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Biotech Breakdown
by Susan D. Borowitz
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).
GE CONSTRUCTS
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.
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