From: Terrain Summer 2000 - the Magazine of the Berkely Ecology Center.
Over the past few years, scientists have become increasingly concerned about the ecological effects of genetically engineered (GE) crops. For the most part, these involve how a plant will interact with other organisms, for example killing monarch caterpillars or creating superpests. But there is another level of concern. According to a growing number of scientists, the imprecise methods of genetic engineering may allow foreign, inserted genes to interact with bacteria or viruses, with alarming side-effects possible. Though we don't know the odds that any of these will occur, the possibilities are inherent in the process.
The biotech industry claims that agricultural biotechnology is just a simple matter of inserting a new gene, one that will give a desired trait, into a plant. The reality is much more complicated - and risky. To bring about a desired trait in a plant, biotech researchers add a gene from an unrelated plant, or even from a bacterium, a virus, or an animal - organisms that normally would never cross-breed with the plant. The biotech companies have given lip service to making plants more nutritious or better-yielding (the specious 'feed the world' argument [see page 8]), but that hasn't happened much. The goal is usually to make the plant resistant to viruses, able to produce its own insecticide, or able to resist the company's own herbicide.
As we have heard, these practices may have serious ecological consequences. [See Terrain Winter '98 through Spring '00.] If all we had to worry about were terminator seeds, more herbicide use, superpests, superweeds, insect deaths, or the destruction of organic farming's main pesticide, that would be enough. But the desired gene is just one part of an intricate package in a complex process - one with a Pandora's Box of possible consequences. In genetic engineering, scientists create a package of several genes from bacteria and viruses, splice them together as a unit, and insert them into an organism. The additional genes have two functions: They help break down the natural barriers between species. They also make sure that the desired gene, once inserted, is actively expressed.
Many of these genes come from bacteria and viruses, and have never before been in our diets, our food-animals' diets, or in the environment in these specific combinations, or in such large numbers. Biotech companies test only for known allergens, not for any new allergens, toxins, or pathogens. And the new genes could interact with genes already present in plants, with unpredictable consequences. Like any complex organism, a plant contains genes other than its own. It will harbor a flotilla of microbes, including bacteria that can promiscuously exchange genes. Any of these microbes could exchange genes to create new pathogens. Many scientists have dismissed this process, called horizontal gene transfer (HGT), as occurring so infrequently with non-related species as to be trivial. Until very recently, scientists thought that 'horizontal' transfer of foreign genes into plants was very rare or non-existent. But in 1998, biologists at Indiana University reported finding that genes from a fungus had invaded 48 different kinds of nearby plants. The next year, molecular biologists at the Austrian Academy of Sciences reported that genes from a previously unknown virus had repeatedly integrated themselves into the genes of tobacco plants. (Both studies were reported in the Proceedings of the National Academy of Sciences.) Research is making it increasingly clear that genetic material can be transferred among organisms incapable of mating with one another - that 'horizontal' transfer of genetic material into plants from viruses, bacteria, and unrelated plants can and does occur. The problems begin, then, when people start mixing genes in combinations not found in nature. Hundreds of scientists have become concerned enough to sign an 'Open Letter from World Scientists to All Governments,' calling for the 'immediate suspension of all environmental releases of GM (genetically modified) crops and products.' That petition can be found on the web site for the Institute of Science in Society . This organization is led by Dr. Mae-Wan Ho, of the UK's Open University, and author of the book Genetic Engineering: Dream or Nightmare? (reviewed in Terrain, Spring '99).
Genes provide the instructions for every living thing to be alive. Every cell contains long molecules called DNA, divided into sections called genes, each of which contains instructions for a particular characteristic. In traditional plant breeding, farmers mate two closely related organisms with specific traits. Farmers simply select which offspring to breed, a straightforward process. To splice in new genes is an entirely different matter. Scientists have to build a tool to trick plant cells into accepting and incorporating genes from unrelated species (see below, 'GE Techniques'). The desired gene doesn't come unaccompanied. It's like a remote-controlled toy car - it won't do anything unless a controller tells it to. That controller is called a 'promoter,' a device that turns on when a gene needs to talk to all of the other genes, allowing the organism to work as a whole.
Biotechnologists need a promoter that's very active, and for that they rely on the promoter from the Cauliflower Mosaic Virus (CaMV). This promoter works with almost any gene, not just the genes from that particular virus. The CaMV promoter, which has been placed in virtually all transgenic crops on the market, can be likened to a remote control powered by a high-voltage car battery. It's always on, it's robust, it can control any toy truck - and it will tell that truck to go, go, go all the time.
The problem is, the CaMV promoter is more complicated than just an on-off switch; it sends out such a strong signal that it may control not only the new gene it's inserted with, but also other genes that are already in the plant, with unpredictable results.
This promoter is at the root of the horizontal gene transfer problem. Even after it's inserted, it is very good at separating out from the plant's chromosomes and recombining with other genes, such as ones for dormant viruses already in the plant (genetic remnants of an infection), or bacterial genes added as part of the GE process. Instead of the promoter telling a new red-car gene to go, go, go, it is now connected to an orange monster truck, in a combination that has never existed before, with unknowable effects.
The CaMV promoter gene can exacerbate any problems associated with horizontal gene transfer. According to Michael Hansen, a research associate at Consumers Union, organisms normally protect themselves from horizontal invasions of genetic material by chemically 'silencing' the new genes. When promoters are added to the mix, however, this defense is much less effective. In fact, one of the main reasons the CaMV promoter is added is to overcome the plant's natural 'gene silencing' defenses. In short, the CaMV promoter is an unstable piece of genetic material, prone to recombine with other genes found in the plant, including dormant viruses often present in a plant's genetic make-up. Now, given that this promoter is present in all commercial transgenic crops, and that genes can be horizontally transferred into and out of plants, scientists like Ho, University of Western Ontario's Joe Cummins, and Open University's Angela Ryan suspect that promoter genes could recombine with genes from bacteria, viruses, and dormant viruses to create new pathogens.
A third type of genetic component adds to the risks of agricultural biotechnology. Added along with the desired gene and the promoter gene, a marker gene lets scientists identify which plant cells have been successfully transformed with the new genes. In a holdover from the days when these practices were strictly limited to the lab, corporate biotechnologists typically use genes that code for antibiotic resistance. When they apply the antibiotic to the cells they're working with, only the ones that have successfully integrated the new genes will survive the dose. The marker gene remains part of the plant's genetic make-up thereafter, conveying antibiotic resistance. For this step, biotech companies mostly make use of kanamycin, an antibiotic rarely used in the developed world, but a drug of last resort for tuberculosis. Newer GE varieties are being based on resistance to ampicillin, an antibiotic much in use. Already, five countries in Europe have banned planting of corn containing ampicillin resistance, fearing that this trait could spread to bacteria and so make it harder to treat infections. Bacteria that are resistant to antibiotics are an increasing problem. Through horizontal gene transfer, the resistance could spread to other bacteria, making it harder to treat disease. In 1999 the British Medical Association called for an immediate halt to the use of antibiotic-resistance genes as markers. GE Techniques So, we have our desired gene, our promoter genes, and our marker gene. How to get these into the plant? Scientists take advantage of gene carriers or vectors, made of bits of viruses and other genetic parasites such as plasmids, small circular pieces of genetic material that live and replicate themselves within many bacterial cells, separately from the main chromosomes. These vectors have a talent for breaking into cells and integrating into the cell's own genetic material, making cells express the genes that are smuggled in. Scientists take these vectors and splice in all the genes we've mentioned above - the desired gene, the marker gene, and promoter genes. Then they let the vector do the work, invading the target cells and depositing the new genes into the cell's genome. The most frequently used vector is the T DNA, which is part of the 'Ti' (tumor-inducing) plasmid of Agrobacterium, a soil bacterium.
Grass-like plants (monocots such as corn and other grains) are resistant to infection by this bacterium, however, so for these plants, biotechnologists use 'gene guns.' They take microscopic particles (gold or tungsten) that have been covered with DNA, and literally shoot the mixture directly into plant tissues. This often results in insertion of multiple copies of the new genetic construct, which may exacerbate the harmful and unpredictable effects. In one case, according to the International Journal of Food Science and Technology, duplicate genes caused a strain of GE yeast to become mutagenic. [See Terrain Spring '00.]
There are additional risks associated with GE organisms:
* In splicing genes that make a plant resistant to viral diseases, biotech scientists can inadvertently create new, potentially deadly viruses.
Viruses consist of genetic material covered by a protein coat. For an unknown reason, when scientists insert the genes for a virus's coat protein into a plant's genetic make-up, the plant can resist a virus it had been susceptible to. That situation, however, also makes it theoretically possible for the plant to generate new live viruses through several processes, one of which is 'transcapsidation.' In that process, the genetic material from one type of virus becomes enveloped in the protein coat of another kind. With the splice, the plant has been given a gene for a new virus protein coat. Any virus that happens by could try on the protein coat. A virus wearing someone else's coat could infect an individual that would normally recognize and resist it, since resistance is based on the coat, not the innards. Another process is genetic recombination, in which the coat-protein or other viral gene joins up with infecting viruses to generate new viruses. This has happened in the laboratory and superinfectious viruses have resulted, according to Ho, Ryan, and Cummins. * Scientists have long assumed that any bits of naked DNA entering our digestive systems would be demolished by enzymes, but recent research puts that into question. When researchers at the University of Cologne, Germany, fed viral DNA to mice, they found that large fragments resisted digestion and even entered the bloodstream. Even after processing, GE foods may contain genes that we haven't been eating regularly before, some of which code for antibiotic resistance. What if the resistance genes are taken up by the many benign bacteria that live in our digestive tracts, which are then free to transfer those resistance genes to pathogenic bacteria? Furthermore, once the DNA is passed into the bloodstream, Mae-Wan Ho posits in the most far-reaching of her conclusions, it could be taken up and integrated into the DNA in a cell, where 'a range of harmful effects may result including cancer.'
These risks are too great, given the scant benefits available from GE foods and the fact that any potential benefits can be accomplished through far safer farming methods. That is why more than 250 scientists from 34 countries are calling for the 'immediate suspension of all environmental releases of GE crops and products; for patents on life forms and living processes to be revoked and banned; and for a comprehensive public enquiry into the future of agriculture and food security for all.'
East Bay writer Susan D. Borowitz studied graduate-level ecology at the University of California at Davis.
For full references and footnotes to this article, call (510) 548-2235 or email terrain@ecologycenter.org.
© 2000 Susan D. Borowitz.
Article first published 31/7/00
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