Revolutionary Bt crops: Airing out the safety of a robust technology
AgriTechnology Plant Biotechnology

Revolutionary Bt crops: Airing out the safety of a robust technology

From the previous articles  of this series, hope the wrongly interpreted myths about genetically modified organisms (GMOs) have vanished once for you. We logically walked you through convincing evidences to prove GMOs are produced by mimicking naturally occurring processes for the welfare of human race and not unnatural or unethical. In the current issue we try to open your mind to clear ambiguities regarding the safety of another significant revolutionary technology of using Bt (Bacillus thuringiensis) genes for crop improvement.

In the present scenario, no one could have escaped from unanimous threats spread by different groups of people in popular magazines, social networks, etc., about the cultivation of Bt crops/ food products produced from Bt crops. All such falsely interpreted information has no scientific basis or evidence, taking advantage that no popular article (in blogs or newspaper) reader will asks for proofs. So it becomes easy to spread any such rumors to common public for their own popularity. In fact, we are here to break such non-scientific gossips and give you all readers about the actual truth behind Bt technology. So please make your mind neutral and continue reading to get the exact essence of information what is being interpreted here.

As we discussed in our previous article, in 1901, scientists identified a soil bacterium Bacillus thuringiensis which had an effective insecticidal activity against major crop pests. Farmers used the liquid formulation of this bacterium for several years to protect their crops from herbivorous insects. Actually insect killing properties of Bt was recognized several thousand years ago with evidence suggesting that Bt application may have already been in use in ancient Egypt. Moreover it is approved for use in ‘organic agriculture’ as it is a natural product (FAO guidelines on organic agriculture, 2001).  The major disadvantages of topical Bt pesticides are their shorter time of effectiveness and failure to persist in the target plants in changing environmental conditions (inactivation by UV light, heat, extreme pH, etc.). To overcome these problems, during 1980s, the advancement in molecular techniques enabled scientists to isolate the gene (popularly called Bt gene or cry gene) responsible for such insecticidal activity and transferred to several important crop plants to achieve built-in protection against insect pests. But most common question from the general public is that, if a Bt protein has an ability to kill an insect then what happens if the Bt foods are consumed by human or animals? Will it also kill us? Actually no. To know exact reason behind this specificity of Bt targeting insects, let us know about the mode of action of insecticidal Bt proteins.

How Bt protein kills insects?

Bt bacterium contains cry genes in its plasmid DNA coding for crystalline proteins during sporulation (a growth stage in spore forming bacteria) which has specific toxicity and kills target insects with higher specificity. It thrives mostly in soil and in some plant foliages. On eaten by an insect, crystalline protoxin (the precursor or inactive form) gets dissolved, digested and converts into an active toxin. The term ‘Bt toxin’ is used to imply its toxic ability against insects, but it is chemically a protein molecule with insecticidal activity. This Bt toxin (like a key) bind to the specific receptor (like a lock) in insect midgut epithelial cells and forms pores. This leads to ionic imbalance as a consequence of leakage through pores and ultimately causes death of an insect (due to inability to digest the food and starvation). Dead insects will provide nutrients for the growing bacteria. Scientists have identified several types of cry genes from various Bt strains and classified them in different groups based on its target insect groups and nucleotide sequence. For example Cry1 toxin target only lepidopteran insects (caterpillars) whereas Cry2 toxins target both lepidopteran and dipteran (flies) insects. Based on nucleotide sequence variation, it was further classified as Cry1Ac or Cry2Ab and so on. Diversity of Bt genes are still enormous. You can find entire Bt toxin list in Bt nomenclature database ( developed by Dr. Neil Crickmore. Utilizing these insecticidal cry genes and other insecticidal Bt genes, transgenic Bt crops have been developed and reaping benefits by its successful commercialization.  

‘Bt’ has high level of specificity to kill only target insects. It is safe to humans and animals
‘Bt’ has high level of specificity to kill only target insects. It is safe to humans and animals

Bt is safe for humans and animals

From the above discussion you could have understood about the exciting mechanism of Bt toxins. As described, Bt proteins need specific receptor molecule (which is also a protein) in the insect midgut to perform its insecticidal function. We humans and other animals, birds lack such receptors in the digestive system. So the ingested Bt toxin will get easily digested by our digestive enzymes like any other protein we eat. Moreover Bt toxins require alkaline pH (as in insects) to exhibit its toxic activity whereas animal digestive system including humans is acidic in nature. So it is highly unlikely that Bt proteins will be toxic to other organisms. From its introduction in 1996, Bt crops are being cultivated in several countries and they have been used as food and feed for several years. Though certain countries in European Union have prohibited the commercialization of Bt crops, they still continue importing the Bt products for food and feed purpose. Before commercializing any Bt or genetically modified crops all the biosafety trials are being conducted in a stringent manner. Few studies include acute oral toxicity of transgenic seed in rat, Primary Skin Irritation test in rabbits, Allergenicity studies, Feeding studies in lactating crossbred cows, Pollen flow studies, etc. Say for example in the toxicity study, the laboratory animals (rat, mice, guinea pigs, etc.) will be fed with Bt protein under study 1000 times higher concentration than the actual concentration produced in the plant. Such studies will completely ensure the safety of Bt food crops. Many supporting studies have been carried out by several scientific groups to generate biosafety data of Bt protein for food and feed purpose. Till date no scientifically proven or acceptable reports are available claiming that Bt foods are unsafe for human or animal consumption.       

Bt is safe for environment

Environmentalists constantly claim that pollen from the Bt crops will have ill-effect against the honey bees population. As we mentioned earlier, Bt toxins has higher specificity within the insect orders (categories of insects). Most of the beneficial insects like honey bees belong to an insect order Hymenoptera. Till date no Bt crops were commercialized to target insects belonging to this order. All the commercialized Bt crops were targeted against the insect pests belonging to the order Lepidoptera and Coleoptera. But still to convince the environmentalists and public, several studies (Study on beneficial fauna) have been carried out by the different scientists to prove Bt proteins in cultivated Bt crops doesn’t have lethal effect against honey bees population. On the other hand, the major objective of Bt crops are to reduce the damage caused by insect pests which ultimately require no or minimal insecticidal sprays. During the last 20 years with the adoption of Bt crops, the use of chemical insecticides were reduced by 50%, thereby reducing the detrimental effects on environment. In addition, farmers exposure to insecticides is also avoided and so we can claim that Bt crops have contributed more to safer ‘eco-friendly’ sustainable agriculture.                       

Impact of Bt crops on economy

Bt cotton and maize offer significant benefits all over the world. About 90% of farmers cultivating GM crops are resource poor farmers from developing countries. In china, economic gains at the farmer level from Bt cotton was US$17.5 billion for the period 1997 to 2014 and US$1.3 billion for 2014 alone. Since introduction of Bt cotton from 2002, India developed into a cotton exporter from an importer and became the top cotton producer in the world with 11.6 million hectares planted by 7.7 million farmers with an adoption rate of 95%. In other words only 5% of cotton cultivated in India is non-Bt cotton. India’s farm income from Bt cotton has enhanced by US$18.3 billion (about 1 lakh crores in Indian currency) between 2002 and 2014 and US$1.6 billion (about 10,000 crores) in 2014 alone. These reports indicate the impact of Bt crops on improving the livelihood of farmers. Recently, Punjab Agricultural university scientist has notified that the supply of Bt cotton varieties will be available soon to the farmers which could further cut down the cost of purchasing Bt cotton seeds in each cropping season. Bt brinjal has already shown its success in improving income of small-scale farmers of Bangladesh within a shorter period of its commercialization (2014-2016 – ISAAA 2016).

‘Bt’ as a natural gift to agriculture playing a phenomenal role in improving the livelihood of farmers cultivating Bt transgenic crops all over the world. Countries like India could further reap the benefit of it by permitting the cultivation of other Bt versions of major crop species.

However, it essentially needs strong public understanding and acceptance of this technology for sustainable intensification of crop productivity. Hope we justified the safety point of view on Bt technology. We kindly request the readers to spread the same to your family and friends in a way to support the efforts of global agriculturalists and let farmers to feed about 9.7 billion people in 2050 through successful adaptation of GM technologies.


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– (By Ram Sankar. C, Godwin James, Nandha Kumar. S and Ragavendran Abbai. Biotechnology graduates currently pursuing Post graduate in their field.)

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