Researchers at New York University have found that insect-killing toxin from Bt corn is released into soil from the roots. The scientists say more research is needed to determine whether this exuded toxin has a good, bad, or neutral effect on organisms in soil.
The research was conducted by NYU biology professor Guenther Stotzky, NYU research scientist Deepak Saxena, and Saul Flores of the Venezuelan Scientific Research Institute. The team's findings were published in the December 2nd issue of Nature in a brief communication entitled, "Insecticidal toxin in root exudates from Bt corn."
Bt corn is corn that has been genetically modified to produce an insecticidal toxin derived from the bacterium, Bacillus thuringiensis (Bt). The toxin is present in the plant's tissues and kills the larvae of caterpillars that attack the plant. It was previously believed that the Bt toxin molecule was too large to be released through the plant's root system. Recently it was shown that the toxin is also present in the pollen of Bt corn and that when the pollen was placed on the leaves of milkweed, it killed monarch butterflies that ate the contaminated leaves.
Professor Stotzky said, "We have no indication of how soil communities might be affected by the Bt toxin that these plants exude. It might improve control of insect pests. It might enhance the rate at which insect pests become resistant to the toxin. It might negatively impact beneficial insects. These are troubling questions, and we don't know the answers yet."
About 15 million acres of Bt corn were planted the U.S. in 1998, which was just under 20% of the nation's total corn acreage.
The researchers grew Bt corn in a plant-growth room and then collected samples of root exudates from the roots and from nearby soil. They found that active Bt toxin was exuded by the roots throughout the growth of the plants, and that the toxin, which binds on soil, retained the ability to kill insect larvae. Previous studies with purified toxin showed that it retained insecticidal activity for 234 days, the longest time studied.
Guenther Stotzky is a professor of biology at New York University. He is the director of NYU's Laboratory of Microbial Ecology. He received his Ph.D. from The Ohio State University.
This research was funded by the United States Environmental Protection Agency.
Journal
Nature