Chapter 24
Safety Issues in Perspective Winston J. Brill
Biotechnology in Agricultural Chemistry Downloaded from pubs.acs.org by UNIV OF TEXAS AT EL PASO on 11/04/18. For personal use only.
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The appropriate l e v e l of regulatory scrutiny f o r f i e l d testing recombinant organisms should be based on our extensive experience with t r a d i t i o n a l a g r i c u l t u r a l practices. When safety issues are examined from a s c i e n t i f i c point of view, it can be concluded that the risk from recombinant organisms i s no different than the risk that has been associated with t r a d i t i o n a l plant or microbial genetic research and practices of many decades.
Plants or microorganisms that seem, from laboratory or greenhouse experiments, to be p o t e n t i a l l y useful i n agriculture must be f i e l d tested to check the relevance of these r e s u l t s . There are innumerable cases of exciting greenhouse findings not reproducible i n the f i e l d . A l l of the many changing environmental factors a plant experiences i n the f i e l d cannot be replicated by greenhouse experiments. Therefore, small-scale f i e l d testing early i n a project i s essential i f organisms are to be considered f o r use i n agriculture. This has been the case f o r organisms not genetically altered as well as f o r genetically modified organisms. Federal agencies are now deciding how to regulate recombinant plants and microorganisms to ensure that t h e i r release into the environment w i l l not create health or environmental problems. This paper w i l l address the potential f o r problems that may arise from releasing recombinant organisms. The chance of this technology producing a serious problem should be compared to problems we now accept from current practices.
PLANTS An experiment to improve crop plants by adding foreign genes should have less of a chance f o r problems than t r a d i t i o n a l breeding experiments. Breeders routinely cross cultivated plants with wild, exotic r e l a t i v e s . U n t i l the results of the cross have been 0097-6156/87/0334-0297$06.00/0 © 1987 American Chemical Society
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analyzed, the breeder cannot predict progeny c h a r a c t e r i s t i c s , which are the result of random mixing of thousands of genes. Breeders are not concerned that a plant derived from such a cross w i l l become a problem weed because extensive, world-wide experience with these types of crosses has not produced plants that are d i f f i c u l t to control. Scientists know that weeds such as dandelion, pigweed, or kudzu are problems because they have a number of properties that enable them to predominate and compete against other plants i n t h e i r environment. Such problem weeds probably require dozens, i f not hundreds, of s p e c i f i c genes to maintain t h e i r "weedy" character. Therefore, many specialized genes are required to convert a nonweedy crop plant into a weed that would cause a serious problem. Compared to breeding a crop with exotic species, a genetic engineering experiment with that crop i s very s p e c i f i c . The introduced foreign genes probably are well characterized, plant modifications are not due to random mixing of genes, and the properties of the plant are quite predictable. There seems to be chance that expression of several characterized genes added to a crop plant for the purpose of making i t more valuable w i l l create weed that could cause problems of the magnitude of a kudzu. Even several uncharacterized genes are added to the crop plant, the chance that they w i l l interact i n a way to make that plant become problem weed should be s u f f i c i e n t l y low to become a negligible concern.
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Current practice with chemicals creates large populations of genetically altered organisms. For instance, herbicides added to m i l l i o n s of acres year a f t e r year produce mutant weeds that become resistant to the chemical. S i m i l a r l y , i n s e c t i c i d e use results i n i n s e c t i c i d e - r e s i s t a n t insects. Thus, chemicals cause uncharacterized changes i n problem organisms. By comparison, genetic engineering w i l l create characterized changes i n safe organisms. There i s no concern that genetic events from use of chemical pesticides w i l l cause problems i n environments lacking the applied chemical ( p e s t i c i d e ) , even though the g e n e t i c a l l y altered weed or insect readily move to chemical-free environments. Many groups applying recombinant DNA technology to plants are t r y i n g to create plants which are resistant to pests or produce t h e i r own herbicides. Thus, future agriculture w i l l be f a r less dependent on synthetic organic chemicals as pesticides and herbicides. Laboratories have introduced the B a c i l l u s thuringiensis toxin into plants. This toxin i s a protein that s p e c i f i c a l l y k i l l s certain c a t e r p i l l a r s . It i s nontoxic to man, bees, and other insects and has been a commercial product, applied to vegetables and f o r e s t s , for many years. Unlike the s i t u a t i o n with chemical i n s e c t i c i d e s , toxin-resistant insects do not readily appear. If the toxin gene i s suitably expressed i n plants, then such plants are p o t e n t i a l l y resistant to many troublesome insects. Other toxins s p e c i f i c to a d i f f e r e n t range of insects also are known. Such protein toxins w i l l cause fewer problems to man and the environment than currently used chemical p e s t i c i d e s .
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As i s the case with t r a d i t i o n a l breeding practices, there w i l l be problems caused by recombinant plants. Addition of a foreign gene may simultaneously give the plant an undesirable property (e.g. greater s u s c e p t i b i l i t y to drought). Undesirable features usually are detected during experimental f i e l d t r i a l s . If these negative characteristics cannot be eliminated from the plant, the new variety w i l l not be useful commercially. If a problem appears only a f t e r commercial introduction, the variety w i l l rapidly be replaced by a new one. Breeders are trained to be a l e r t f o r these types of problems. Because the genetic a l t e r a t i o n i n a recombinant plant i s well-controlled, the l i k e l i h o o d of a problem i s f a r less than i n standard breeding practices.
MICROORGANISMS Because microorganisms (bacteria and fungi) are i n v i s i b l e , can readily be transported, and are known to cause plant and animal diseases, there seems to be a greater concern f o r recombinant microorganisms than f o r recombinant plants released to the environment. In the case of microorganisms known to be pathogens, special care about release c e r t a i n l y i s warranted; however, a recombinant pathogen probably i s less dangerous than i t s unmodified parent due to the increased genetic load by the added recombinant gene. Regulations that s a t i s f a c t o r i l y govern release of pathogens (e.g. f o r biocontrol) should be relevant to recombinant pathogens· There are no federal regulations that govern experimental release of native microorganisms that are considered to be safe. Since the turn of the century, hundreds of different microbial products have been sold. Therefore, thousands of experimental inoculants have been f i e l d tested. These inoculants include bacteria to f i x nitrogen, algae to f e r t i l i z e the s o i l , bacteria to stimulate plant growth, and fungi to increase phosphorus uptake by plants. In many cases, mutant strains have been u t i l i z e d . There has not been a single problem that as gotten out of control through these practices. A recombinant microorganism used f o r agriculture i s expected to contain one or several characterized foreign genes. These genes should not create problem animal or plant pathogens (ones that could e f f i c i e n t l y spread disease) from non-pathogenic microorganisms. Studies with animal and plant pathogens have shown that many s p e c i f i c interacting genes are required f o r the organism to damage i t s host, maintain pathogenesis genes and t r a v e l between hosts. It seems v i r t u a l l y impossible that an experiment designed to improve plant growth with microorganisms modified by recombinant DNA technology w i l l give the microorganism a l l of these s p e c i f i c "pathogenesis" genes. With standard laboratory genetic techniques that have been i n common use f o r decades, there has been no example of a safe microbe being genetically altered to become a problem pathogen.
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Experience i n the chemical industry has sensitized us to be a l e r t for serious unexpected problems. Bhopal, Three Mile Island and Love Canal are examples. In the case of chemicals known to be toxic, a dangerous s i t u a t i o n i s p o t e n t i a l l y present during manufacture, use, transportation, storage or disposal of the chemical. In the case of recombinant microorganisms p o t e n t i a l l y useful to agriculture, there i s no apparent danger; therefore, a s p i l l or spread of the organism would not create a problem. Chemicals that may be very s i m i l a r (analogs) to safe chemicals are known to be dangerous. In f a c t , analogs of metabolites can be among the most dangerous chemicals. Therefore, each new chemical should be tested f o r safety no matter what i t s structure i s . However, microorganisms known to be safe have been mutated and have exchanged genes i n laboratories and there has been no case of a man-made derivative of a safe organism becoming a s i g n i f i c a n t problem. Thus, analogies of recombinant microorganisms with chemicals i s not always appropriate when considering safety concerns. Current technology with chemicals has caused genetic changes i n microorganisms that have been detrimental. For example, herbicides applied to the s o i l provide a source of food f o r microorganisms that mutate to e f f i c i e n t l y degrade the chemical and thus render i t i n e f f e c t i v e against weeds. Use of a n t i b i o t i c s has enriched the environment f o r antibiotic-degrading bacteria. Problems caused by these genetically altered microorganisms can readily be solved by discontinuing use of the chemicals. Many researchers hope that recombinant DNA technology w i l l develop medical and environmental products to replace some of these chemicals and, therefore, to a l l e v i a t e problems that such chemicals currently cause.
NATURAL SELECTION A plant or microbe contains thousands of active genes. Every minute, phenomenal numbers of organisms undergo the natural process of mutation and exchange of genes. Organisms are continually being transported across ecosystems to new environments, and evolution slowly progresses as a rare organism increases i t s a b i l i t y to survive and multiply. There i s more and more evidence that genes have naturally crossed genus and even kingdom b a r r i e r s . Adding manmade strains to our environment should have neglible impact compared to normal processes. The number of genetic alterations through s c i e n t i f i c experiments are of much smaller magnitude than alterations occurring d a i l y i n nature. As new selective pressures appear, an organism i s either able to compete or i s selected against. In cases when man adds a new chemical to the environment, the mere presence of that chemical can give an organism an " a r t i f i c i a l " s e l e c t i v e advantage. Examples include a n t i b i o t i c and herbicide metabolism noted above. In the absence of such " a r t i f i c i a l " s e l e c t i o n (e.g. by a s p e c i f i c chemical), an organism survives because i t i s adapted to handle many varied selective pressures. Thus, a great many s p e c i f i c genes are
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required by an organism to remain competitive i n changing environments over a s i g n i f i c a n t period of time. Scientists have demonstrated that even a single gene not needed by a bacterium can give that bacterium a s e l e c t i v e disadvantage. Over time, genes not helping a bacterium survive i n the environment most l i k e l y w i l l be lost through mutation. Those organisms which maintain a non-functional gene w i l l be at a selective disadvantage r e l a t i v e to those that have l o s t the non-functional gene through mutation. Plants developed f o r increased y i e l d through intensive a g r i c u l t u r a l practices are extremely d e b i l i t a t e d i n t h e i r a b i l i t y to compete i n the wild. Adding disease resistance properties or increased seed production through mutation and breeding have not given the crop an opportunity to become more adaptable. Each modification f o r man's use further d e b i l i t a t e s an organism's a b i l i t y to compete i n nature. The eons of s e l e c t i o n , mutation and recombination have given us organisms that are e f f i c i e n t l y adapted. A s c i e n t i s t would have an extremely d i f f i c u l t time purposely engineering an organism to be better adapted to a natural environment. There i s no basis f o r the b e l i e f that a plant or microorganism derived through genetic engineering w i l l unintentionally become more competitive and create an environmental problem.
CONTAINED TESTS TO DEMONSTRATE SAFETY In order to demonstrate unexpected problems from released genetically engineered (or any other genetic alteration) organisms, small-scale f i e l d tests are e s s e n t i a l . Suitable laboratory tests to demonstrate that no unpredicted f i e l d problems w i l l emerge with recombinant organisms are unlikely to be devised i n the forseeable future. No greenhouse or laboratory tests are required (or have been necessary) to demonstrate safety of mutated or cross-bred organisms released f o r a g r i c u l t u r a l benefit. The researcher c e r t a i n l y i s naturally interested i n the outcome of any experiment, and experimental f i e l d s are routinely monitored f o r both benefits and problems. There should be much greater concern f o r untoward problems from organisms imported to the U.S., than f o r indigenous organisms with several new genes added to them. The major concerns about released recombinant microorganisms seem to be the chance of developing a new disease organism or creating a new organism that w i l l disrupt the environment. If there i s no s c i e n t i f i c basis to predict the kind of disease or even the host of the disease, then i t w i l l be impossible to develop relevant laboratory tests to demonstrate disease-forming properties of the genetically engineered microorganism. Environmental disruption (e.g. water eutrophication) i s not caused primarily by contamination with microbes since every environment i s p o t e n t i a l l y exposed to each type of microorganism. Microbes readily t r a v e l long distances. Problems occur when there i s new selective pressure on an environment. For example, f e r t i l i z e r runoff into our lakes selects f o r populations of microorganisms that would not dominate without
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the runoff. Therefore, i t seems to be an impossible task to demonstrate, by laboratory t e s t s , that a recombinant microorganism (or any other altered microorganism) w i l l disrupt the environment i f one i s unable to predict, and duplicate i n the laboratory, the s e l e c t i v e pressures that a recombinant c e l l w i l l encounter. The fact that a recombinant microorganism may survive i n the s o i l f o r many years and may exchange i t s foreign DNA with other microorganisms should not be a concern. Bacteria considered harmless exchange genes naturally and frequently with pathogens; however, these safe species do not appear as pathogens. If there i s s e l e c t i v e pressure f o r increased growth of a dangerous microbe, then even a single c e l l can do i t s "damage." If there i s no s e l e c t i v e pressure to allow the recombinant microorganism to maintain high populations, then t r i l l i o n s of c e l l s added to the environment would not cause a s i g n i f i c a n t problem. No laboratory test can give adequate confidence that a single c e l l w i l l not remain a f t e r a specified time i n an acre of f i e l d . Thus, i f there i s r e a l i s t i c concern of danger from a release experiment (whether or not the microorganism i s engineered), laboratory data on survival or gene exchange cannot s i g n i f i c a n t l y a l l e v i a t e this concern. Genetically engineered microorganisms, considered through arguments discussed above, w i l l not indicate r e a l i s t i c concerns.
PUBLIC CONCERN Over a decade ago, when genetic engineering experiments began, the s c i e n t i f i c and n o n - s c i e n t i f i c public raised many concerns. These concerns were addressed i n public discussions and debate and ultimately the concerns subsided. Almost a l l recombinant experiments are now performed with minimum containment which c e r t a i n l y causes the researchers involved to come i n contact with genetically engineered organisms. Even though hundreds of laboratories around the world are a c t i v e l y engaged i n these experiments, not a single disease or environmental problem has resulted from this work. Now that s c i e n t i s t s want to purposely add recombinant organisms to the environment to benefit agriculture, we see another series of concerns. These need to be discussed, put i n t o perspective, and regulated on the basis of relevant experience. I t i s important that imagined scenarios do not unnecessarily p r e c i p i t a t e fear and over-regulation of this technology. Genetic engineering has tremendous potential to increase quality of l i f e and to displace practices that now have undesirable consequences. R E C E I V E D July 31, 1986
