Antibiotic Resistance Genes

One area of concern regarding genetically engineered crops is the possibility of antibiotic resistance genes being transferred to harmful bacteria.

When a genetic engineer inserts a new gene into a plant's genetic code, she does not just insert one gene. Most new genes are linked with a second gene, a "marker" gene. While the inserted genes can code for a number of things, the marker gene is usually a gene for antibiotic resistance. This is done so the genetic engineer can easily see if the desired gene has been encoded. One only need run tests with bacteria and an antibiotic to see if the marker gene, as well as its counterpart are present.

But problems can arise from this. There is the possibility that the antibiotic resistance gene will find its way from a plant into a bacteria. Conceivably this could happen if a human or animal were to eat genetically modified food. Resident bacteria in the stomach could pick up the gene for antibiotic resistance. This could have disastrous consequences if the stomach bacteria transferred the gene to the bacteria the antibiotic is supposed to kill. If those bacteria were the type that attacked humans, animals, or plants, the result would be widespread infection and no way to treat it. (The Royal Society, September 3 1998)

Antibiotic resistance genes can be transferred in other ways besides in the stomach. In 1994 a study was done using genetically engineered oilseed rape (an ingredient in canola oil) black mustard, thornapple, and sweet peas. All four crops had antibiotic resistance genes. These crops were grown with a fungus, Aspergillus niger, or their leaves were added to the soil surrounding the fungus. All follow-up co-culture experiments found that the fungus had become antibiotic resistant as well.( Friends of the Earth)

Herbicide Resistance Genes

A second concern in the area of gene transfer deals with herbicide resistant genes being encoded into crops and then being unintentionally transferred to weed species.

Worldwide, 50 million hectares are planted with genetically modified crops, an area equal to the size of Germany. ("Biotech Goes Wild" Technology Review, July/August 1999) Two-thirds of these crops are engineered to be herbicide resistant. One third of the soybeans grown in the United States are Roundup Ready soybeans.("Biotech Goes Wild" Technology Review, July/August 1999)

The advantage of creating herbicide resistant crops is that a farmer can spray weedkiller all over a field, destroying the weeds, but not harming the crops at all. But there is great concern about an unintended side effect of creating herbicide resistant crops. The genes for herbicide resistance could be transferred from crops to weedy relatives of those crops. The result would be a weed resistant to herbicide, and conceivably flourishing out of control. Even worse, is the possibility of "superweeds," pests that have picked up genetic resistance to several herbicides from genetically modified crops.(The Royal Society, September 3 1998)

Initially, scientists believed anti-herbicide genes would not flow from crops to weeds because crop-weed hybrid plants, which would carry the genes, would die out because hybrids do not tend to flourish. ( New Scientist, 15 August 1998) But there is much recent evidence to suggest that herbicide-resistant genes can be transferred from genetically engineered crops to other plants.

For example, in 1998 researches studied genetically modified mustard plants. This species of mustard typically self-pollinates, so it was assumed that there was little chance of the plant's genes being transferred to another organism. The researches then planted the normal variety of this mustard plant, a version genetically modified to be resistant to herbicides, and a naturally occurring version of the mustard plant that had herbicide resistance. The surprising results were that the genetically engineered plants were 20 times more likely to transfer their genes to other plants than the naturally occurring resistant plants were. ("Biotech Goes Wild" Technology Review, July/August 1999)

Earlier in 1996, Danish scientists noted that the genetically engineered Brassica napus was breeding with its weedy relative Brassica campestris. The result of this breeding were plants that looked like Brassica campestris but were herbicide resistant like Brassica napus had been engineered to be.("Biotech Goes Wild" Technology Review, July/August 1999)

Footnotes

The Royal Society, September 3 1998

Friends of the Earth

"Biotech Goes Wild" Technology Review, July/August 1999

New Scientist, 15 August 1998

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