Plant Biotech Blog

Transgenic technology, involving a wide range of pesticidal genes from the bacterium Bacillus thuringinesis (Bt), dominates the scenario of agricultural biotechnology. At the same time, Bt technology is also the most vehemently criticized area of agricultural biotechnology.

While the terms Bt cotton, Bt corn, Bt potato, etc., are widely used, the level of understanding of what the technology actually means, what it can and what it cannot do, is very poor. A variety of issues such as the biology of Bacillus thuringiensis, its toxins, use of Bt as a biopesticide, transgenic Bt crops, benefits and limitations of the technology and biosecurity, are important components of public awareness. This article is about the biology of Bt, its use as a conventional biopesticide, Bt toxins and the pre-requisites for their functioning.

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A new technology is developed either to improve an existing one or to fulfill the need for an inventive measure. Every technology comes with defined and realizable objectives, providing a practical solution to a problem. The public should be made aware of the realizable benefits of a new technology, evaluated realistically, against the background of science and its promise. Since most of the questions raised about genetically engineered (GE) products are related to science behind the technology, the answers should come from the same platform.

The consumers should be informed clearly both about the benefits and limitations of a technology and be assured that there is no more than an acceptable risk in adopting that technology and that the benefits outweigh the risks.

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Genetically engineered (GE) products are the most extensively tested for safety among all feed and foods and their safety has been well established. The livestock and people of the US are the living testimony for the safety of GE products. Not even a single case of toxicity from GE products was ever proved. Nevertheless, the issue of toxicity of GE feed and foods is a potent weapon in the armoury of anti-biotech activists.

Bacillus thuringiensis (Bt) proteins do not get into the cotton fibre, which is most used. Nor into the seed oil, but may be present in small quantities in the seed cake used as livestock feed. The critics often claimed that the levels of Bt protein in the Bt plants fall drastically so as to be ineffective against the bollworm, after such short periods as 100 days. Yet, when convenient, they also claim that the seed is toxic to all life.

The question of toxicity of GE products is raised in even very improbable, ridiculous and absurd situations. The latest is the report in the The Hindu (June 25, 2005), that “at least 12 peacocks died today after consuming Bt cotton seeds possibly in a field near Mamidalapalli village, about 80 km from here (Karimnagar),” Andhra Pradesh, India. (http://www.hindu.com/thehindu/holnus/004200506252101.htm).

The verdict is out even before the post-mortem was conducted to determine the cause of death of the birds. The report has no other details such as how the birds came to eat Bt cottonseeds or if someone fed them the seed. The peacocks could not have picked the seed from plants in the cotton field as it is not yet the fruiting season and last season’s cotton has already been marketed. Was feeding the birds a mischief or the reporting itself? Peacock is a protected and much romanticized National Bird of India and it is so easy to whip up strong emotions about it in the masses.

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Risk of allergy from genetically engineered (GE) foods has been made a major biosafety issue, based on two, but now defunct cases.

A gene for the Brazil nut protein was introduced into soybean to increase the content of methionine, an essential amino acid. The serum from people allergic to Brazil nuts cross-reacted with extracts of transgenic soybean and not with extracts of its isogenic. Though no one actually developed allergy by eating the transgenic soybean, since the transgenic is likely to affect people who are allergenic to Brazil nuts, Pioneer Hi-Bred International, the developer of the product, did not proceed with it, an example of self-regulation.

The Bt Cry9 protein in the Aventis Starlink Bt corn is more stable in simulated digestion than other Bt proteins, and so it was thought that it might be allergenic. The United States Department of Agriculture (USDA) cleared it for use as both food and feed, but the US Environment Protection Agency (EPA) took a precautionary measure and approved this corn only for animal feed, as animals do not generally suffer from food allergies. When subsequent studies have shown that Bt Cry9 protein is not allergenic, the EPA too cleared it as food. Bt Cry9 protein was never demonstrated to be allergenic. The US Centers for Disease Control (CDC) tested 17 alleged samples of blood from people claimed to have developed allergenic reactions to Starlink and found that none of the blood samples showed cross-reactivity to Cry9 Bt protein. The Cry9 gene is not deployed in any commercial product now. Since transgenic products approved as only feed may get into the food products, as has happened with Starlink Bt Cry9 corn that appeared in Taco Bell taco shells, no transgenic is now approved exclusively for use as feed. This shows that the regulatory regime is in fact functioning effectively.

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