms to produce R-ONA-engineered organisms on a small experi­ do occur in nature. mental scale and more recendy on a large commercial scale in Are genetic transfers between unrelated organisms more industrial fermenters. During that time, the transfer of innu­ likely to give rise to problem organisms than genetic transfers merable genes between very different kinds of organisms has between closely related organisms? Also, is there scientific jus­ created untold numbers of individual transgenic organisms. No tification for designating as "novel" an organism containing a hazard peculiar to the use of R-DNA techniques has yet sur­ gene, or a small number of genes, from another species? Many faced, and there is a broad consensus among biologists that thousands of distant genetic transfers have been carried out R-DNA techniques are safe. with R-DNA techniques, and the organisms with the new genes Considerable concern is voiced over the use of R-DNA tech­ have the predicted properties: they behave like the parent niques to move genes between organisms that do not generally organism, but exhibit the new trait or traits expected to be

associated with the introduced gene or genes. Thus, an parent organism in their reproductive and growth charac­ R-ONA modified organism is not a "novel" organism; rathet; it teristics, and they are often at a disadvantage with respect to is like a breeder's new variety of a flowet Occasionally, unex­ their parents in their ability to survive and to reproduce. Thus, pected changes occur, but these have been detrimental to the it is not valid to regard all R-ONA-engineered organisms as organisms, making them less able to survive. nonnative. No evidence based on laboratory observations indicates that Species invasions are among the most serious problems con­ unique hazards attend the ttansfer of genes between unrelated fronting environmental managers, and the nonnative or alien organisms. Furthermore, there is no evidence that a gene will species model of introduction does provide a sound basis for conven a benign organism to a hazardous one simply because exttapolation when the introduced species is not native to its the gene came from an unrelated species. The strong implica­ target environment But many of the currendy proposed agri­ tion is that neither the source of the gene nor the method by cultural applications of R-ONA-engineered organisms will which it is introduced warrants concern in assessing R-ONA­ involve reintroducing modified organisms into the same or a engineered organisms. similar environment from which they were taken, so they are not analogous to the introduction of a nonnative species. Are R-ONA-Engineered Organisms Uke Nonnative Organisms? Will the Use ofR-DNA Techniques An analogy is frequendy made between the potential conse­ Accidentally Create New Plant Pests? quences of introducing R-ONA-engineered organisms into the It has been suggested that the genetic engineering of crop environment and the serious ecological disruptions that have plants might increase the potential for creating new pest plants, been caused by the introduction of certain nonnative or alien or "super-weeds:' Weeds differ from crop plants in a number of organisms, such as the gypsy moth, the starling. and the kudzu ttaits. These include vigorous growth, production of large num­ vine. This comparison is based to some extent on the assump­ bers of seeds, production of seeds that are long-lived and ger­ tion that R-ONA modifications can change the properties of an minate readily. the capacity for either self- or crosspollination, organism in a wholly unpredictable way that will increase its and a mechanism for rapid dispersal. One published summary ability to affect the environment adversely. As discussed in of the characteristics of an ideal weed includes 12 ttaits, most detail in the preceding section, experience to date indicates that of which are determined by many genes (Keelet; 1985). · this is atremely unlikely. Engineered organisms, whether pro­ Although few weeds possess all these ttaits, most successful duced by ttaditional or R-ONA manipulations, resemble the ones have a cluster of several. A single mutation can signifi-

15 candy enhance the potential of a given plant to become a weed, environmental conditions outside the host Together with the but the plant must already possess a number of the characteris­ need to compete effectively with many other microorganisms tics conducive to weedlike behavi01: Moreover; although the for survival, these traits form an impressive array of require­ mechanisms by which weeds have evolved will continue to ments for pathogenicity. The possibility that minor genetic operate, there is no evidence that plants engineered with modifications with R-ONA techniques will inadvertently con­ R-ONA will behave differendy from plants produced by tradi­ ven a nonpathogen to a pathogen is therefore quite remote. tional breeding procedures. In dealing with a pathogen or with properties related to path­ Care must be taken when genes conferring traits such as ogenicity. different considerations apply. For example, an aviru­ herbicide resistance are inttoduced into plants that can out­ lent (nonpathogenic) strain of a pathogen can be convened cross with closely related wild and weedy species. Caution into a virulent strain by a small genetic change, because the must also be exercised in the genetic manipulation of weeds, transition can be controlled by either a single gene or a small but the probability that R-ONA modification can inadvertently number of genes. A change in a single gene in the fungal conven a crop plant to a noxious weed is negligible and war­ pathogen that causes black stem rust of wheat, for instance, can rants litde concern. alter the range of wheat varieties it can attack. However; this is a genetic change in a pathogen that is able to infect some vari­ Can R-DNA Accidentally Convert a eties, but is nonpathogenic to others; it does not represent the Nonpathogen to a Pathogen? conversion of a nonpathogen into a pathogen. Among the dangers envisioned in R-ONA genetic engineering of microorganisms is the inadvertent conversion of a non­ Can lnttoduced Genes Spread in a pathogen into a new, virulent pathogen. How valid is this con­ Microbial Population? cept? It is important to recognize that virulent pathogens of Concern has been expressed over the possibility that an humans, animals, and plants possess a large number of varied inttoduced gene could move from a harmless microorganism characteristics that in total constitute their pathogenic poten­ to a weak pathogen by natural mechanisms and increase the tial. The traits contributing to pathogenicity include the ability pathogenicity of the lane�: Many studies have indicated that to attach to specific host cells, to resist a wide range of host populations of bacteria characteristically do not exchange chro­ defense systems, to form toxic chemicals that kill cells, to pro­ mosomal DNA (Selander tt aL, 1987). Yet it must be recognized duce enzymes that degrade cell components, to disseminate that certain mobile genetic elements can spread widely among readily and invade new hosts, and to survive under adverse unrelated populations in the presence of a specific selection

16 pressure. It is not the introduction of a microorganism with a Thus, the weight of evidence indicates that the transfer of special genetic trait that results in population explosions, but large segments of genetic material rarely leads to its persistence selection for that special trait, often as a consequence of the in a population unless strong selection pressure is applied. application of manufactured chemicals or drugs. Movement of Funhermore, even when some of the genes required for plasmids that cany genes for antibiotic resistance is a well­ pathogenicity are on mobile genetic elements, they have a low recognized example of such gene mobility. probability of dissemination to related bacteria with a comple­ Transfer between microorganisms of plasmids, transposons, mentary array of genes for pathogenicity. and an even lower and other mobile genetic elements has been central to the probability of transfer to unrelated species of bacteria. evolution of pathogenic traits. The pathogenic types within the common bacterial species Escherichia coli all cany genes for Will R-ONA-Engineered Microorganisms pathogenicity on mobile plasmids or bacteriophages. It might Alter Soil Microbial Communities? be surmised from these observations that the wide-ranging Nonpathogenic soil microorganisms from different regions spread of genetic information is proceeding at a high rate in might be used in managed ecosystems, and there is concern natural populations of microorganisms. But the fact that certain about potential negative consequences for the native microbial components essential for pathogenicity are carried on plasmids community. Such concern is not necessarily unique to the use and bacteriophages does not mean that genetic traits for viru­ of R-ONA-engineered organisms, but is enhanced by the pros­ lence spread indiscriminately in populations of nonpathogens, pect that R-DNA techniques will result in the production and converting them to pathogens. On the contrary, transfer of a introduction of many more soil microorganisms than in the plasmid with the genetic information that codes for an entero­ past. toxin is not adequate to conven the majority of normal E. coli It has been suggested that little or no experience with such strains to pathogens. The reason is clear: pathogenicity introductions is available to provide guidance. In fact, although depends on many genes, as indicated earlier Even though little has been done with aquatic microbial communities, a many determinants of pathogenicity are on plasmids, only a substantial body of data exists on the worldwide use of small subset of bacteria in natural populations have all the nitrogen-fixing soil bacteria in the genus Rhizobium. These bac­ traits essential to the "pathogenic personality." That is true not teria have been used since the 1890s, and more recently only for the major pathogenic genera in the enteric group of nitrogen-fixing organisms in the genus Frankia have also been bacteria, but also for most of the other bacteria of medical and used. To our knowledge, their widespread use has not resulted agricultural importance. in detectable adverse effects on the microbial balance in the

l7 diverse soils into which they have been introduced, even when populations is a familiar example, as are algal blooms in pol­ the soils have been quite different from those from which these luted waters. Such major population shifts are generally attrib­ bacteria were originally isolated. Similarly. improved strains of utable to selection by environmental factors, such as an some soil fungi that establish a symbiotic relationship with the increase in chemical nutrients or the widespread use of fertil­ roots of many species of pines and other trees (mycorrhizae) izers, insecticides, pesticides, or antibiotics. Thus, observed have been introduced into forest nurseries without evidence of major shifts in microbial communities in soils mainly reflect damaging effects. alterations in environmental factors rather than solely the bio­ This record reflects the stabilizing or buffering capacity and logical or ecological characteristics of the introduced organ­ resistance to change that have been attributed to the tremen­ isms. In the case of introduced pathogens, the prevalence and dous abundance and diversity of life in soils, as each gram of susceptibility of hosts are also of major importance. Thus, soil includes nematodes, protozoa, fungi, and insects, as well as when considering the introduction of a microorganism, not 10 million-100 million bacteria, belonging to many different only must the biological and ecological properties of the organ­ genera. It should also be noted that seeds, cuttings, and propa­ ism be weighed, but also the environment into which it will be gative material such as seed potato tubers with their attendant introduced. microflora and microfauna have been and are constandy being moved from one region to another with no evidence of major problems affecting the soil microbiology. Thus, nonpathogenic soil microorganisms from diverse environments have been introduced on a large scale without evidence of negative impacts. Microorganisms have also been widely used as insect control agents. For example, Badllus thuringiensis, a bacterium that pro­ duces a protein toxic to some insects, has been used on a large scale to control gypsy moths and other insects, and no adverse effects on indigenous microorganisms have been attributed to this procedure. Nonetheless, major shifts in microbial commu­ nities have occurred under certain circumstances. The recent rapid rise in antibiotic-resistant microorganisms in human

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