The Institute of Food Technologists convened three panels of experts, consisting of IFT members and other prominent biotechnology authorities, to prepare a comprehensive scientific review of biotechnology. The report consists of four sections. The first section—Introduction—appeared in the August 2000 issue of Food Technology; the next two sections—Safety and Labeling—appeared in the September issue; and the fourth—Benefits and Concerns—appears in this issue.One of the difficulties in discussing the benefits and concerns that attend any technology is consideration of the rapid and extensive advances. As a result, most of us, as consumers, are aware in detail of only those technologies with which we, as individuals, are involved. If we are keenly interested in computers, for example, we usually have considerable knowledge of the underlying technology. If we have never touched a computer, we are likely to be unfamiliar with their function. That is no less true of the technologies that support our food supply.
A few generations ago, most of our population lived on farms or in small towns. Nearly all of our food was grown at home, or nearby, and processed by our families or by people we knew. We had confidence owing to personal contact. The technologies were simple and available to all.
The remainder of that picture, however, was not so comfortable. Frozen foods, iodized salt, vitamins, enriched bread, and air transport of fresh foods were unknown. For all except the very wealthy, fresh fruits and vegetables were limited to what was seasonably available. Goiter, rickets, beri-beri, and pellagra were common.
Today, nutrient deficiency diseases in the Western world are a distant memory. A huge variety of food is available year round. For this to be possible, many of these foods are grown thousands of miles away from where we live, and processed by people we neither see nor know. Furthermore, in the United States, expenditures for food are among the lowest in the world—about 10% of average family income. Supporting those facts is an enormous breadth of science and technology, some of which we discuss in this report. That technology is no longer simple and familiar to all. It is complex, and to most consumers, unknown. Discussing the benefits and concerns that biotechnology creates requires discussing these usually unfamiliar technologies into which biotechnology fits.
History teaches another aspect that must be addressed in the course of introducing any new technology. Except for some life-saving medical advances, and sometimes not even then, it is rare for a new technology to receive a broad and enthusiastic welcome. Canned food, for its first hundred years, was viewed apprehensively, and not without reason. In those pre-bacteriology days, it was far more an uncertain art than a solid science. Pasteurized milk, a life-saving technology in its elimination of the microorganisms causing tuberculosis and undulant fever, was originally viewed with deep suspicion. Artificial insemination of farm animals—critical in selective breeding of improved livestock—was regarded as tampering with nature. Margarine was opposed, partly for alleged health concerns, but mostly because it was a threat to the dairy industry. All sorts of health threats—far beyond pacemaker interference—were originally attributed to microwave cooking. Such apprehensions were by no means confined to food, for which we have always understandably felt a close personal concern.
These examples, a few among thousands, illustrate the mix of motives—some rational, some not, some economic, some religious or ethical, some based only on lack of understanding—that have characteristically attended the implementation of innovation. Biotechnology is no exception. We hope that this report will be a useful contribution to civil and rational dialogue which alone can deal effectively with both scientific issues and consumer concerns.
There are numerous specific benefits of recombinant DNA biotechnology-derived foods.
With the use of rDNA biotechnology, there is the potential for enhancing plant availability and growth, and the ability to grow more and better food with increased nutritional value, including improved animal feed. rDNA biotechnology is expected to revolutionize food bioprocessing through improvements in the responsible microorganisms (e.g., bacteria, yeasts, and molds) and efficient production of specialized enzymes and ingredients via fermentation technology. rDNA biotechnology also creates the opportunity to produce edible vaccines and therapeutics for preventing and treating diseases. The use of rDNA biotechnology also has specific environmental benefits, with the development of new varieties of crops that exhibit increased resistance to pests, tolerance to more environmentally benign herbicides, and virus resistance. These and other specific benefits will be discussed in greater detail below.
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Plant Attribute Benefits
In the harsh world of nature, surviving plants (and animals) have evolved to resist environmental stresses and both pest and pathogen attack. The survival of crop plants (and livestock) has been enhanced by human selection and intervention to produce food. In little more than a century, starting with hybridization, which was commercialized in the first decade of the 20th century, scientific breakthroughs enabled new types of plants, such as triticale and seedless watermelons and grapes, to be produced. Starting in the mid-1970s, genetic modification or “engineering” by molecular means became feasible.
A healthy plant produces a variety of compounds to protect itself from being eaten or destroyed (Ames et al., 1990a, b). At the levels commonly consumed in food, few of these naturally occurring compounds are deleterious to human health. However, many of these substances are hazardous if sufficient quantities of the plant are consumed under certain circumstances. Examples include glycoalkaloids in potatoes, cyanogenic glycosides in cassava, trypsin inhibitors in lima beans, and allergenic proteins in a variety of foods.
Plant breeding often has been successful in producing plants with increased pest and disease resistance, while retaining high yields and both taste and processing attributes. Synthetic pesticides are frequently used to produce high-quality and economically viable crops, such as apples and squash. Food crops can be devastated by both above-and below ground microorganisms. While some compounds are available for combating fungi, such as the copper sprays and sulfur used by organic farmers and fungicides used by farmers and home gardeners, these are high-cost and broad-spectrum, often killing beneficial organisms as well. Except for plant breeding and use of insecticides for killing insects that transmit disease, no remedies for combating plant viruses are known (Dempsey et al., 1998). Unlike combating human bacterial infections, very limited remedies are available for preventing bacterial diseases of plants (Lucas, 1998). Antibiotics are available, but their use is not economical.
The susceptibility of a plant to biotic and environmental stresses—such as temperature extremes, chemical challenge and heavy metal exposure (e.g., selenium), and salinity and drought—are affected by the plant’s genetic composition and structure. For example, some leaves have evolved to conserve moisture or resist heat or freezing. Breeders have changed leaf and stem architecture to capture more sunlight and allow for greater air flow through the leaf canopy.
All plants with genes for resistance to pests and disease are evaluated by breeders and processors during initial stages, and are either subsequently commercialized as generally recognized as safe (GRAS), or, if changed by molecular means, reviewed by federal agencies before commercialization (discussed in detail in the Safety section). Numerous scientific associations have become valued participants in the development and regulatory processes for these crops and food products. As examples, AOAC International and the American Association of Cereal Chemists (AACC) ensure that the current state of knowledge is applied through appropriate and standardized analytical testing procedures to ensure the safety and quality of food ingredients and resultant processed foods. Further, AACC has led the advancement in functional criteria for cereal grains such as the baking quality of wheat, relationships of the protein content of corn to product attributes, and other properties important or essential to various food products. This process may take up to l5 years from initial seed selection. Yield is very critical, as are processing properties, quality, composition, and organoleptic properties.
rDNA biotechnology offers the potential for enhancing plant availability and survival, as well as growth. For example, a severe strain of papaya ringspot virus in Hawaii threatened to kill the trees and decimate the livelihood of growers. Little resistance was available for breeding potential. Hence, the viral coat protein gene was transformed into stock, allowing the trees to grow. In 2005, methyl bromide, a soil fumigant widely used in certain areas, must be taken off the market, as a result of international treaty. At present, there is no alternative for controlling soilborne fungal pathogens in strawberry varieties grown in those regions; rDNA biotechnology offers the potential to retain the availability, at reasonable cost, of strawberries. Apple and pear production is constrained by the bacterial disease called fireblight, first described in the 1870s. No satisfactory antibacterial compounds or adequate resistance to the disease is available in apples desired by consumers. rDNA biotechnology research has produced the first trees to resist this devastating disease. Grape vines, which require multiple years to grow and mature before production of both wine and table grapes, are subject to fungi, insects, root disease, and pest problems, which are increasingly difficult to control. Both the quality and availability of wine and whole grapes can be affected. rDNA biotechnology again offers the potential for minimizing damage caused by these agents.
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The advantages of rDNA biotechnology-derived food crops—increased yield and better resistance to pests, disease, and environmental stress—are clearly apparent to growers but not to most consumers. Widespread acceptance of rDNA biotechnology-derived crops will not occur until consumers become convinced of their advantages. So, what advantages are consumers likely to derive from such crops? Here are a few:
• Food-deficient regions of the world may become less common. rDNA biotechnology-derived crops can be developed to prosper under conditions that previously limited or prevented plant growth. This approach will increase world crop production and also increase the variety of crops suitable for growth in any given area. It is unlikely that an abundance of crops of this type will ever become available in a reasonable time frame through conventional breeding practices. Increases in the food supply that are potentially achievable by rDNA biotechnology are likely to greatly exceed those accomplished during the Green Revolution, which relied on conventional breeding practices.
• Improvements in the organoleptic and nutritional quality of foods derived from plants will occur more rapidly and be more pronounced through rDNA biotechnology modification than by conventional breeding.
• Improvements in the shelf life of fresh fruits and vegetables that either cannot be obtained through conventional breeding or are obtained only at a much slower rate will be attainable through rDNA biotechnology modification.
• Reduction in crops of the types and concentrations of allergens, naturally occurring toxicants, and other undesirable constituents will be more easily achieved by rDNA biotechnology modification than by conventional breeding.
• Introduction into crops of disease resisting and health-promoting constituents (e.g., substances that protect against cancer, lower cholesterol, lower blood pressure, ease menstrual and arthritic pain, help maintain bone density, resist infection, and reduce anxiety) which would be exceedingly difficult, slow, or more likely impossible by conventional breeding will be possible by rDNA biotechnology modification.
More and Better Food
Recently, the human population of the globe passed 6 billion, and forecasts predict that this number will grow to 9 billion by 2050 (UN, 1999). While these numbers are more modest than the prediction only five years ago that the population would double by 2030, demographers predict that the vast majority of the growth will occur in Asia, Southeast Asia, and Africa, areas already under significant strain for food production. Even though improved agricultural practices and higher-yielding crops will likely meet the minimum number of calories to sustain human life globally, there is real and significant concern that the needs for adequate nutrition will not be met.
For example, although India produces sufficient food to prevent starvation, more than 30% of its population is malnourished. The situation is even more pressing in Africa, where diseases such as AIDS have reduced the numbers of farming women and children. Furthermore, periodic famines in arid regions in Africa continue to drive increasing numbers of people to malnutrition and starvation. Recent studies have shown that an infant born of a malnourished mother carries the effects of malnutrition into the fourth generation beyond the mother (Galler et al., 1996).
The challenge is not simply to provide a steady supply of food, but a nutritious and safe food supply that improves the health and productivity of the global population. The past 10 years have seen the development of rDNA biotechnology that can play an important, but certainly not the sole, role in increasing the supply and quality of foods for people in the developing economies.
Despite the modest “farm surpluses” currently being produced in some areas (e.g., North America, Australia), the world does not yet grow nearly enough food to meet the demands of the 21st century. Even with human population stability expected by 2050, the world will need farm outputs that are 2.5–3 times greater than current harvests to provide high-quality diets to the world population just five decades from now (McCalla, 1995). Technologies such as hybrid seeds, irrigation, nitrogen fertilizer, and integrated pest management are already in broad use on the world’s best farmlands. Extending the known non-rDNA biotechnology farming systems to the world’s low-yield farming sectors might not even double current world farm output (Waggoner, 1994). rDNA biotechnology is the most important unused technology available to meet this last, huge surge in global farm demand.
Seven academies of science from around the world, including five from developing nations, issued a white paper (NAS, 2000) spelling out the promise of agricultural biotechnology to alleviate hunger and poverty in the Third World. The academies reported that it is essential that we improve food production and distribution to feed and free from hunger a growing world population, while reducing environmental impacts and providing productive employment in low-income areas. This will require a proper and responsible utilization of scientific discoveries and new technologies. The developers and overseers of rDNA biotechnology applied to plants and microorganisms should make sure that their efforts address such needs. The academies stated that foods can be produced through the use of rDNA biotechnology that are more nutritious, stable in storage, and in principle health promoting—bringing benefits to consumers in both industrialized and developing nations.
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Any shortfall in the effort to triple current yields on the world’s existing farmlands over the next 50 years is likely to mean massive malnutrition for the world’s poorest people. It is also likely to mean the plowdown of millions of square miles of forests and wildlands and thus the probable sacrifice of millions of irreplaceable wild species (Avery, 1997).
Organic farming is often held up as the agricultural ideal for the 21st century. Unfortunately, the U.S. has only about one-third of the organic nitrogen needed to support current U.S. farm output (Van Dyne and Gilbertson, 1987). Countries such as India and China have even less of the organic nitrogen that would be needed; they already feed much of their biomass to livestock and burn animal feces for cooking. The world as a whole may have only one-fourth of the organic nitrogen necessary to support its current food production, let alone triple for 2050.
In addition to sheer caloric needs, hundreds of millions of the world’s poor people are still short of the protein and micronutrients needed to ensure long and healthy lives. rDNA biotechnology has already demonstrated, through such successes as chymosin, “golden rice,” and acid-tolerant crops, that it is one of the most promising ways to meet these urgent needs.
“Golden rice” has been genetically modified through rDNA biotechnology to have increased beta-carotene content, which may help to overcome the severe vitamin A deficiencies which cause millions of poor children to go blind or die every year in low-income, rice-consuming cultures. A related product of rDNA biotechnology may also help eliminate the iron deficiency which threatens hundreds of millions of rice-culture women and their babies with birth complications each year (Gura, 1999). Toxic metals, such as aluminum and manganese, are widely present in “acidic” tropical soils, which account for nearly half the arable land in the tropics. These metals reduce root growth, cutting yields by up to 80%. To produce acid-tolerant crops, two researchers in Mexico inserted a gene from a bacterium into tobacco and papaya. The plants thus secrete citric acid from their roots, chelating these toxic metals (De la Fuente et al., 1997). The yield gains now anticipated from making such soils accessible will be critical to protecting the tropical forests, which contain most of the world’s species of plants and animals. These examples are discussed in greater detail below.
rDNA biotechnology should also be able to play key roles in protecting, preserving, and processing foods, to minimize food losses, maintain or improve quality, and increase processing efficiency. The result should be better health, greater food enjoyment, and still less competition between people and wildlife for scarce land.
If the need for improved farming and food technologies is viewed in purely economic terms, the 21st century will see a huge increase in the demand for farm exports. The rapidly rising affluence and demonstrated protein hunger in such densely populated countries as China, India, and Indonesia virtually guarantee that the temperate-zone countries well endowed with farmland (such as the U.S., Canada, Argentina, France, and Germany) will have the opportunity to help meet the soaring food demand in the emerging economies. Agriculture in the developed countries thus could make a major environmental contribution while increasing production each year for additional farm exports. Hundreds of thousands of additional urban jobs would also be created by such an expansion of farm exports, in food processing, transportation, and many associated fields.
Food Technology and Bioprocessing Benefits
Production of various foods and food ingredients through fermentation, also called bioprocessing, has occurred since the earliest records of man’s preservation of foods. Microorganisms and enzymes are used widely for the conversion of raw food substrates (e.g., milk, cereals, vegetables, and meats) into a plethora of fermented products (e.g., cheeses, cultured milks, sourdough bread, pickles, wine, beer, and sausages). Bioprocessing technology has been further developed for specialized production of food ingredients (e.g., organic acids, amino acids, vitamins, and gums), or processing aids (enzymes). rDNA biotechnology is expected to revolutionize food bioprocessing across all of these arenas through improvements in the responsible microorganisms (e.g., bacteria, yeasts, and molds) and efficient production of specialized enzymes and ingredients via fermentation technology.
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Ingredients made by bioprocessing are among some of the most attractive products of rDNA biotechnology. An understanding of metabolism and the ability to redirect metabolic pathways provide opportunities to produce food ingredients of higher quality and purity, as well as new ingredients for purification or synthesis that are not available through conventional methods. As discussed below, key ingredients targeted by rDNA biotechnology include organic acids, bacteriocin preservatives, enzymes, and microorganisms used for processing aids. rDNA biotechnology is also important in the production of vitamins and amino acids.
• Organic Acids. Organic acids are commonly used as food acidulants and are among the most versatile food and beverage ingredients because of their solubility, hygroscopic, buffering, and chelation properties (Moresi and Parente, 1999). Lactic, citric, gluconic, and propionic acids are all naturally occurring and produced by fermentation. Citric acid has the widest range of applications and with acetic acid accounts for 75% of food acidulant usage. Citric acid is produced by several molds, yeasts, and bacteria by fermentation of glucose via glycolysis. Mutants of fermentation strains have been selected with steps in the Krebs cycle blocked to maximize accumulation of citric acid. Improvements via rDNA biotechnology have increased the rate of glucose fermentation and eliminated enzymes that degrade citrate in the production organisms.
Lactic acid is used as an acidulant for cheeses, meats, jellies, and beer. Derivatives of ammonium lactate are used as sources of non-protein nitrogen in animal feeds, and sodium or calcium stearoyl lactylates are used as emulsifiers and dough conditioners. Fermentation processes produce both the D and L isomers of lactate via the two stereospecific lactic dehydrogenases—L-LDH and DLDH. L-lactate is the natural and preferred form for food use because it is the form used by humans and the D-form is considered slightly toxic. Two key improvements have occurred via rDNA biotechnology. First, elimination of D-LDH by gene replacement leads to pure L-lactate production in Lactobacillus species (Bhowmik and Steele, 1994; Lapierre et al., 1999). Second, the bovine L-LDH gene was introduced into Kluyveromyces lactis, leading to significant yield increases in L-lactate (Porro et al., 1999).
Lactic acid bacteria show considerable promise for metabolic engineering because their biosynthetic pathways are completely separate from their energy generating pathways. As a result, either pathway can be manipulated without affecting the other. In a landmark example, the homolactic pathway of Lactococcus lactis was redirected to a homoalanine fermentation (Hols et al., 1999). Stereospecific production (>99%) of the preferred form, L-alanine, was achieved, using metabolic engineering to produce a product (alanine) that is not a normal product of the organism’s metabolism. Industrial production of this stereoisomer in food products or bioreactors is now possible.
• Bacteriocin Preservatives. Bacteriocins are peptide antimicrobials that kill bacteria. Nisin is notable among these because of its broad killing range against Gram-positive pathogens and its GRAS status based on its safe consumption in dairy products for centuries. Genetic approaches to understanding the regulation of nisin biosynthesis in Lactococcus have identified the fermentation conditions where nisin, or other enzymes/proteins, can be overproduced, approaching 50% of the cells’ protein (Kleerebezem et al., 1997). The increased availability of nisin has led to expanded applications for this preservative in foods. Moreover, expression systems using the nisin-inducible promoter are already providing powerful tools for production of food-grade enzymes and protein ingredients by L. lactis.
• Enzymes. Enzymes were important agents in food production (e.g., milk clotting, bread production, juice clarification, alcoholic beverage production) long before modern rDNA biotechnology was developed. Today, enzymes are indispensable to modern food processing technology. The U.S. market for enzymes used in food manufacture is expected to grow to $214 million by 2006 (Roller and Goodenough, 1999). An increasing variety of food enzymes has been produced using rDNA biotechnology. Their accepted use in foods is based on the following facts: enzymes produced by rDNA biotechnology are identical to their natural counterparts (e.g., chymosin); enzyme preparations are free of any deleterious substances that could be introduced during the bioprocessing and purification steps (e.g., endotoxins from Escherichia coli); and viable rDNA biotechnology-derived microorganisms are not present in the final preparation.
The first example of a processing enzyme produced by rDNA biotechnology for use in food was chymosin (reviewed by Roller and Goodenough, 1999). Chymosin is the most important enzyme used in the dairy industry to clot milk. Its specific hydrolysis of kappa-casein destabilizes milk micelles and leads to rapid coagulation, clean flavor, and maximum protein yields from cheese curds. Traditionally, chymosin was obtained from rennet extracted from the stomachs of young calves. Rennet supplies faced major declines as calf slaughter decreased during a period of increasing worldwide cheese production. Several commercial entities undertook efforts to clone and express chymosin, in its exact natural form, from bacteria (E. coli), yeast (K. lactis), and molds (Aspergillus niger var. awamori). Chymosin that was produced in bioreactors was identical to the animal-derived enzyme and was substantially purer (>95% chymosin) than traditional rennet (containing only 2% chymosin).
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Since these were the first products of rDNA biotechnology targeted for use in human foods, extraordinary precautions were taken to assure that the enzyme preparations were free of toxins, had no live recombinant organisms, and exhibited no ill effects in animal studies. Indeed, although E. coli is not a foodgrade organism, the Food and Drug Administration concluded that chymosin produced from recombinant E. coli was identical to its conventional counterpart and, therefore, could be considered to be a GRAS substance acceptable for use in foods (FDA, 1990). Estimates of the use of rDNA biotechnology-derived chymosin now exceed 80% of the market in the U.S. and Canada, where cheese produced using rDNA biotechnology-derived chymosin is regarded as vegetarian, kosher, and halal.
The chymosin example established the basis for production of a variety of safe and functional rDNA biotechnology-derived food-grade enzymes. Improvements are readily apparent in enzyme availability, purity, and cost, which benefit and improve the quality of foods available to consumers. Commercial and near-market rDNA biotechnology-derived food enzymes are listed in Table 1.
Because of the considerable benefits to be realized, it is probable that most food processing enzymes eventually will be rDNA biotechnology-derived. Enzymes of higher purity and specificity can be obtained, which will improve processing efficiencies and quality, while reducing energy costs, waste, and environmental impacts.
• Processing Aids—Microorganisms. Many beneficial microorganisms are directly responsible for the preservation and processing of food, including primarily yeasts (Saccharomyces cerevisiae), beneficial molds, and lactic acid bacteria. rDNA biotechnology offers considerable promise for the beneficial modification of microorganisms that drive food fermentations. Examples of microorganisms modified through rDNA biotechnology for bioprocessing that are currently approved for food use are listed in Table 2.
In those examples where rDNA biotechnology modifications were made in yeast, self-cloning was used. This concept is based on the fact that DNA rearrangements occur naturally and often within the genome of any given organism. Self-cloning protocols require that only DNA originating in the host organism can be manipulated and reintroduced to create an improved microorganism.
For bioprocessing microorganisms, there remain many attractive targets for improvement through rDNA biotechnology. Most of these offer improved product quality, better control of fermentations, and thus enhanced food safety. It is pertinent to note that progress in molecular biology and genomics has provided both the tools and targets for precise genetic modification of microorganisms. Specific genes and DNA sequences can be introduced, eliminated, or altered in a precise manner in microorganisms in many cases. If desirable, marker genes and extraneous DNA can be removed. These specific changes are superior to nondiscriminating strategies that have been used historically to mutagenize DNA, in chance efforts to select more-efficient organisms. History claims many successes in the selection of improved organisms (e.g., 10,000-fold increase in penicillin production from Alexander Fleming’s original Penicillium strain). However, the mutations are random and nondiscriminating, and any effects of secondary mutations are not known. In contrast, rDNA biotechnology has provided the tools and information to make more-specific genetic changes, ensuring both performance and safety.
• Animal Feed. Over the past century, a remarkable revolution in both animal and plant agriculture has led to a relatively stable and cheap supply of food for the developed world. In parallel with the Green Revolution, there has emerged an equally important revolution in animal feed efficiency. This was essential to provide for the developed world’s demands for high protein content of their diets. For example, 56% of the protein in the developed world’s diets comes from animal products, compared with only 11–26% in the developing countries (Delgado et al., 1998). In the U.S. at the turn of the century, it took about 6 pounds of feed to produce a single pound of weight gain in a chicken. Today, only 1.5 pounds of feed are required (Gordon, 1996; Williams, 1997). Similar improvements have been seen in hog production. However, this revolution in animal genetics has led to a significant increase in animal nutritional requirements, which are poorly met by current crop plants. In essence, animal nutritional needs now exceed that which can be provided by the basic commodity plants on which animals rely for calories (Olsen and Frey, 1987).
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This divergence between plant supply and animal demand has occurred because selection for improved plant productivity has focused primarily on plant yield per acre of land and has largely ignored the nutritional needs of the animal. In parallel with this, improvements in animal genetics have focused primarily on increased efficiency of feed conversion, assuming a near optimal feed composition. Thus, plant and animal breeders have been inadvertently widening the gap between the increasing nutritional needs of the animal and the ability of the crops used for feed to meet those nutritional needs.
To optimize animal nutrition, the animal feed industry has flourished during the last century. The growth in the feed supplements business was critical to meet the demand for macro- and micronutrients as feed additives. By monitoring essential feed components, least-cost feed formulations have evolved. Coupled with a vertically integrated system from farm to consumer, this has resulted in a supply of high-quality meat at affordable prices in the developed world. The basic commodity-feed components of calories and protein supplied by the crop plants are the base of the supply chain. Today, a significant proportion of world crop production is directed into animal feed in the form of forage, silage, or grain (Bradford, 1999). For example, 80% of U.S. maize production is used for feed for poultry, hogs, and cattle (USDA/ERS, 2000a). Although the developed world’s meat consumption is projected to be stable, world meat consumption is expected to rise very significantly during this century because of increased demand for animal products in the developing world (Delgado et al., 1998).
By examining today’s animal feed conversion ratios, it becomes clear that the greatest efficiencies in animal productivity are primarily based on chickens and hogs. For every pound of weight gained by a chicken, approximately 1.5 pounds of feed is required. For hogs, the feed requirement is approximately 4 pounds for every pound gained, whereas for beef cattle the feed requirement is more than 10 pounds. These conversion ratios demonstrate the importance of a high density of essential nutrients as well as calories. The shortfall in calories and essential amino acids available from cereal feed is partially offset by mixing corn with soybean to make a mixed soybean/corn feed. To improve the caloric value further, feed is supplemented with fats such as animal offal and feed-grade animal and vegetable fats which include by-products of the restaurant, soap, and refinery industries. Other nutritional needs are met by adding various feed additives to the mix. Productivity is enhanced by managing an optimal environment for the animals to grow. It is here where significant emphasis is placed on animal health as it relates to carcass quality.
The first major improvement in animal nutrition was the addition of vitamin D, which allowed chickens to be raised in controlled environments. This in turn minimized losses due to environmental changes, predators, and disease. Further improvements came with diets supplemented with vitamin E as an antioxidant, methionine to improve immune function, conjugated linoleic acids to improve feed efficiency and carcass quality, enzymes to improve digestion and remove antinutritional factors and toxins, antibiotics to optimize animal health and stabilize weight gain, prebiotics and probiotics to improve gut microflora, and growth hormones to improve feed efficiency. Today, there are many feed supplements and additives with varying efficacies (Kellems and Church, 1998). Some are macronutrients and others micronutrients, yet others are more veterinary pharmaceutical in nature. Most are aimed at improving carcass quality while maintaining or improving animal feed efficiency. A wide array of methods for producing these feed additives are used across the world, from fermentation to synthetic chemistry, and some already rely on the application of rDNA biotechnology. The key emphasis is placed on quality linked to the cost of production.
As we move forward in the new century, a new revolution is occurring. Through dramatic advances in genetics and rDNA biotechnology, it is now possible to envision ways of enhancing animal feed by directing the plant itself to produce a more nutritious product (Bonneau and Laarveld, 1999). With this advance comes the opportunity to redesign and rethink the basic composition of feeds derived from silage, forage, and grain. This change will go beyond plant yield as a commodity product and enter the realm of value-added crops. In the developing countries, where meat consumption is very much lower than in the developed world, these rDNA biotechnology-driven advances in plant composition for animal feed present another opportunity to improve human nutrition.
Collectively, these genetic improvements in crop composition have been termed the “output traits” to distinguish them from the input traits that were the hallmark of the first wave of rDNA biotechnology-derived products, which included resistance to herbicides, insects, and viral diseases. Thus, a new industry to improve feed crops is emerging as an adjunct to the existing feed supplement industry. The seed genetics industry, linked to rDNA biotechnology, is altering seed and plant traits to improve basic plant components.
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Some output traits already on the market include silage corn improved by the mutant brown-midrib trait, producing so-called BMR-corn (Mazur et al., 1999). This corn has a mutation in the pathway leading to lignin deposition that significantly increases its digestibility for ruminant animals. A more recent improvement in maize was the development of corn with a higher-oil content. In this case, the maize seed was selected to have a significant increase in oil content, from 3.5% in conventional maize to about 6% oil in higher-oil corn. Varieties having the higher oil content have grown significantly in market share over the last few years. A further improvement came with the development of corn with increased protein and essential amino acids necessary for optimal animal growth.
In soybeans, improvements such as altered oligosaccharides to reduce non-digestible components (stachyose, galactose, and raffinose) and increased oleic acid composition have emerged. Increased plant resistance to fungal infections will reduce the risk of serious contamination with mycotoxins (discussed in the food safety improvements section below). In all crops, it seems reasonable to expect additional improvements through further enhancements in oil, fatty acid, protein, starch, carbohydrate, vitamin, antioxidant, and mineral composition.
A new area of animal feed improvement aids control of environmental pollution. In the intensive livestock industry, there are significant problems with odors and controlling the release of unused nutrients, such as nitrogen and phosphorus from animal waste (Dourmad et al., 1999; Poulsen et al., 1999). A significant step forward in resolving the major political and economic issue of phosphorus pollution was the identification of approaches to control phytic acid content of feed by reducing the phytate content of seed via rDNA biotechnology or adding phytase to feed via supplementation. A new development involves reducing the phytate content of the seed significantly by introducing the lpa1-mutant of corn. Low-phytate corn is new on the market. Recent studies have revealed that it has an unexpected nutritional enhancement, namely, an increased bioavailability of amino acids. Phytate also strongly chelates iron, calcium, zinc, and other divalent mineral ions, making them no longer bioavailable. This means less phosphorus waste as well as reductions in nitrogen waste.
Collectively, these genetic enhancements in feed composition have been achieved by introducing valuable traits directly into the commodity component, the plant itself. This is a significant technical challenge for both conventional plant breeding and rDNA biotechnology. Nevertheless, significant progress has already been made through a combination of conventional breeding, germplasm screening linked with high throughput tests of specific traits, rDNA biotechnology-aided breeding using DNA markers, selection for mutants carrying specific traits, and rDNA biotechnology (transgenic) approaches, which involve isolating, characterizing, and modifying individual genes followed by plant transformation and trait analysis. In all of these approaches there is an overriding imperative to maximize plant yield, because the least-costs feed analysis will continue to rule this market sector. Thus, it will be necessary to provide a platform which will continue to be based on delivering products using the cheapest methods available. This is perhaps the most challenging step of all, since yield requires many genes all functioning optimally in the plant. These enhancements are a key next step in securing and improving the world food supply in the new century for both the developed and the developing nations. Furthermore, these enhancements are expected to also alleviate some environmental problems associated with intensive livestock production.
• Plant-Based Animal Vaccines. Animal health benefits appear to be possible, as certain vaccines and growth hormones are amenable to an rDNA bio-technology approach (McKeever and Rege, 1999). At present, animals receive multiple injections to maintain their optimal health and high feed efficiency. This is inconvenient, causes some distress to the animal, and can cause some meat spoilage. By engineering a plant to express some of these products it appears to be possible to circumvent these concerns. Further advances seem highly likely in this type of technology.
Howard (1999) demonstrated production in plants of a vaccine against transmissible gastroenteritis virus which protected swine in clinical trails against the virulent pathogen. Dalsgaard et al. (1997) demonstrated that a cowpea plant-based vaccine protected mink against the diarrhea and anorexia caused by mink enteritis virus (MEV), a member of a group of viruses that is also responsible for disease in cats and dogs. To develop the plant-based vaccine, a segment coding for the epitope (antibody binding site on an antigen/allergen) of MEV was fused into the coat protein gene of a cowpea mosaic virus. Mink immunized by injection with the chimeric virus obtained from the rDNA biotechnology-derived plants resisted subsequent challenge with MEV; most of the unimmunized animals quickly succumbed to the disease.
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Farmers and producers have enthusiastically embraced the new varieties of rDNA biotechnology-derived crops that exhibit increased resistance to pests (e.g., corn, canola, cotton, and potatoes with Bacillus thuringiensis (Bt) genes for insecticidal proteins); tolerance to more environmentally benign herbicides (e.g., corn, cotton, soybeans); and virus resistance (e.g., squash, cucumbers, papaya).
Although a major driving force for adoption of these crops is economic, farmers also welcome the environmental benefits of fewer pesticide residues and simplification of farming practices. In general, farmers who use the new varieties have realized significant savings in production costs, as well as increased yields (USDA/ERS, 2000b). These savings occurred despite the increased costs of seeds and “technology fees” that were added by seed producers to recover expenses for research and development.
A recently released summary of the proceedings of the Ceres Conference on Agricultural Biotechnology (Doyle, 1999) describes the results of independent third-party studies to document farmer acceptance and profitability of rDNA biotechnology-derived crops. For example, 45% of farmers had higher yields of Bt corn compared to conventional corn in 1998, and nearly 26% of farmers growing Bt corn reported a decrease in pesticide use. Studies have demonstrated that farmers can save as much as $27 per acre in overall growing costs with glyphosate-tolerant soybeans. Data indicate that some farmers earned a net profit of about $40 more per acre for rDNA biotechnology-derived cotton compared to the conventional varieties. Data from the Canola Council of Canada for the 1998 season (Doyle, 1999) showed that, compared to conventional canola, glyphosate-tolerant varieties produced greater yields (31 bushels/acre compared to 28.6 bushels/acre) and greater profits ($86 per acre compared to $52 per acre). In addition to economic advantages, the number of pesticide applications is typically reduced. As an example, canola fields require only one herbicide application (instead of two), and glyphosate provides broader-spectrum weed control. Certainly, rDNA biotechnology can play an important role in development of agriculture that uses fewer and more-benign agrochemicals than needed with traditional crop varieties.
Researchers found that glyphosate-tolerant soybeans offered easier weed management, less injury to crops, no restrictions on crop rotations, increase in no-till agriculture, and reduced costs. U.S. farmers using glyphosate-tolerant soybeans saved an estimated $220 million in 1998 due to lower herbicide costs. The broad spectrum of weeds controlled by glyphosate means that soybean growers no longer need to make multiple applications of complex combinations of herbicides.
Before the introduction of tolerance genes from other organisms, herbicides were selected by screening for chemicals that caused minimal crop damage while killing as many common target weeds as possible. Broad-spectrum herbicides like glyphosate were most often used to kill vegetation in places like railroad tracks, paths, and parking lots. Glyphosate inhibits an enzyme essential for the synthesis of aromatic amino acids in plants. Researchers found a form of the enzyme that carries out the same step in a bacterium and which is not inhibited by this herbicide. Glyphosate-tolerant soybeans carry the bacterial gene and are relatively insensitive to the herbicide. Extensive tests by the manufacturer of glyphosate have shown that it has a very low mammalian toxicity and is rapidly degraded in the soil after application (Padgette et al., 1996). Its microbial degradation ultimately produces carbon dioxide and water. No toxic intermediates or derivatives have been identified among its breakdown products (Sanders et al., 1998). Unlike earlier herbicides that persisted in the environment and contaminated ground water, glyphosate appears to be safe and to disappear rapidly.
Similarly, rDNA biotechnology is now being used to develop varieties of soybeans and other crops that are tolerant to other herbicides, which would otherwise kill them. Two other herbicides with different modes of action, glufosinate and imidazolinone, are also being used on crops protected with transgenes. Corn resistant to sulfanyl urea has also been produced by the selection of mutants in tissue culture.
The introduction of herbicide tolerance has contributed to the development of no-till agriculture and crop rotation with benefits that include savings on fossil fuel in preparing seedbeds, and reductions in soil erosion and in air pollution from burning crop residues.
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The most widespread rDNA biotechnology-derived crops in the U.S. at the present time are cultivars of soybean, cotton, and corn. In the U.S. in 1999, 35% of the corn acreage (77.4 million acres) was made up of either insecttolerant (23%) or herbicide-tolerant cultivars; 45% of the cotton acreage (14.8 million acres) was insect-tolerant;and 54% of the soybean acreage (72.9 million acres) was herbicide tolerant. A USDA/ERS (1997) study found that herbicide-tolerant soybeans reduced farm input costs by 3–6% and increased average yields by more than 13–18% in most regions of the U.S. Estimated benefits of herbicide-tolerant corn and canola range from $15 to $24 per acre (James, 1998). Considering that the planted area of rDNA biotechnology-derived crops more than doubled in 1998 to nearly 69 million acres (James, 1998), many farmers have obviously become convinced that rDNA biotechnology-derived varieties have superior characteristics.
Certain segments of the commercial seed markets have already become highly concentrated. Two companies together account for more than 50% of North American sales of corn seed and nearly 40% of North American soybean seed sales (Hayenga, 1998). Based on data contained in their recent annual reports, two other companies account for more than 40% of global commercial sales of fruit and vegetable seed.
Even in the relatively concentrated U.S. hybrid corn seed market, increases in seed costs have been less than half the value of yield increases attributable to new varieties for the period 1975 through 1998 (Artuso, 2000). A recent study of the distribution of benefits resulting from introduction of Bt cotton estimated that the biotechnology firms involved captured 44% of the value of the innovation, with farmers receiving 48% and consumers 8% (Falck-Zepeda et al., 2000). The estimated benefit shares derived in the study were based on data for 1997, which was only the second year in which the Bt variety was available. As competitors develop their own varieties of Bt cotton, the premium that can be charged for this variety can be expected to decline. The effect of competition can already be seen in the market for herbicide-tolerant soybeans. In this more-competitive market, the share of the economic benefits captured by the companies that introduced the first of these varieties is estimated at less than 25% (Falck-Zepeda et al., 2000).
Diet, Nutrition, and Health Benefits
rDNA biotechnology has the potential to improve the nutritional status of populations throughout the world. Both developed and developing societies can benefit from rDNA biotechnology-derived plants that will provide increased quantities of foods, as well as foods with unique and more-effective nutritional composition and qualities that will satisfy the individual needs of different populations.
There are many types of malnutrition, but all can be traced to two major sources, the lack of proper quantity and quality of foods. rDNA biotechnology offers unique opportunities to increase the quantity of food that is available in developing countries. In both developing and developed countries, rDNA biotechnology can also improve the nutritional quality of foods. Specific foods can be developed to correct malnutrition problems that are unique to different regions of the world. As discussed above, plants can be modified to grow well in areas of low production potential. They also can be modified to provide increased and more-stable quantities of essential amino acids, vitamins, or desirable fatty acids. For example, deficiencies of vitamin A and iron are serious, life-threatening health problems in many regions of the developing world. Vitamin A deficiency can increase susceptibility to infections and cause blindness. An inadequate consumption of iron results in anemia. According to the World Health Organization, vitamin A deficiency affects approximately one quarter of a billion children, with child death rates as high as one out of four in some regions of the world. Iron deficiency affects 3.7 billion people (Gura, 1999). rDNA biotechnology-derived golden rice with increased content of beta-carotene, the precursor to vitamin A, is under development, and foods with enhanced iron content are also in the research pipeline.
Other regions of the world suffer malnutrition because their dietary sources of protein are inadequate. Because diets provide an inadequate source of protein, children suffer from stunted growth, increased susceptibility to infections, and impaired intellectual development. Approximately 195 million children worldwide are so affected. Through the use of rDNA biotechnology, the essential amino acids content of cereal grains such as corn and rice can potentially be increased to improve both the protein quality and quantity, thereby eliminating this form of malnutrition (Larkins, 1999). Similar efforts to improve protein content and quality through conventional methods have met with only limited success.
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Research is being conducted to produce plants with altered nutrient composition, such as increased fiber content, to produce oils that have better nutritional quality and stability, and to enhance components that may be useful in reducing the incidence of several cancers and other chronic diseases (USDA/ERS, 1999). As the science of nutrition improves and develops our understanding of the relationships between genetics, diet, and degenerative diseases, recommendations for dietary consumption practices will also change. In addition to classical nutrients, other plant components (i.e., phytochemicals), are now recognized for their contributions to improved health and the prevention of some degenerative diseases. It will also be important to provide foods of appropriate composition to achieve maximum benefits.
Scientists predict that in the near future rDNA biotechnology-derived foods with improved levels of phytochemicals and micronutrients will be developed. Some have predicted that these and other products will be well received by health-conscious consumers, who spend more than $6 billion annually on over-the-counter food supplements.
Probiotics are living microorganisms, typically delivered through foods, that offer benefits to health and wellbeing that are beyond basic nutrition, such as increased resistance to foodborne illness, decreased risk of some cancers, and potential lowering of blood cholesterol (Sanders, 1999). Selected members within the Lactobacillus and Bifidobacterium genera are considered key probiotic species as they are able to survive stomach and intestinal transit, exert health benefits (e.g., stimulation of the mucosal immune system), and favorably affect the microbial ecosystem. rDNA biotechnology and genomics are expected to play an important role in identifying the probiotic strains that are capable of eliciting certain health benefits.
rDNA biotechnology also offers the opportunity to decrease or eliminate the allergenic proteins that occur naturally in specific foods. For example, rDNA bio-technology has already been used to dramatically reduce the levels of the major rice allergen (Matsuda et al., 1993). Similar approaches could be attempted with more commonly allergenic foods such as peanuts.
Plants have been a valuable source of pharmaceuticals for centuries. During the past decade, however, intensive research has focused on expanding this source through rDNA biotechnology. The research brings closer to reality the prospect of commercial production in plants of edible vaccines and therapeutics for preventing and treating animal and human diseases. Possibilities include a wide variety of compounds, ranging from vaccine antigens against hepatitis B and Norwalk viruses (Arntzen, 1997; Dixon and Arntzen, 1997; Mason et al., 1992, 1998) and Pseudomonas aeruginosa and Staphylococcus aureus (Brennan et al., 1999) to vaccines against cancer and diabetes. In addition, genetically modified strains of probiotic microorganisms are also possible vehicles for successful delivery of vaccines and digestive aids (e.g., lactase) through the stomach and the small intestine.
Two seminal papers supported the use of rDNA biotechnology-derived plants for pharmaceutical production (Ma et al., 1995, 1997). These reports were soon followed by one (Ma et al., 1998) describing results of successful human clinical trials with an edible vaccine against a pathogenic strain of E. coli and a monoclonal antibody against cariogenic Streptococcus mutans. Haq et al. (1995) reported the expression in potato plants of a vaccine against E. coli enterotoxin that provided an immune response against the toxin in mice. Human clinical trials suggest that oral vaccination against either of the closely related enterotoxins of Vibrio cholerae and E. coli induces production of antibodies that can neutralize the respective toxins by preventing them from binding to gut cells. Ma et al. (1995, 1998) showed that tobacco plants could express secretory antibodies or “plantibodies” against the cell surface adhesion protein of S. mutans. Used as a bactericidal mouthwash, the antibodies prevented bacterial colonization by the microorganism and development of dental caries for four months.
A similar approach showed that soybean-produced antibodies protected mice against infection by genital herpes (Zeitlin et al., 1998). Compared to antibodies produced in mammalian cell culture, the plantibodies had similar physical properties, remained stable in human reproductive fluids, and exhibited no differences in their affinity for binding and neutralizing herpes simplex virus. Hence, the difference in the glycosylation processes of plants and animals does not appear to effect the immune functions of the plant derived antibodies.
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Non-Hodgkins B-cell lymphoma, the most widespread cancer of the lymph system, is difficult to treat because the B-cell tumors are variable and response to treatment can vary from person to person. Hence, effective therapy requires “personalized medicine” tailored to the genetic makeup of each patient’s tumor. Unfortunately, conventional treatment methods do not meet the needs for rapid production of customized antibodies in sufficient quantities. Monoclonal antibodies used in conventional treatment also tend to be expensive and unreliable, and those produced in bacteria have solubility and conformation problems.
A system using tobacco mosaic virus (TMV) was developed to produce in tobacco plants (Nicotiana benthamiana) a therapeutic vaccine against non-Hodgkin’s B-cell lymphoma in a mouse model (McCormick et al., 1999). Using cells cloned from malignant B-cells of mice, TMV DNA was modified with a tumor-specific sequence from the gene coding for the immunoglobin cell surface marker. Plants were then infected with the modified virus, resulting in expression of cancer-specific antibodies. B-cell proteins were then extracted from the plant leaves for vaccination of the mice. Eighty percent of the mice receiving the plant-derived vaccine survived the lymphoma, while all untreated mice died within three weeks of contracting the disease.
A similar approach was used to develop a vaccine against insulin-dependent diabetes mellitus (IDDM), an auto-immune disease in which insulin-producing cells of the pancreas are destroyed by the cytotoxic T lymphocytes. The “oral tolerance” method of preventing or delaying autoimmune disease symptoms involves the ingestion of large amounts of immunogenic proteins that turn off the autoimmune response. This method of vaccination is gaining recognition as a potential alternative to systemic drug therapy, which is often ineffective. Insulin and pancreatic glutamic acid decarboxylase (GAD), which are linked to the onset of IDDM, are candidates for use as oral vaccines. Blanas et al. (1996) described the development in a mouse model of a potato-based insulin vaccine that is almost 100 times more powerful than the existing vaccine in preventing IDDM. Feeding diabetes-prone mice potatoes engineered to produce immunogenic GAD reduced the incidence of disease and immune response severity.
rDNA biotechnology-derived vaccines are potentially cheap, convenient to distribute, and simple and safe to administer. Production of medically important substances via rDNA biotechnology engineering of plants and microorganisms offers multiple advantages. For plants, production can be done virtually anywhere and has the potential to address problems associated with delivery of vaccines to people in developing countries. Products from these alternative sources do not require a so-called “cold chain” of refrigerated transport and storage, although they will require segregation from conventional foods to prevent inappropriate consumption. Pharmaceuticals or therapeutics produced via genetic engineering of plants also offer an alternative delivery method, feeding versus injection (Howard, 1999), and an alternative to extraction from animal sources. Furthermore, rDNA biotechnology-derived vaccines may also be safer than many conventional vaccines because they consist of pathogen or antibody subunits rather than whole microorganisms. The use of plants can facilitate abundant production of therapeutic proteins without the risk of contamination by animal pathogens, and at substantially reduced cost.
Food Safety Improvements
Preliminary studies have shown the potential for food safety benefits from rDNA biotechnology-derived foods and food ingredients. For example, preliminary studies have shown that Bt corn had levels of fumonisin, a potential cancer-causing agent often found at elevated levels in insect-damaged kernels, that were up to 30- to 40-fold lower than in non-Bt corn varieties (Dowd et al., 1999). Mycotoxins like fumonisin are both a public health issue and an export issue, as European and Asian markets have refused to import U.S. corn because of what they view as unacceptable levels of mycotoxins.
The actual amount of reduction of fumonisin appears to depend on environmental conditions and the specific Bt corn hybrid, but those corn varieties in which the Bt protein is expressed throughout the plant rather than only in specific areas had the lowest fumonisin levels. Bt corn is modified primarily to resist European corn borers, but it also showed lower mycotoxin levels when corn earworms were present in growing fields. However, the mycotoxin reduction was not as significant as when the primary insect pest was the European corn borer. This preliminary result may lead to the creation of corn varieties with greater resistance to a variety of insects, leading to greater protection from mycotoxins.
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Evaluation of Concerns
Changes to our foods have always produced public concerns. This was the case for hybrid corn, margarine, artificial insemination of farm animals, pasteurization of milk, and microwave cooking, and is the case for rDNA biotechnology-derived foods. The transition from traditional plant breeding to rDNA biotechnology-derived crops has raised several issues that need to be addressed. Upon examination, many of these issues turn out to be without merit.
Economic and Access Concerns
• Public Sector Access. Some critics contend that the increasing role of the private sector in research and aggressive patenting of genes and research resources (materials and techniques) is limiting the access to the necessary materials and processes for pioneering research in the public sector. To examine this issue, the National Research Council convened a workshop in 1996 (NRC, 1997), and another in 1999 with the National Academy of Sciences (NRC, 1999). The National Agricultural Biotechnology Council also explored the issue during an annual meeting (NABC, 1995).
A key issue is the scope of patents granted on genes and genetic information as well as on transformation tools and other platform technologies. If concentrated private-sector control of critical genes and technologies becomes a problem, appropriate policy responses include reducing the scope of patents on genes and platform technologies, including obligatory licensing requirements in patent awards, and increasing public-sector funding of basic research to increase the amount of plant genetic information and rDNA biotechnology information in the public domain. One significant industry response to this concern is one firm’s decision to make its extensive rice genome data available to the public for research purposes. In addition, one major biotechnology company recently announced that it will grant patent licenses without charge for the introduction of an rDNA biotechnology-derived crop that will have significant health and nutrition benefits in developing countries (golden rice).
Access to rDNA biotechnology is needed to help meet the need for increasing the world food supply and improving the quality of foods in developing countries (Gilmore, 2000; Pinstrup-Anderson and Pandya-Lorch, 1999). Some believe that a strong public-sector agricultural research effort is necessary to provide the benefits of plant rDNA biotechnology to the world’s poorest people (Conway and Toenniessen, 1999). The agribusiness input industry will need to find ways to donate technology for use in these poor parts of the world where there are few opportunities for commercial returns. There are organizations that seek to facilitate such transfers, such as the U.S. Agency for International Development (USAID). There is also need for increased funding of rDNA biotechnology research at international crop research centers that are part of the Consultative Group on International Agricultural Research (CGIAR) system.
The seven academies of sciences (NAS, 2000) stated that it is imperative that (1) public funding of research is maintained at least at its present level in both CGIAR and national research institutions; (2) governments, international organizations and aid agencies should acknowledge that plant research is a legitimate and important object for public funding and that the results of such research should be placed in the public domain; and (3) innovative and vigorous forms of public/private collaboration are urgently required if the benefits of rDNA biotechnology are to be brought to all the world’s people.
• Agribusiness Consolidation and Competition. As noted above, certain segments of the commercial seed markets have already become highly concentrated. Even in highly concentrated markets, abuses of market power by dominant firms can be restrained by both actual and potential competition. If competing firms can easily enter profitable markets, dominant firms will be prevented from charging exorbitant prices. There are at least four or five large agricultural and life science companies that are aggressively competing for market share in the corn, soybean, oilseed, and vegetable seed markets. In addition to the two dominant firms referred to above, one company has expanded its corn and soybean seed sales in the North American market and has realized strong sales growth for vegetable and horticultural seeds. Yet another company is actively marketing herbicide-tolerant corn and canola seed and has recently established itself as a strong competitor in the vegetable seed market with the acquisition of two smaller companies. In addition, a new joint venture has been formed for development of advanced cottonseed, and another joint venture is competing in the maize, cotton, and oilseed markets.
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To its proponents, continued advances in rDNA biotechnology will be needed to feed a growing world population in an environmentally sustainable manner. For example, the further development and application of rDNA biotechnology to agriculture will lead to improved efficiencies in food production. Strong intellectual property rights are defended as a prerequisite for the private-sector investment needed to realize these potential benefits. Yet some consumer and environmental advocacy groups are concerned that widespread adoption of rDNA biotechnology-derived crop varieties will leave farmers increasingly vulnerable to increases in farm input prices and create unknown risks to the environment and public health. These critics also have concerns about the continuing decline of the small family farmer and the further industrialization of farming.
Critics of rDNA biotechnology contend that the combination of strong patent rights for rDNA biotechnology-derived crop varieties as well as technological constraints on seed reproduction (e.g., sterility genes) could eventually provide major firms with sufficient market power to charge monopoly prices. But the appropriate public-sector response to potential abuses of market power by agricultural biotechnology companies is not to constrain the use of rDNA bio-technology in agriculture, but rather to maintain a vigilant antitrust policy. The potential for restricted competition did, in fact, become an issue in one recent acquisition, where the U.S. Department of Justice (DOJ) required the acquiring firm to enter into binding commitments to license corn germplasm developed by the acquired firm to 150 other seed companies (DOJ, 1998). Antitrust concerns raised by DOJ derailed another planned acquisition (Monsanto, 1999).
To the degree that direct gene transfer may eventually enable crop breeders to incorporate elite traits into even relatively inferior germplasm, advances in rDNA biotechnology breeding techniques could facilitate the entrance of new competitors into profitable seed markets. However, to promote this type of innovative competition, it will be necessary to maintain widespread access both to the technologies necessary for gene transfer as well as to specific genes that code for important agronomic traits. Access to rDNA biotechnology was in fact an issue raised by DOJ in its review of the acquisition discussed above. As a result, the acquiring firm agreed to spin-off its claims to the Agrobacterium method for genetic transformation of corn (DOJ, 1998). As agricultural biotechnology companies continue to increase their investments in genomic research, the requirements for, and scope of, patents granted for genetic information will become an increasingly important policy issue.
From the perspective of economic theory, patent rights should be defined to maximize benefits derived from increased inventive activity net of any costs resulting from monopoly control of new inventions. In 1985, the Board of Appeals and Interferences of the U.S. Patent and Trademark Office (PTO) ruled in Ex parte Hibberd that patents could be issued for inventions relating to any plant, plant seeds, and plant genes (Fuglie et al., 1996). This ruling was followed by a significant and continuing increase in the number of utility patents granted by the PTO for inventions involving plants (Artuso, 2000). A similar relationship can be seen between the approval in 1994 of amendments to the U.S. Plant Variety Protection Act, which strengthened plant breeders’ rights, and the subsequent increase in the number of applications for Plant Variety Protection Certificates (PVPCs) submitted each year to USDA (Artuso, 2000). Although plant utility patents and PVPCs are imperfect measures of innovation in crop breeding, these trends do suggest that there is a close relationship between intellectual property rights and inventive activity by private sector plant breeders. But the benefits and costs of expanded patent rights need to be evaluated from a long-term perspective, taking into account that subsequent inventive activity will be dependent on the scope of intellectual property rights previously awarded. If patents for rDNA biotechnology and genetic information are defined too broadly, this could inhibit future research and development activities.
• Research Incentives. Fruits and vegetables are considered important for a healthy diet. Most rDNA biotechnology-derived crops commercialized and in the pipeline are considered major crops, e.g., cotton, corn, soybeans, wheat, potatoes, rice, canola, sunflowers, peanuts, sugar beets, and sugarcane (Thayer, 1999). Because the development, testing, and commercialization of rDNA biotechnology-derived minor crops (e.g., fruits and vegetables) are often not economically feasible for private-sector firms, the predominant source of rDNA biotechnology-derived minor crops will be the public sector, as it was for virus resistant papaya. There is a need for public research funds, as well as access to genes and tools for research and commercialization of rDNA biotechnology-derived minor plants.
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It is possible that agricultural biotechnology companies will focus on crops and trait improvements that are expected to generate relatively high profits, while ignoring other research opportunities for which societal benefits may be substantial but not easily appropriated (Byerlee, 1996; Pray and Umali-Deininger, 1998). While this potential problem is not unique to rDNA biotechnology-derived crop research, it could become more pronounced as the cost of research, development, and regulatory review of rDNA biotechnology-derived varieties increases. One response to this problem is to reorient public funding for crop breeding to minor crops and crop traits in which there is perceived to be under-investment by the private sector.
An alternative, although not mutually exclusive, policy option is to provide a set of incentives to increase private sector research on crops and traits perceived to have high public benefits. The Orphan Drug Act of 1983 provides a case study of a set of targeted research incentives applied to the pharmaceutical sector. The Act provided tax credits, research grants, regulatory assistance, and seven years of exclusive marketing rights to developers of drugs for diseases that afflict fewer than 200,000 people in the U.S. or otherwise would have limited commercial potential. One study found that the Act has been relatively effective in providing incentives for drug development efforts that would not have occurred without this support (Shulman et al., 1992).
To date, there have been no systematic studies of the costs of developing new crop varieties using rDNA biotechnology. This is a stark contrast to the situation in the pharmaceutical sector, where the cost of developing a new drug is the focus of continual research and policy analysis. Like pharmaceutical product development, crop breeding requires lengthy and repeated trials of potential new products. Regulatory review of rDNA biotechnology-derived crop varieties also requires closely monitored field trials, environmental assessment, and food safety analyses. There remains considerable debate over whether these regulatory processes are excessive or too lenient, but it is difficult to evaluate the merits of alternative regulatory approaches in the absence of information about how these changes might affect the cost and time required to develop new crop varieties. Indeed, improved information regarding both conventional and rDNA biotechnology-derived crop breeding costs would be a substantial benefit to the development of appropriate regulatory, antitrust, and patent policies for rDNA biotechnology.
• General. Environmental concerns have been raised about the impact of pest and disease resistance and herbicide-tolerant plants. All of the new products are carefully tested for safety to mammals and other animal and microbial life. Soil persistence and the likelihood of subsoil water and stream contamination are taken into account by the Environmental Protection Agency (EPA) in deciding whether to register the products for use. Scientists performing these tests and regulators together design testing programs most appropriate for the new products using the most current scientific knowledge and procedures, as it is very important for all agricultural chemicals to be properly regulated and monitored.
• Pest and Disease Resistance. Corn and potato plants have both been successfully transformed with genes from various strains of the soil bacterium B. thuringiensis. These genes encode toxic proteins with specific effects on certain groups of insects. The pollen of Bt plants was reported to be toxic to the larvae of monarch butterflies feeding on the leaves of milkweed plants (Hansen Jesse and Obrycki, 2000; Losey et al., 1999). The Losey et al. (1999) laboratory study was flawed because it did not include a standard dose response, nor quantification of the amount of Bt pollen used. In spite of these serious limitations, almost all print media featured highly critical front-page stories that Bt corn pollen was killing monarch butterfly larvae. The Hansen Jesse and Obrycki (2000) study exposed butterfly larvae to pollen in a laboratory, rather than a field, setting. Other studies, however, have shown that in or close to cornfields the concentration of pollen grains found on milkweed plant leaves is, for the most part, well below the threshold level that has any effect on monarch butterfly larval growth or viability (Sears, 2000).
Field studies at multiple locations—Maryland, Iowa, Nebraska, and Ontario—found that a lethal dose of Bt pollen spreads only a few feet from its source, not the hundreds of feet reported earlier, and there is little overlap between time of corn pollen shedding and monarch larvae feeding on milkweed leaves (ESA, 1999; Nüler, 1999). Furthermore, at the time of approval of Bt crops in 1995 and 1996, EPA required applicants to provide information on effects on non-target organisms and beneficials, e.g., monarchs, lacewings, honey bees, and parasitic wasps. Little effect was noted. EPA considered the effect of Bt crops on non-target organisms, including such insects as monarch butterflies, and concluded that there was no greater effect on them than with insecticide use. EPA’s recent suggestion that farmers locate the required 20% corn refuge areas around the perimeter of the fields, coupled with the limited movement of corn pollen, would virtually eliminate any remaining risk of Bt pollen to monarch butterfly larvae.
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Pimentel and Raven (2000) assessed the overall picture of the effect on the survival of butterfly populations of Bt corn pollen dusting their larval food plants, and concluded that although Bt corn pollen under certain circumstances has the potential to adversely affect the population levels of Monarch butterflies and other nontarget Lepidoptera, these impacts are minimal compared with habitat loss and the widespread use of pesticides throughout the ecosystem. Reporting on experiments on the effect of Bt corn on populations of black swallowtail larvae under field conditions, Wraight et al. (2000) concluded that there was no relationship between mortality and proximity to the field or pollen deposition on host plants. They determined that pollen from these same plants failed to cause mortality in the laboratory at the highest pollen dose tested, a level that far exceeded the highest pollen density observed in the field, and concluded that Bt pollen of the variety tested is unlikely to affect wild populations of black swallowtails.
Studies to examine the breakdown of Bt toxin present in debris from corn and other crops with the Bt transgene indicated that the Bt toxin is rapidly broken down by microbial activity (Sims and Ream, 1997) and that it has no detectable effects on a range of soil organisms that were tested (Sanders et al., 1998). However, Crecchio and Stotzky (1998) suggested that Bt toxin could persist in the soil bound to humic acids and clay, where it may pose a hazard to non-target insects and enhance the selection of toxin-resistant target species. A recent rigorous assessment carried out by EPA, however, concluded that plants registered for environmental release that express Bt toxins derived by rDNA biotechnology do not cause unreasonable adverse effects (EPA, 2000). Since B. thuringiensis is widely used in organic pesticides and is a common soil organism, the exposure of other soil organisms to its toxin is hardly novel.
Resistance to all methods of pest control has been and continues to be a major problem in agriculture. For the first time in the case of rDNA biotechnology-derived products, government, industry, and farmers are trying to manage the use of Bt corn to extend its useful life. Since the widespread use of rDNA biotechnology-derived Bt is likely to shorten its useful life and that of Bt used as an insecticidal spray, refuges that contain non-rDNA biotechnology-derived crop plants to reduce the selection pressure on target insects (Peck et al., 1999) are being employed to delay the accumulation of resistant forms. It is too soon to know how effective this strategy will be. Another approach is to use plant chloroplast-encoded Bt transgenes. The levels of expression of the Bt toxin can be 20,000– to 40,000-fold higher via chloroplast gene expression than nuclear rDNA biotechnology-derived plants (Kota et al., 1999). These high levels are lethal to resistant insect larvae that can grow on sprayed plants but may be so high as to present other hazards in residues from crop debris.
• Transgene Spread by Pollen. There is a concern that the genes for herbicide tolerance may spread via pollen from rDNA biotechnology-derived crops to other native plants. It is theorized that these genes might become established in weed populations, creating forms that would be difficult to control in the future. For soybean, corn, and most other crops in the U.S., this outcome is unlikely because of the absence of related wild species that are either already weeds or have the potential to become weeds.
For those crops that are themselves of weed origin, this problem is a more serious issue. For example, hybrid sugar beet normally takes two years to flower. Its roots are harvested near the end of the first year of growth before flowering. Plants that flower prematurely, or bolt, produce seeds that contaminate the field and give rise to non-hybrid, lower-yielding plants in subsequent crops. In Europe, where bolting is sometimes a problem, a tractor-drawn wick, held above the leaves and soaked with an herbicide, is used to selectively kill the taller-flowering sugar beet plants, which contact the wick. Herbicide-tolerant bolters will reduce the choice of herbicides that can be used in this way. In some rice-growing regions, red rice is a weed in rice paddies. Because it readily hybridizes with cultivated rice, it would be very unwise to use herbicide-tolerant rice in such regions, since the red rice population would rapidly acquire herbicide tolerance, denying rice farmers a tool for controlling it. It is also generally regarded as unwise to produce herbicide-tolerant sorghum for use in the U.S. because of the likelihood of outcrossing to Johnson grass (Arriola and Ellstrand, 1997), which is a particularly difficult weed to control in agriculture.
In Canada, volunteer canola plants that arise from spilled seed from the previous season’s crop can be a problem for subsequent crops of canola and other species. Canola resistant to three commonly used herbicides have arisen in Alberta, Canada, from intercrossing among two adjacent crops that gave rise to doubly resistant volunteers that, in the following year, crossed with a nearby crop tolerant to the third herbicide (MacArthur, 2000). Farmers usually seed a cereal crop after canola and apply a phenoxy herbicide to kill canola volunteers. If the treatment is done properly, the herbicide-resistant volunteers will be eliminated. Although the triply resistant forms can be controlled by other herbicides, such as 2-4 D, their origin points to a failure to manage the release of the original varieties in a way that will safeguard their continued usefulness in agriculture. In short, growing adjacent crops with different transgenes that are better kept apart is not prudent.
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A relatively new technology introduces transgenes, such as those for herbicide tolerance, in the DNA carried by plant chloroplasts (Maliga et al., 1994; Zoubenko et al., 1994). Chloroplasts usually are not carried in pollen grains, so the spread of these transgenes is limited to the seeds produced by the rDNA biotechnology-derived plant. This technology shows promise in restricting the spread of transgenes (Daniell et al., 1998). Chloroplast transformation is technically more difficult to carry out than nuclear transformation, so rDNA biotechnology-derived crops produced in this way are not yet commercially available.
Herbicide tolerance that has spread to weeds is very unlikely to be a problem in the absence of selective pressure from herbicide application and is thus unlikely to be a threat that extends beyond agriculture and cultivation (Duke, 1998).
There is some concern that transfer of genes like Bt to related wild species by out-crossing could increase their competitiveness and lead either to enhanced weediness or to undesirable changes in the wild population. In parts of Mexico, corn and teosinte freely intercross in farmers’ fields. If insect damage exercises significant control of the teosinte population, there could be strong selection for resistance with undesirable consequences for those farmers. However, conventional breeding for insect resistance in corn has not engendered similar concerns.
• Organic Crops. The organic farming community has decided at this time not to use rDNA biotechnology-derived crops. Thus, if an organic crop, grown for its harvested seed, is planted near an rDNA biotechnology-derived crop of the same species, it is likely that some seeds will result from fertilization by pollen carrying a nuclear transgene. With the sensitive DNA detection techniques that are now available, if the transgene signature is detected, it could invalidate the crop’s organic certification. Chloroplast-encoded transgenes will avoid this problem, but so will observing reasonable isolation distances between crops. These isolation distances are used to ensure the genetic purity of named conventional crop varieties grown for seed. The purity of organic crops is addressed in the Labeling section of this report.
• Virus Resistance. The ability to confer viral resistance by using transgenes that incorporate a part of the viral genome, such as a gene encoding the viral coat protein, or a gene responsible for organizing the movement of virus particles from cell to cell through the minute pores (plasmodesmata) that connect them, has had a dramatic impact on several crops. For example, in Hawaii the papaya industry was devastated by ring-spot virus, which has now been successfully controlled by planting rDNA biotechnology-derived papaya with a gene encoding the viral coat protein (Gonsalves, 1998). The viral coat protein gene is used because, above a certain concentration, in or on the plant, the viral coat protein inhibits further growth of the virus. Presumably, this trait evolved so that the virus did not kill its host too promptly.
In the U.S., squash plants resistant to the aphid-borne zucchini yellows virus have been developed and provide effective control (Fuchs et al., 1998). This example has been criticized on the grounds that tests which found that native populations of wild squash relatives (cucurbits) did not harbor the virus and therefore are unlikely to be controlled by it, were on too small a scale. Others have pointed to examples where multipartite viruses may be reassembled by crossing different rDNA biotechnology-derived parents that carry the separate components. It can be theorized that recombination in an rDNA biotechnology-derived host plant between a systemically expressed viral component and the genome of another, randomly infecting virus might result in a new form that could create a serious problem. While conceivable, opportunities of this kind occur all the time when plants become naturally infected with more than one kind of virus.
Recombination between a virally derived transgene and another virus has been suggested as a possible source of a new virus with enhanced virulence. Such recombination has been shown in laboratory studies, especially with high selection pressure (Matthews, 1991). A recent NRC committee concluded that “most virus derived resistance genes are unlikely to present unusual or unmanageable problems that differ from those associated with traditional plant breeding for resistance” (NRC, 2000).
The S35 promoter from cauliflower mosaic virus (CaMV) is used in almost all commercialized rDNA biotechnology-derived crops. A recent, much-publicized article (Hodgson, 2000) suggests that the CaMV35S promoter will cause large-scale genomic rearrangement, with the extreme suggestion that it could cause cancer. Scientists knowledgeable about CaMV35S note that about 10% of the cauliflower and cabbage produced are infected with CaMV, thereby providing 10,000 times greater 35S promoter in the diet than in rDNA biotechnology-derived crops. No evidence of 35S promoter transfer has been observed, in spite of human consumption of CaMV35 in cauliflower and cabbage throughout history.
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• Monoculture and rDNA Biotechnology. Conventional plant breeding and improvements in agronomy have helped farmers to maximize yields and profits (Silvey, 1994). Yield trials of the crop varieties available usually reveal one—or a few that are very similar—that is best for an agricultural region. The dense, uniform crop stands that cover very large areas are an invitation to epidemic pests and diseases that are kept in check by breeding for resistance and by pesticide applications. The Southern corn leaf blight epidemic of 1969–70 revealed the inherent weakness of a crop whose hybrid seed production depended on cytoplasmic male sterility to avoid removing the pollen-bearing tassels (NRC, 1972). The resultant high degree of cytoplasmic uniformity among North American corn hybrids made them acutely susceptible to a strain of a fungal pathogen that devastated about 15% of the corn crop in the U.S. However, the availability of alternative genetic varieties limited this problem to a single year.
A similar level of dependence on a particular transgene could easily arise, as has been shown by the very rapid adoption in the U.S. of herbicide-tolerant soybean and insect-resistant corn. Even though the risk is probably not high, it would be prudent to adopt the same strategy advocated following the Southern corn leaf blight, which was to diversify the germplasm. This is to make sure that there is adequate backup capability that can provide alternative varieties in the event of catastrophic failure. The best way of doing this is still to safeguard germplasm collections and to encourage a broad spectrum of plant breeding activities.
• Food Safety Monitoring. The initial safety evaluation of rDNA biotechnology-derived foods addresses both short-term and long-term potential food safety issues. The issue of longterm human food safety was considered by a recent consultation of the Food and Agriculture Organization of the United Nations (FAO) and the World Health Organization (WHO). The consultation concluded that the possibility of longterm effects being specifically attributable to genetically modified foods is highly unlikely (FAO/WHO, 2000):
In considering the issue, the consultation noted that very little is known about the potential of long term effects of any foods. In many cases, this is further confounded by wide genetic variability in the population, such that some individuals may have a greater disposition to food-related effects. In this context, the consultation acknowledged that for genetically modified foods, the premarketing safety assessment already gives assurance that the food is as safe as its conventional counterpart. Furthermore, it was recognized that observational epidemiological studies would be unlikely to identify any such effects against the background of undesirable effects of conventional foods.
• Environmental Monitoring. Genetic modification of plants through plant breeding is well established as a major contributor to increased yield and value addition to our food and feed supply. Plant breeding is conducted in both the public and private sector, with the private sector in recent years dominating the major crops, e.g., corn, cotton, sorghum, and soybeans. Extensive field testing involving multiple sites and several years typically occurs before seed multiplication and release of a commercial seed product. Most states test and release public varieties in a tracked process that produces certified seed. Most states also provide public testing in a fee-based evaluation at a few sites. Private-sector seeds are sometimes submitted for public testing, but usually undergo similar field evaluations and, in the case of large seed companies, may be tested at hundreds of sites.
The ultimate test in all cases is in commercial farmers’ fields. Almost all farmers monitor their crops from planting to harvest by regular field examinations. This key monitoring activity is done by the growers or, in the case of large acreage, may be performed by hired consultants or scouts. Consultants or scouts are frequently used for cotton but are less common for soybeans. This “on-the-farm” monitoring follows emergence, growth, nutrient limitations, flowering, fruit set, maturation, insect pests, disease, weed control, and other key events. Finally, the yield for each crop in each field is measured at harvest. The experience of the farmer or consultant for specific crops in specific locations represents a baseline. In addition to the farmers and consultants, there are also extension agents and industry representatives who do a modest amount of monitoring.
Monitoring by the farmer or hired consultant has proven to be effective and serves as the first alert for untoward effects. For example, farmers were the first to identify herbicide-tolerant weeds, e.g., atrazine-resistant pigweed in Ontario in the 1950s to 1960s. Untoward environmental or performance effects of rDNA biotechnology-derived seeds—as is the case for traditional seeds—would normally be identified by the farmer or consultant. Examples are the reduced boll set of herbicide-tolerant cotton in the Mississippi delta in the introductory year of this product, as well as periodic herbicide performance problems. Special monitoring by the seed company is required for Bt crops to provide early identification of Bt-resistant insect pests (Anderson, 1999). The farmer and consultant monitors, however, are likely to provide an early alert for actual pest resistance.
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The road map for rDNA biotechnology-derived seeds from initial generation through testing and regulatory approval is similar to that for traditional seeds, with additional steps to meet regulatory requirements. To date, almost all the commercialized rDNA biotechnology-derived seeds have been developed by the private sector, with four large firms as the primary technology developers. From several hundred up to a thousand transformants with the desired gene or trait, one or a few are selected for development. The selected transformants are evaluated for efficacy in standard (e.g., Crocker 305 in the case of cotton) and other genetic backgrounds, agronomic characteristics (e.g., maturity, vigor, standability), and genetics (e.g., single gene, stability, purity). Equivalency testing is performed at multiple locations by the seed company. In addition, the rDNA biotechnology-derived seed is analyzed to provide data for regulatory review.
Questions remain as to long-term effects on organisms (e.g., birds, plants, animals) and microorganisms in the environment. These questions are the same as those that need to be raised for introducing any new types of plants or even new varieties of an established plant. Hypothetical deleterious changes in producing modified foods are possible, as such changes have occasionally occurred in nature and in conventional plant breeding. Such plants rarely make it to the marketplace and, if they do, can be readily removed. With a higher degree of regulatory oversight for all foods derived by rDNA biotechnology, there is less likelihood of adverse reactions to consumers than with conventional foods. rDNA biotechnology will require continued research and management, as well as monitoring and surveillance, to produce high-quality and affordable foods.
Food allergies involve abnormal immunological responses to substances in foods, usually naturally occurring proteins. The majority of food allergies are traced to eight commonly allergenic foods or food groups: milk, eggs, fish, crustacea, peanuts, soybeans, tree nuts, and wheat (FAO, 1995), although other sources of genetic material can possess genes encoding for environmental allergens such as pollen allergens. Allergic reactions can be manifested by symptoms ranging from mild cutaneous or gastrointestinal symptoms to life-threatening anaphylactic shock reactions. Virtually all food allergens are proteins, although only a small fraction of the proteins found in nature (and in foods) are allergenic. Since genetic modifications involve the introduction of new genes into the recipient plant and since these genes would produce new proteins in the improved variety, the potential allergenicity of foods developed through rDNA biotechnology has been a source of some concern. (This topic is also discussed in the Safety section.)
Despite the concerns, no unique allergic reactions have yet occurred to any of the foods derived through rDNA biotechnology. Of course, a consumer with a soybean allergy is likely to be reactive to an rDNA biotechnology-derived soybean as well. But no new and novel allergens have been introduced into foods through rDNA biotechnology. In fact, the proteins introduced into rDNA biotechnology-derived foods to confer traits such as insect resistance and herbicide tolerance are unlikely to be allergenic because they are expressed at very low levels in the modified food, they have no amino acid sequence homology to known allergens, and they are readily digested (Astwood et al., 1996; Harrison et al., 1996; Metcalfe et al., 1996).
The potential allergenicity of rDNA biotechnology-derived foods can be assessed using a decision-tree strategy developed by the International Food biotechnology Council (IFBC) and the Allergy and Immunology Institute of the International Life Sciences Institute (ILSI) in 1996 (Metcalfe et al., 1996). The utility of this approach was recently recognized by FAO/WHO (2000). This strategy focuses on specific scientific criteria, including the source of the gene(s), the sequence homology of the newly introduced protein(s) to known allergens, the immunochemical reactivity of the newly introduced protein(s) with immunoglobulin E (IgE) antibodies from the blood serum of individuals with known allergies to the source from which the genetic material was obtained, and the physicochemical properties (e.g., digestive stability) of the introduced protein (see discussion in the Safety section).
If genes are obtained from known allergenic sources, the possibility of the transfer of a known allergen must be carefully examined. The potential hazards are illustrated by the case of a soybean variety constructed to correct the inherent methionine deficiency existing in soybeans. A high-methionine protein was introduced into soybeans by one firm using a gene from Brazil nuts. Brazil nuts are known to be allergenic, but, at the time of this development, the allergens from Brazil nuts had not been identified. The high-methionine protein from Brazil nuts was identified as the major allergen in research sponsored by that firm (Nordlee et al., 1996). As a result, commercial development of that particular soybean variety ceased.
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Antibiotic Resistance Transfer
Genetic transformation of plant cells is an inherently infrequent event. The challenge that the researcher faces is to identify the few cells that have integrated the introduced DNA from a large population of non-transgenic cells. This is most often done by introducing a selectable marker that permits growth of only cells containing the newly introduced DNA. In plant transformation, a gene for resistance to the antibiotic kanamycin dominated early rDNA biotechnology-derived crops (see the Safety section for additional information).
Concerns have been raised about the potential for horizontal gene transfer of the antibiotic resistance gene from an rDNA biotechnology-derived plant to microorganisms, thereby reducing the efficacy of the antibiotic. However, both scientists and most regulators around the world generally believe that this risk is virtually nonexistent. The conclusion derives from a number of facts. First, the marker gene has been altered to express in plant cells. Even though, as discussed in the Introduction section, genes are not unique to specific organisms, the controlling elements that permit gene expression are very different in plants and microorganisms. One would not expect that a gene engineered to work optimally in plant cells would work effectively in bacteria. Second, the antibiotic-resistance genes are stable when integrated into plant DNA. Plant DNA, upon exposure to the gastrointestinal environment, would be rapidly hydrolyzed to small, nonfunctional pieces long before it came into contact with microflora. Third, DNA uptake into bacteria is an extremely inefficient process requiring either transformation competence or specific DNA transfer mechanisms employed between bacteria. There are no known mechanisms for transfer of DNA from plant cells to bacteria, and the bacteria in the digestive system would not be competent to take up free DNA.
Fourth, even if such mechanisms for DNA uptake were in place, stable integration of that DNA into bacteria requires extensive DNA sequence homology between the incoming DNA and the host chromosome. Such homology would not exist unless bacteria already possessed the antibiotic resistance gene prior to DNA uptake. Fifth, even if such unlikely transfer were to occur, positive selection pressure would be required; e.g., the person would have to be taking the antibiotic to which the resistance was encoded at the time of such transfer. Finally, there are no authenticated reports of any horizontal DNA transfer occurring from food plants to bacteria within the gastrointestinal tract of humans. Even if this occurred by some unknown mechanism at some vanishingly small frequency, there would be no consequence, because of the existing level of antibiotic resistance already present in gut microflora.
A recent FAO/WHO joint consultation (FAO/WHO, 2000) addressed the concern that there might be transfer of antibiotic resistance from the widely used antibiotic resistance marker genes and concluded that no health risk is presented:
The Consultation considered horizontal gene transfer from plants and plant products consumed as food to gut microorganisms or human cells as a rare possibility, but noted that it cannot be completely discounted. The most important consideration with respect to horizontal gene transfer is the consequence of a gene being transferred and expressed in transformed cells. The Consultation further noted that the antibiotic resistance markers currently used in genetically modified plants have been previously reviewed for safety. It has concluded that there is no evidence that the markers currently in use pose a health risk to humans or domestic animals.
In addition, non-antibiotic resistance markers have mainly replaced kanamycin in products now in the pipeline. These include removable selectable marker genes such as using the Cre-lox site-specific recombination system or transposable elements. Cre is a recombinase; lox is a 32-base-pair recognition site. Positive selection systems will probably dominate in the future. One system (termed BOGUS) uses an exclusive energy source, cellobiuronic acid, a disaccharide that, when transported into the cell, is metabolized to glucose by beta-glucuronidase. Another example involves the use of phosphomannose isomerase (PMI). Plant cells without this enzyme are unable to survive in a tissue culture medium containing mannose-6-phosphate as a sole carbon source.
Concerns with Naturally Occurring Toxicants
The great majority of food plants, and many animals used for food, produce or carry naturally occurring toxic substances (IFBC, 1990; Liener, 1980; NAS, 1973). The only categories of organisms used as human food that have essentially no or only a very rare content of naturally occurring toxicants are the cereal grains and domestic animals. Even among these, an exception must be made for milk, discussed below. The absence of toxicants from these food sources is entirely due to man’s interference with nature—millennia of selective breeding and centuries of careful husbandry have reduced their original toxicant content. Plants, and many animals, produce toxicants for a variety of reasons. Some kill or repel predators, pests, or diseases (Ames et al., 1990a, b). Others are pollenator attractants. Some inhibit competitive species. Others are metabolic “dead ends”— a means for a plant to sequester a plant toxicant it can neither avoid nor excrete (IFBC, 1990). While the vast majority of toxicants occur at levels so low that they carry no threat to human safety, there are more than twenty for which there are well documented reports of human injury or death from their consumption in or on food (IFBC, 1990).
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The largest known number of naturally occurring toxicants are endogenous, or “constitutive”; i.e., they are produced by the normal metabolic processes of the organism that is the food source. An example is solanine, a neurotoxin in potatoes that has been the cause of numerous outbreaks of human poisoning when potatoes were grown under unfavorable conditions or when they formed a large part of the diet. Another example is cyanogenic glycosides, found in several foods such as lima beans and bamboo shoots. In these and other crops, conventional breeding has been used to decrease toxicant levels.
Another group that has received much scientific and regulatory attention is the “acquired” toxicants. These are formed in or on food as the result of naturally occurring processes, which can often be minimized but never eliminated. An example are the mycotoxins, such as the aflatoxins, caused by mold contamination. Aflatoxin B1, in combination with hepatitis B, is responsible for the very high levels of liver cancer found in the Qidong region of China (Qian et al., 1994; Wang et al., 1999). Susceptibility of plants to mold infections is affected by both genetic and environmental factors.
A third group, only known within the past few decades, is the “derived” toxicants. These occur in food as a result of storage or normal, traditional processing. Examples are the highly mutagenic and carcinogenic polynuclear aromatic amines formed in meats and other foods by conventional roasting, baking, or cooking. Although a risk is clearly present, the size of that risk and the extent of actual human harm, if any, from their consumption are as yet unknown.
A fourth group is the “pass-through” toxicants that occur in food as a result of being acquired by the food organism from its own environment or food supply. The organism that becomes or provides the human food is simply a passive vehicle. Although extremely rare in modern times, the toxicants that occur in milk and honey provide examples of human deaths, among them that of Abraham Lincoln’s mother (IFBC, 1990; Liener, 1980; NRC, 1996).
Given the near ubiquity and occasional demonstrated harm from toxicants that are naturally and unavoidably occurring in most traditional food sources, it is entirely rational to take every reasonable precaution to assure that breeding—by either traditional or rDNA biotechnology methods—does not result in an increase in risk and, if possible, decreases any risk.
L-tryptophan for food and feed use, manufactured by bacterial fermentation, is contaminated by a number of secondary substances. These impurities are removed by treatment with activated carbon and reverse osmosis. A Japanese manufacturer in late 1988 and early 1989 made a number of simultaneous changes in manufacturing, including the use of a genetically engineered organism, Bacillus amyloliquefaciens, to increase production of L-tryptophan. At the same time, the purification procedure was altered by eliminating reverse osmosis and reducing the amount of activated carbon used. The illness of 1,500 people and the death of 37 in the U.S. from eosinophilia-myalgia syndrome from consumption of this L-tryptophan has been incorrectly attributed to the rDNA biotechnology-derived organism, rather than to the failure to perform standard purification to remove impurities. In three lawsuits, there was overwhelming evidence that the rDNA biotechnology-derived organism was not responsible for the illnesses and deaths (Hill et al., 1993; Kilbourne et al., 1996 Philen et al., 1993).
A number of issues have been advanced by some scientists and opponents of rDNA biotechnology-derived foods as major environmental or human health risks. Examination of all the science eliminates or diffuses many of these so-called risks. Other suggested risks are less severe, or no more severe, than those risks associated with the more conventional breeding techniques that have been practiced for centuries. This body of science leads to the conclusion that there is no increased adverse environmental effect inherently attributable to the use of rDNA biotechnology in food production. There is some evidence of overall improved environmental safety due to wider use of rDNA biotechnology. That is not to say that all rDNA biotechnology-derived products will be safe—they must be examined on a case-by-case basis before being commercialized.
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Many of the environmental and consumer groups that have been pressing for stronger regulatory controls are also concerned about the effects of market power in the agricultural biotechnology industry. While rigorous testing and evaluation are required for any new item introduced into the food supply, adding unnecessary time-consuming and expensive testing requirements will only increase the pressure for consolidation in the industry, while creating new barriers to entry for small start-up companies. The agricultural biotechnology industry would benefit from a regulatory system that increases consumer confidence in the safety of rDNA biotechnology-derived food products and provides support for claims regarding the health benefits of rDNA biotechnology-derived foods with enhanced nutritional qualities.
Based on its evaluation of currently available scientific information, the Benefits and Concerns Panel concluded that further development and use of food rDNA biotechnology provides a number of benefits:
• A more abundant and economical food supply for the world.
• Continued improvements in nutritional quality, including foods of unique composition for populations whose diets lack essential nutrients.
• Fresh fruits and vegetables with improved shelf life.
• Foods with reduced allergenicity.
• The development of functional foods, vaccines, and similar products that may provide health and medical benefits.
• Further improvements in production agriculture through more efficient production practices and increased yields.
• The conversion of nonproductive toxic soils in developing countries to productive arable land.
• More environmentally friendly agricultural practices through improved pesticides and pesticide usage practices, less hazardous animal wastes, improved utilization of land, and reduced need for ecologically sensitive land such as rain forests.
With regard to a number of environmental and economic concerns about rDNA biotechnology-derived food products, the Benefits and Concerns Panel reached the following conclusions:
• New rDNA biotechnology-derived foods and food products do not inherently present any more serious environmental concerns or unintended toxic properties than those already presented by conventional breeding practices, which have an impressive safety record.
• Appropriate testing by technology developers, producers and processors, regulatory agencies, and others should be continued for new foods and food products derived from all technologies, including rDNA biotechnology.
• Programs should be developed to provide the benefits of safe and economical rDNA biotechnology-derived food products worldwide, including in less-developed countries.
Anthony Artuso, Assistant Professor, Dept. of Agriculture, Food and Resource Economics, Rutgers University, New Brunswick, N.J.
Dennis Avery, Director of Global Food Issues, Hudson Institute, Churchville, Va.
Roger N. Beachy, President, Donald Danforth Plant Science Center, St. Louis, Mo.
Peter R. Day, Director, Center for Agricultural Biotechnology, Rutgers University, New Brunswick, N.J.Owen R. Fennema, Emeritus Professor of Food Science, University of Wisconsin, Madison
Ralph Hardy, Boyce Thompson Institute for Plant Research, Inc., Clarence Center, N.Y.
Peter L. Keeling, Research Director, ExSeed Genetics LLC, and Associate Professor of Agronomy, Iowa State University, Ames
Todd R. Klaenhammer, NCSU Distinguished Professor, William Neal Reynolds Professor, Food Science and Microbiology; Director, Southeast Dairy Foods Research Center, North Carolina State University, Raleigh
Martina McGloughlin, Director, Biotech Programs, University of California, Davis
Anne K. Vidaver, Professor and Head, Dept. of Plant Pathology, University of Nebraska, Lincoln
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