Introduction
As the power for weaving the fabric of life is newly placed in the trembling
hands of humanity it is crucial to insure the intentions of researchers and developers
do not unleash Pandora’s box upon the world. The development of new methods
to detect the presence and possible spread of transgenic foods is vital in monitoring
the safety of genetically modified foods. The development of new tools to quickly
identify detrimental genes will also prove invaluable as mankind attempts to tame
the dangers already present in our own gene pool.
Why We Modify Foodstuffs
Food products have been altered in many
ways to improve product yields and nutritional values. The protein product of
the gene Bt in the bacteria Bacillus thuringiensis has been found to paralyze
the digestive systems of many species of insects and has been built into the plants
themselves. If certain pests eat these plants they will soon die of starvation
no matter how much they eat. Plants have been created which not only have built
in insecticides, but are also resistant to herbicides. Roundup is extremely effective
in killing most plants by inhibiting 3-enolpyruvylshikimate 5-phosphate (EPSP)
synthetase in the Aromatic Amino Acid Pathway. The herbicide doesn’t spread
far from where it is sprayed, which is beneficial for wildlife and water supplies
surrounding the farmlands. Roundup wasn’t previously sprayed on crops: It
would kill all of them along with the weeds. Fortunately, genes of other bacteria
possess an immunity to Roundup due to their altered EPSP synthetase. The genes
for this altered pathway have been inserted into plants making them immune to
Roundup. After genetically modifying the crops, Roundup can be sprayed directly
on farmlands, eliminating all weeds without endangering the harvest. Beef and
milk products are even being made more nutritious with insertion of new enzymes
into the animal genomes.
Grass-Roots Resistance
There is a large amount of public resistance
to the use of these genetically modified foods. Protestors of these "Frankenfoods"
have slashed farms in Europe. Most supermarkets in Europe either won’t sell
transgenic food or are required to label them. The rejection of these products
in the US has been nowhere near the severity seen in Europe, but organizations
such as Friends of the Earth and the Sierra Club are attempting to rally the public
to the same outrage.
There are many objections to the foods.
People fear the government has not done enough tests on the food to insure their
safety. Just as bacteria are able to acquire resistance to antibiotics by transferring
plasmids, there is a concern about the transference of these super-genes to weeds
and bacteria. An unconfirmed rumor about transgenic potato genes being spread
to laboratory rats caused the production of those potatoes to be halted until
further tests could be done. Some transgenic plants have a resistance to ampicillin.
It is feared this resistance could enter the genome of infectious bacteria and
provide them resistance to the drug. If the weeds were somehow able to obtain
genes through the pollen of engineered plants, they would become very difficult
to kill. People even doubt the effectiveness of the insect-proof plants over time
and believe meddling with nature will only produce a conduit through which our
present means of defending crops will be lost, or worse, intercepted by "the
enemy."
Detection of Modified Foods
The need to detect these transgenic foods
arises from several areas. Detection of the transgenic vectors is necessary to
determine if the engineered traits are indeed being passed to other species. Detection
would also be used to single out transgenically produced products to the purchasers
of the goods. This identification would help insure the modified products are
being properly labeled for sale where required. Imported transgenic crops can
be easily identified and regulated as well.
A couple methods of detecting transgenic
products are commonly used. The first utilizes immunoassays. Immunoassays are
constructed to find the presence of a specific molecule, in most cases a protein.
Assays to detect transgenic proteins must be made with an idea of what types of
proteins are unique to genetically modified organisms (GMO’s). First, these
altered GMO proteins are injected into a lab animal. Then the animal’s immune
system forms antibodies to the foreign protein, just as your body produces antibodies
to a foreign invading pathogen such as a cold virus. To isolate the particular
antibodies, the spleen cells are removed from the animal. The spleen cells are
chosen because that is the source of a large number of antibody-producing cells,
called B cells. These B cells are then fused with cancerous myeloma cells. This
type of fusion is called hybridization and produces a cell containing genetic
material from both cells. The result is a cell possessing both the immortality
of a cancerous cell and the antibody production of a B cell. The hybridized cells
are screened to isolate the hybridoma clone that produces an antibody of single
specificity for the transgenic protein. These cells can be used to produce large
amounts of the antibodies that will bind specifically to the transgenic protein.
Because the hybridized cells only produce one type of antibodies, they are called
monoclonal antibodies.
The immunoassay to detect the transgenic
antibody is formed by bonding these antibodies to a polymer support. The antibody-lined
polymer support is washed to remove unattached antibodies and exposed to the suspected
transgenic proteins. The support is then blocked so no other proteins can bind
to it. A ground-up sample of the food in question is added to the assay. The antibodies
on the solid support will retain any transgenic proteins matching the antigen
to which they were designed to bind. After this step, another wash will remove
any unbound proteins, as these were not recognized by the affixed monoclonal antibodies.
A second antibody is then introduced that also recognizes the transgenic antigen
and bind to it. This forms a "sandwich" of the first and second antibodies
around the antigen. Another wash is done to remove any unbound secondary antibody.
This secondary antibody is significant because it is tagged with either a fluorescent
label or an enzyme that will react to certain dyes and their color. Either way,
any fluorescence or color change (upon addition of the color-producing dye) will
indicate the presence of transgenic material in the foods tested. If no color
is generated, then the food is unmodified.
A more accurate and increasingly popular
method is the use of polymerase chain reactions (PCR). PCR is a method for amplifying
specific segments of DNA from a large pool of genetic material. Primers are added
to the PCR reaction that will recognize and bind to sequences found only in the
transgenic genes. In this manner, the PCR reaction will amplify transgenic DNA,
and indicate its presence when an investigator visualizes any DNA that was amplified
by gel electrophoresis. PCR also provides greater sensitivity. The chance of the
primer attaching to the wrong site is extremely low whereas similar proteins may
attach to the same antibody in some cases. The possibility for amplification of
a signal is much greater with PCR since the process amplifies its results every
time it is allowed to cycle. Immunoassays are limited in the number of tags that
can be attached to a single antigen. There is also the risk that the transgenic
protein is not being synthesized in large amounts or at all during the collection
of the immunoassay samples. PCR, in interacting directly with the DNA, bypasses
these risks.
Conclusion
Genetically modified foods offer the world
new possibilities beyond more nutritious food and better crop yields. Plans are
currently underway to put vaccines in the plants of underdeveloped nations. Although
the concerns of the critics of transgenic food are viable the probability of genetic
transfer between higher eukaryotic organisms is incredibly low, there is a much
greater chance of natural evolution enabling unwanted plants to develop resistance.
Nonetheless, the technology used to detect genetically modified organisms will
come of great use to help insure the genes constructed to benefit society are
not to its detriment. The development of new tools to quickly identify detrimental
genes will also prove invaluable as mankind attempts to tame the dangers already
present in our own gene pool. Not only does the detection of transgenic genes
keep science in check for today, but also may help to develop a means of quickly
identifying any dangerous genes, such as those leading to Parkinson’s and
Alzheimer’s disease as we approach a future where they will be correctable.
GM Foods and Their Detection Web Site Links
Genetic ID: Identifies
transgenic products
Cambridge
Scientific Abstracts - genetically modified foods and their potential negative
impacts
Intekom:
US Chemical Giant Monsanto Wields Control
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