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Why does bacillus thuringiensis produce bt toxin?

Why does bacillus thuringiensis produce bt toxin?


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Background : B.thuringiensis produces an inactive crystalline toxin during sporulation which when ingested by an insect, gets activated and causes pore formation in gut , subsequently leading to death of the insect.

Question : What is the role of the toxin in bacteria's own metabolism ? Does it "unintentionally" kill the insects or is there an evolutionary advantage gained by the bacteria ?


Bt-Corn: The Biggest GE Crop

Bacillus thuringiensis, or Bt, is a common soil bacterium whose genome contains genes for several proteins toxic to insects. For decades, Bt has been sprayed on fields as an organic pesticide several major pests of corn that are difficult and expensive to control with chemical insecticides are susceptible to Bt. When sprayed on the surface of crops, however, Bt toxins break down quickly when exposed to ultraviolet light, and they also wash off in a strong rain.

To address these problems, several varieties of corn have been genetically engineered to incorporate Bt genes encoding proteins called “delta-endotoxins” and “vegetative insecticidal proteins” (VIPs), which are specific to various insect pests. Some strains of Bt produce proteins that are selectively toxic to caterpillars, such as the southwestern corn borer, while others target mosquitoes, root worms, or beetles. To create a Bt crop variety, plant scientists select the gene for a particular Bt toxin and insert it into the cells of corn or cotton plant at the embryo stage. The resulting mature plant has the Bt gene in all its cells and expresses the insecticidal protein in its leaves. Caterpillars ingest the toxin, which fatally damages the lining of the gut.

Because Bt-corn produces an insecticide within its tissues, the toxic proteins are protected from the sun and thus persist longer. Moreover, Bt-corn makes the toxin continually over a season, extending its protective effects. Since Bt-corn offers an alternative to spraying chemical insecticides, it offers environmental and economic benefits to farmers. Most Bt toxins are selective for specific caterpillars and closely related species. There are no known effects to mammals, fish, or birds, and they appear safe for consumers. Nevertheless, future varieties that entail changes in plant metabolism could possibly be associated with toxicity. 1


Popular Questions of Class 12th biology

  • Q:- Why is reproduction essential for organisms? Answer
  • Q:- What is spermatogenesis? Briefly describe the process of spermatogenesis.
  • Q:- With a neat diagram explain the 7-celled, 8-nucleate nature of the female gametophyte.
  • Q:- With a neat, labelled diagram, describe the parts of a typical angiosperm ovule.
  • Q:- Differentiate between a zoospore and a zygote.
  • Q:- What is triple fusion? Where and how does it take place? Name the nuclei involved in triple fusion.
  • Q:- What is oogenesis? Give a brief account of oogenesis.
  • Q:- Write a short note on
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    (b) Adaptations of plants to water scarcity
    (c) Behavioural adaptations in animals
    (d) Importance of light to plants
    (e) Effect of temperature or water scarcity and the adaptations of animals.
  • Q:- Differentiate between microsporogenesis and megasporogenesis. Which type of cell division occurs during these events? Name the structures formed at the end of these two events.
  • Q:- Differentiate between the followings:
    (a) Repetitive DNA and Satellite DNA
    (b) mRNA and tRNA
    (c) Template strand and Coding strand

All about Bacillus thuringiensis

Bacillus thuringiensis (Bt) are bacteria found naturally in the environments of every continent of the world. Some of the Bt strains are natural antagonists of some pests. A few Bt strains have been selected and commercialized as biological pest control products. These commercialized Bt strains are valuable to agriculture and public health because of their unique ability to naturally control certain destructive and disease-carrying insect pests while avoiding harm to non-target organisms (such as beneficial insects, people, other mammals, and fish). Biological insect control products based on Bt strains have been used safely and effectively in practical field conditions for more than 50 years, since its first commercial use in France in 1938.

The increasing use of biological pest control is reflective of a greater need for sustainable crop protection solutions, that meet the demands of consumers for food and environmental safety. Bt insect pest management is vital to producers of food, fiber and timber and in public health protection around the globe. Bt-based products are used widely in organic and conventional agriculture as well as forestry and public health, because they deliver consistent pest control while avoiding harm to beneficial insects, without negative impacts on the environment or people. Bt is a sustainable crop protection solution when used as part of effective integrated pest management and insecticide resistance management programs.

Bt safety and effectiveness are vital to ensure a sustainable food production and control of diseases in public health programs.

Commercial insect control products, based on specific Bt strains, are eaten by target pest insects. This prevents them from digesting food, causing them to die. The component of commercial Bt products that affects pest insects is a group of naturally produced proteins that have evolved to impact only the target insect’s gut. For example: caterpillar control products based on Bt can only be activated in the caterpillar gut. This specificity is why they have little to no negative effects on non-target organisms such as other insects (e.g. pollinators like bees), animals, people, or fish.

People have been eating fresh food treated with commercial Bt products for more than 50 years without any evidence of adverse effects. Bt strains used in pest control have evolved to survive best in the specific condition of the pests they target. These conditions are so dramatically different from the human gut that Bt do not grow like they would in the targeted pest insects in the field.

Bacillus cereus (Bc) are members of the Bacillus bacteria family and found naturally in the environment. Some Bc strains produce certain toxins, like the emetic toxin and enterotoxins, which can be harmful to people. The emetic toxin is particularly of concern because it is not destroyed by cooking and causes vomiting. Although related to Bc it has been proven that commercial Bt strains do not have the ability to produce this toxin.

In addition to the emetic toxin, some Bc strains can produce large amounts of enterotoxins which can cause diarrhea. Research has shown that commercial Bt strains are unlikely to produce any of these toxins in the human digestive system.

Bacillus cereus (Bc) are natural, common ubiquitous soil bacteria, so it is not unlikely to find them in food. The types of Bc that are most likely to adversely affect people are found in meats and starchy processed foods. Fresh vegetables and fruits are highly unlikely sources of pathogenic Bc strains.

There is no evidence of a link between pathogenic Bc presence in food and the application of commercial Bt products. The Bt products do not contain pathogenic Bc.

Enterotoxins can only be produced when a microbe is actively growing. Commercial Bt strains have been shown to have little to no growth on fruits and vegetables or in the human digestive system.

Current methods to differentiate Bt products from potentially pathogenic Bacillus cereus (Bc) are generally based on the presence of insecticidal protein crystals or through whole genome sequencing.

Research organizations are developing new methods using PCR technology (a technology used to amplify unique segments of the genetic code of the bacteria) or other modern tools to make this easier and faster.

There is a need for methods to rapidly differentiate Bt from Bc in food. Bt is necessary for sustainable food production because of its positive worker-safety profile, low impact on the environment and compatibility with beneficial insects whereas Bc is not used in agriculture but is natural occurring.

IBMA is open to opportunities for collaboration to fulfill this pressing need.

Commercial Bt are produced through fermentation in controlled, clean, conditions in fermenters, similar to those used to produce beer. Beginning with highly purified cultures, conditions are carefully controlled to favor the growth of only one organism: B. thuringiensis. Because each bacterial strain can have slight variations in their optimal growth parameters, commercial Bt fermentation is carefully controlled to cover the specific needs of the single commercial strain being grown. Commercial Bt products must conform to strict international guidelines of the OECD for microbial contamination, which is stricter than food safety requirements in some cases. Commercial Bt strains themselves are identity-preserved through carefully maintained seed stock from the original isolates found in nature. This careful process makes sure it is the same pure strain every time a product is produced. Commercially produced Bt strains have been used effectively and safely for more than 50 years.

To ensure the safety and effectiveness of products used in agriculture, the European Union has the most extensive and strict pesticide regulations in the world. Producers of Bt must submit detailed dossiers that include specific studies on human, animal, and non-target insect toxicology, long- and short-term environmental impact, and detailed assessments of the microorganism, among other requirements. These dossiers and studies are reviewed by regulators in all member states and by the European Food Safety Authority before the Bt products can be registered for use. Bt products are currently registered in all European countries. Regulatory agencies around the world, including the World Health Organization, have confirmed the value and safety of Bt products. An outline of the extensive review process is available on the website of the European Food Safety Authority : https://www.efsa.europa.eu/en/interactive-pages/pesticides-authorisation/PesticidesAuthorisation

As with any crop protection product, Bt products should always be used according to label instructions, including the use of PPE.


Why does bacillus thuringiensis produce bt toxin? - Biology

Animal Safety

Bt products are found to be safe for use in the environment and with mammals. The EPA (environmental protection agency) has not found any human health hazards related to using Bt. In fact the EPA has found Bt safe enough that it has exempted Bt from food residue tolerances, groundwater restrictions, endangered species labeling and special review requirements. Bt is often used near lakes, rivers and dwellings, and has no known effect on wildlife such as mammals, birds, and fish.

Humans exposed orally to 1000 mg/day for 3-5 days of Bt have showed no ill effects. Many tests have been conducted on test animals using different types of exposures. The results of the tests showed that the use of Bt causes few if any negative effects. Bt does not persist in the digestive systems of mammals.

Bt is found to be an eye irritant on test rabbits. There is very slight irritation from inhalation in test animals which may be caused by the physical rather than the biological properties of the Bt formulation tested.

Bt has not been shown to have any chronic toxicity or any carcinogenic effects. There are also no indication that Bt causes reproductive effects or birth defects in mammals.

Bt breaks down readily in the environment. Because of this Bt poses no threat to groundwater. Bt also breaks down under the ultraviolet (UV) light of the sun.


Is Bt corn safe?

Considered safe to humans, mammals, and most insects, Bt has been a popular pesticidal spray since the 1960s because it had little chance of unintended effects. Engineering the gene into corn, however, caused an unexpected public backlash.

Likewise, what is Bt corn resistant to? Insect-resistant corn Bt corn is a variant of maize that has been genetically altered to express one or more proteins from the bacterium Bacillus thuringiensis including Delta endotoxins. The protein is poisonous to certain insect pests.

Simply so, is Bt corn classified as a pesticide?

Bacillus thuringiensis, or Bt, is a common soil bacterium whose genome contains genes for several proteins toxic to insects. For decades, Bt has been sprayed on fields as an organic pesticide several major pests of corn that are difficult and expensive to control with chemical insecticides are susceptible to Bt.

How does Bt corn affect the environment?

Bacillus thuringiensis (Bt) is a soil bacterium that produces insecticidal toxins. Genes from Bt can be inserted into crop plants to make them capable of producing an insecticidal toxin and therefore resistant to certain pests. There are no known adverse human health effects associated with Bt corn.


BT CORN: IS IT WORTH THE RISK?

Bt corn, a genetically modified organism (GMO), has been both the poster-child and thorn-in-the-side of the plant biotechnology industry from the late 1990’s to present. There are several versions of this transgenic crop that each have a gene from an insect pathogen, Bacillus thuringiensis (Bt), which encodes a protein toxic to the European corn borer (ECB), an insect pest that eats and destroys corn stems (see Figure 1). Bt corn has proven effective in reducing crop damage due to ECB, yet public opposition to Bt corn has escalated amid fears of human health and environmental risks associated with the production and consumption of Bt corn.


Figure 1. Engineering resistant corn. Following the insertion of a gene from the bacteria Bacillus thuringiensis, corn becomes resistant to corn borer infection. This allows farmers to use fewer insecticides

Bt corn draws its humble origins from France, where in 1938 B. thuringiensis bacteria was grown in large quantities and sprayed on corn crops to prevent ECB damage[1]. Artificial selection of Bt strains has led to the successful targeting of many insect pests. Because no toxic effects of Bt on humans have been detected in its seventy years of use, it is now considered an acceptable pest control measure for the organic food industry[2]. To this day, Bt is an important part of many integrated pest management strategies. The success of the Bt spray has been limited because the bacteria cannot survive for very long on the plant’s surface. Bt is particularly ineffective at controlling ECB because these insect live most of their larval life inside the corn stem, not on the surface: sprays are only effective when the insects are starting its journey into the stem. Thus, a means of penetrating corn tissue with Bt is required to offer long-term anti-feeding measures against tunneling insects such as ECB.

Mechanism of Bt toxicity

Researchers investigated how this bacteria kills particular insects and discovered that Bt has two classes of toxins cytolysins (Cyt) and crystal delta-endotoxins (Cry)[3]. While Cyt proteins are toxic towards the insect orders Coleoptera (beetles) and Diptera (flies), Cry proteins selectively target Lepidopterans (moths and butterflies). As a toxic mechanism, Cry proteins bind to specific receptors on the membranes of mid-gut (epithelial) cells resulting in rupture of those cells[4]. If a Cry protein cannot find a specific receptor on the epithelial cell to which it can bind, then the Cry protein is not toxic. Bt strains will have different complements of Cyt and Cry proteins, thus defining their host ranges[5]. The genes encoding many Cry proteins have been identified providing biotechnologists with the genetic building blocks to create GM crops that express a particular Cry protein in corn that is toxic to a particular pest such as ECB yet potential safe for human consumption.

As it turns out, nature has its own biotechnologist called Agrobacterium tumefaciens which induces the growth of tumours on woody plants. These tumours are engineered by A.tumefaciens to produce a special food for the bacteria (opines) that plants normally cannot make. These tumours arise from a unique bacterial transformation mechanism involving the Ti-plasmid which coordinates the random insertion of a subset of its DNA (t-DNA) containing opine synthase genes into a plant chromosome[6] (see Figure 2). By replacing portions of the t-DNA sequence with genes of interest (such as Cry), researchers have been able to harness this transformational mechanism and confer new traits to many flowering plants including grasses such as corn7 and rice[8]. Cry-transformed corn varieties, called ‘Bt corn’, produce sufficient levels of Cry proteins to provide an effective measure of resistance against ECB and are now widely grown in North America.


Figure 2. General schematic of GM crop production

Human health and environmental risks

The promise of this technology has been largely overshadowed by concerns about the unintended effects of Bt corn on human health and the environment. Cry protein toxicity, allergenicity, and lateral transfer of antibiotic-resistance marker genes to the microflora of our digestive system threaten to compromise human health. Despite these alarming possibilities, the risks to human health appear small based upon what is known about the bacterial endotoxin, its specificity, and confidence in the processes of plant transformation and screening[9]. The task of determining the levels of such risks, however, are immense. Human diets are complex and variable. How can we trace the acute or chronic effects of eating GM ingredients when they are mixed in with many other foods that may also present their own health hazards? It is even more complicated to determine the indirect risk of eating meat from animals raised on transgenic crops. These tests take time, and the results of clinical trials are not always clear-cut. It will likely take decades before we can know with any certainty if Bt corn is as safe for human consumption as its non-GM alternatives[10].

We currently know very little about the actual ecological risks posed by Bt corn. Bt corn may be toxic to non-target organisms, transgenic genes may escape to related corn species, and ECB and other pests may become resistant to Cry proteins[11]. The alleged effect of Bt corn pollen on Monarch butterfly larvae has rocketed to the front pages of major newspapers around the world (ex. CNN). Some research has shown that Monarch butterfly larvae fed their normal diet of milkweed leaves suffer a significant decline in fitness when those leaves are dusted with Bt corn pollen (Losey et al. 1999). The methodology of this experiment, however, has been harshly criticized by members of the scientific community.

Most recently, the threat of Cry gene escape into wild populations has been substantiated by the discovery that artificial DNA from transgenic corn has been detected in traditional corn varieties in remote areas of Mexico (Quist and Chapela, 2001). However, this study was pulled from NATURE magazine in an unprecedented fashion following a heated scientific and political debate[12]. While few contest that such transgenes are present in the local corn races of Mexico, there is still no evidence to suggest that these genetic constructs are “escaping” to become established in local corn races. We are limited to an educated guess as to the likelihood and speed of such genetic pollution[13].

Balancing risk and benefit

Despite the lack of conclusive evidence that GM foods present considerable risk to human health and environment, widespread use of this new technology is being compared to past mistakes such as broadcast spraying of populated towns with DDT to control mosquitoes during the 1950s. Notions of “frankenfoods”[14] and “agroterrorism”[15] corrupting our planet present theoretical possibilities that cannot be discounted given the remarkable ability of the unlikely to become an actuality. In truth, we must plead ignorance of the long-term impacts of GM crops[16].

Arguably, every food in our current diet carries with it associated risks, determined through “trial-and-error” extending back before to our hunter-gatherer origins. Often, we will accept a certain degree of exposure to known hazards to receive known benefits. Bt corn has obvious benefits for agricultural production, increasing profit margins through more efficient and consistent corn production and improving the working environment for farmers through reduced exposure to pesticides. In a surplus market, these benefits may be passed on to the consumer as a grocery bill reduction. On a global scale, decreased crop losses due to herbivory may translate into improved world food supply since corn remains a major staple in the global diet. Ecosystems are not likely to benefit from ECB-resistant Bt corn propagation since this technology replaces a largely mechanical (non-chemical) control for ECB.

These benefits, real or imagined, have been used as leverage by Bt corn proponents in the argument to accept what they argue are minimal levels of health and environmental risk. Yet many consumer, civil rights, and environmental advocacy groups characterize such arguments as industry propaganda, asserting that corporate benefits should not out-weigh the undetermined human health, socioeconomic and environmental risks.

The relative ease in engineering Bt biopesticides into crops such as corn, cotton and rice, combined with the cost effectiveness of Bt crops for growers under threat of ECB, makes banning this technology in North America seem unlikely. This reality highlights the necessity for the research community to improve methods for assessing risks posed by GM crops. While some industry proponents may resist, it is ultimately the public’s responsibility to ensure that this new technology is properly managed in the context of other pest management methods that have their own set of risks and benefits.

Artificial Selection – the encouragement of certain traits in an animal through selective breeding by humans, both intentional or unintentional

Ti plasmid – “tumour-inducing” plasmid: originally found in the bacterium Agrobacterium tumefaciens, this plasmid integrates into a host cell genome and causes galls on plants. Biotechnologists can take advantage of this integration to insert genes of their choice into plant cells.

Lateral transfer – also called horizontal gene transfer, the movement of genetic material from one organism to another other than from parent to offspring, and often across species, genus, or even domain.

Antibiotic resistance marker genes – genes that allow biotechnologists to distinguish between plants that have been modified properly and those that have not depending on their suceptibility to antibiotics.

Screening – the process of selection of desirable plants from a large population of transformants (different insertional events) with variation in trait depending on location and number of t-DNA insertions.

Herbivory – the consumption of plants by animals, in this case to the detriment of the plant (predation).

1. Van Frankenhuyzen, K. in Bacillus thuringiensis, An environmental biopesticide: Theory and practice (John Wiley & Sons, 1993).

2. Whalon, M.E. & Wingerd, B.A. Bt: mode of action and use. Arch Insect Biochem Physiol 54, 200-211 (2003).

3. Crickmore, N. et al. Revision of the nomenclature for the Bacillus thuringiensis pesticidal crystal proteins. Microbiol Mol Biol Rev 62, 807-813 (1998).

4. Dorsch, J.A. et al. Cry1a Toxins of Bacillus Thuringiensis Bind Specifically to a Region Adjacent to the Membrane-Proximal Extracellular Domain of Bt-R-1 in Manduca Sexta: Involvement of a Cadherin in the Entomopathogenicity of Bacillus Thuringiensis. Insect Biochemistry and Molecular Biology 32, 1025-1036 (2002).

5. De Maagd, R.A., Bravo, A. & Crickmore, N. How Bacillus Thuringiensis Has Evolved Specific Toxins to Colonize the Insect World. Trends in Genetics 17, 193-199 (2001).

6. Bevan, M.W. & Chilton, M.D. T-DNA of the Agrobacterium Ti and Ri plasmids. Annu Rev Genet 16, 357-384 (1982).

7. Ishida, Y. et al. High efficiency transformation of maize (Zea mays L.) mediated by Agrobacterium tumefaciens. Nat Biotechnol 14, 745-750 (1996).

8. High, S.M., Cohen, M.B., Shu, Q.Y. & Altosaar, I. Achieving successful deployment of Bt rice. Trends Plant Sci 9, 286-292 (2004).

9. Kuiper, H.A., Kleter, G.A., Noteborn, H.P. & Kok, E.J. Assessment of the food safety issues related to genetically modified foods. Plant J 27, 503-528 (2001).

10. Sudakin, D.L. Biopesticides. Toxicol Rev 22, 83-90 (2003).

11. Sharma, H.C. & Ortiz, R. Transgenics, Pest Management, and the Environment. Current Science 79, 421-437 (2000).

12. Ochert, A. Caught in the maize at Berkeley. California Monthly (2002).

13. Letourneau, D.K., Robinson, G.S. & Hagen, J.A. Bt crops: predicting effects of escaped transgenes on the fitness of wild plants and their herbivores. Environ Biosafety Res 2, 219-246 (2003).

14. Golden, F. Who’s afraid of Frankenfood? Time 154, 49-50 (1999).

15. van Bredow, J. et al. Agroterrorism. Agricultural infrastructure vulnerability. Ann N Y Acad Sci 894, 168-180 (1999).

16. Hoffmann-Riem, H. & Wynne, B. In risk assessment, one has to admit ignorance. Nature 416, 123 (2002).


Toxic crops

La gran parte delle colture geneticamente modificate rientrano in due tipi di categorie. Vi sono quelle pensate per resistere all’alta tossicità degli input chimici tipici dell’agricoltura industriale, e poi vi sono quelle colture capaci di produrre da se stesse queste sostanze. Il primo gruppo di colture GM sono state pensate per resistere a degli specifici erbicidi come il glifosato (Roundup) o il glufosinate (Liberty), capaci di uccidere tutte le altre erbe intorno il secondo gruppo è composto da quelle colture che sono in grado di produrre un pesticida tossico per gli insetti che provano ad alimentarsi su quella pianta.

Herbicide resistant (HR) crops

GM herbicide-resistant crops have been grown commercially since the mid-1990s, mostly in North and South America. Cultivating herbicide-resistant crops promotes, and significantly increases, the use of chemical herbicides, such as Monsanto’s ‘Roundup’ and Bayer's 'Liberty'.

However, over time, weeds develop resistances to the herbicides, which leads to the use of even more herbicides that are even more toxic.

This forces farmers onto an endless chemical treadmill. Weed resistance continues to increase, US farmers reported that on half of their land weeds are resistant to Roundup and that is spreading faster each year. Fields covered with resistant weeds increased by 25% in 2011 and 51% in 2012.

Pesticide producing crops (Bt)

‘Bt’ crops are genetically modified to produce an insecticide bacillus thuringiensis protein that is toxic for pests feeding on them. Bt crops produce this toxin in their leaves, roots and stems, killing insects like the European corn borer or rootworm borer. However, the toxin can also be damaging for other insects such as butterflies and moths, and the insect pollinators that conventional farmers rely upon.

Monsanto’s Bt maize, called MON810, is the only GM-crop grown on a considerable scale in the EU, namely in Spain and Portugal. In Spain, contamination of organic maize crops by GM maize has caused severe hardship for organic farmers. MON810 has been banned in Austria, France, Germany, Greece, Hungary, Luxembourg and Poland.

There is still little known about how Bt plants interact with the environment. Very little research has been published about the various Bt toxins in GM maize plants and their potential effects on bees and other pollinators, and the impacts on soil ecosystems and organisms like earthworms or arthropods.

For the official approval of Monsanto’s Bt maize, the impacts upon butterflies and moths are predicted using overly simplistic models that don’t reflect the reality of farming methods and ecosystems in Europe, and the negative impacts are down-played.

To compound the unknown dangers, Bt crops are also constantly producing the toxin. While insecticides were traditionally sprayed at specific times to reduce insect populations, the Bt toxin is produced over many growing seasons and in all weather conditions – so that it is needlessly released even in years and periods where there is no pest threat. This contradicts the aim of current EU pesticide law that states that any kind of pesticide should only be used if the actual damage to crop yield from pests is significant.

The Bt approach to pest management is now considered a failure. In the US, reports state that Bt crops no longer provide protection against the very corn borers they were designed to resist.

Alternative solutions

The GM model of farming is unsustainable and damaging to the environment and rural communities. The increase in herbicides significantly increases pollution and health risks for citizens, and contributes to the loss of biodiversity. It is also entraps farmers who suffer greater cultivation costs and more dangerous working environments. In the meantime, profits from the sale of herbicide-resistant crops benefit large chemical manufacturers and agribusinesses.

In short, both herbicide resistant and pesticide producing GM-crops are unwanted and unnecessary. There are currently no herbicide-resistant crops authorised for cultivation in Europe, and in several European regions, neither European corn borer nor rootworm borers cause any significant economic damage for farmers.

Experts agree: the most effective protection against the buildup of weeds and pests such as rootworm is to rotate crops and avoid monocultures where the same crop is planted year on year. Further protection against the corn borer is afforded by chopping the harvest left-overs and mixing them with the soil. Organic and conventional methods of pest prevention work – so why do we need GM?


Why does bacillus thuringiensis produce bt toxin? - Biology

Few technologies have been demonized to the same extent as genetic engineering. According to countless websites, GMOs are an evil scourge on the earth that destroy biodiversity, use exorbitant levels of pesticides, and hybridize rampantly with wild crops, and all of that is before we even get to the (largely false) claims about Monsanto. Reality, however, shows a rather different picture, especially when it comes to Bt GMOs, which are what I want to focus on for this post. You see, one of the problems with GMO debates is that people on both sides tend to lump all GMOs together, but there are actually lots of different types of GMOs with different properties and different pros and cons. Of these different types, Bt GMOs are arguably one of the best, and as I will show, they actually reduce pesticide use, increase crop yields (thus reducing land use), increase profits for farmers, and are safer for the environment than their conventional counterparts (including organic farming). Further, they actually benefit farmers who don’t grow GMOs by providing a protective “halo” around their farms that protect them from insect pests. As a result, non-GMO farms that are near Bt GMO farms actually use less pesticides and enjoy higher profits than they would without the GMO farms.

Note: Many Bt GMOs are not herbicide resistant (i.e., aren’t designed for use with glyphosate [aka roundup]), so if your issue with GMOs is that you don’t like glyphosate, you should be fine with many Bt GMO crops (also you should read the actual scientific literature on glyphosate).

Bt pesticides and Bt GMOs

Before we can talk about the benefits of Bt GMOs, we need to talk about the alternatives and history of Bt. Bt toxin is actually a crystalline protein produced by the bacteria Bacillus thuringiensis, and decades ago, scientists discovered that it was a very effective pesticide against certain groups of insects, while being safe for most other organisms. There are three reasons for this. First, the acidic stomachs of mammals (and many other animals) degrades the protein. Second, only part of the protein is potentially dangerous, and it has to be broken down in a highly alkaline environment (which is present in insect guts, but not most animals) to release the potentially dangerous part. Third, it operates by binding to specific receptors that are found on certain insect guts, but not the guts of other animals. Thus, its mode of action simply doesn’t work on humans and most other animals (for more details about mode of action, see Kumar and Chandra 2008 and this page from Harvard). As a result, it is safe for humans and most animals at anything but an extremely high dose (Mendelsohn et al. 2003 remember, even water is fatally toxic at a high dose [Garigan and Ristedt 1999]).

All of these properties make Bt toxin an ideal pesticide, and it was widely adopted, particularly for organic farming (yes, organic farming uses pesticides as well, just not “synthetic” pesticides). As far as pesticides go, it is a pretty safe one, but it is still not without problems. First, the spraying process takes time and money, uses water, burns fossil fuels, has to be done multiple times a year, etc. Additionally, when it is sprayed on crops, it kills a wide range of insects that were on the crops, not just the ones that actually eat the crops. Further, spraying has to be timed correctly, it doesn’t provide continuous protection, etc. Also, it is far from the only insecticide being used, and many are far worse for the environment. This is where GMOs come in.

Clever scientists figured out a way to genetically engineer plants to produce Bt toxin themselves. As a result, minimal spraying is needed, because the plant produces its own pesticide (keep in mind, this pesticide is very safe for humans). This saves farmers time and money, provides continuous protection (resulting in higher crop yields), and has fewer effects on non-target species. I’ll elaborate on all of these points below.

Note: Pesticides are simply chemicals used to kill pest species. Insecticides, herbicides, fungicides, etc. are all types of pesticides that target specific groups (insects, plants, and fungi, respectively).

Reduced pests, reduced pesticides, increased yields, and increased profits

I sometimes hear those who oppose GMOs claim that GMOs haven’t delivered on their promises, but when it comes to Bt GMOs (as well as most other GMOs), that is demonstrably false. Numerous studies have consistently confirmed that Bt GMOs greatly reduce pest populations, which results in less damage to the crops (Hutchison et al. 2010 Lu and Desneux 2012 Dively et al. 2018). Further, all of this is accomplished while using less pesticides (Shelton et al. 2002 Cattaneo 2006 Lu and Desneux 2012). This, of course, also translates to higher yields and higher profits for farmers (Shelton et al. 2002 Cattaneo 2006 Vitale et al. 2010). Indeed, one study estimated that over a 14 year period, Bt maize (aka corn) saved farmers in Illinois, Minnesota, and Wisconsin $3.2 billion, and saved farmers in Iowa and Nebraska $3.6 billion (Hutchison et al. 2010). So, don’t believe the anti-GMO horror story that GMOs are somehow bad for farmers. They aren’t. Farmers choose to use them because they benefit the farmers.

Note: The studies cited in this post came from a wide range of countries, not just developing countries. Australia, the USA, China, European countries, and African countries are all represented in the studies I cited throughout.

Environmental benefits

As explained in the previous section, Bt GMOs use significantly less pesticides than their conventional/organic counterparts. That reduction stems from the fact that non-GMO crops are frequently sprayed with insecticides whereas the Bt GMOs produce their own insecticides, which greatly reduces the need for spraying pesticides. So, if your biggest concern with GMOs is that they use too many pesticides, then you should support Bt GMOs, because they use substantially less than other agriculture methods (including organic).

Because of the targeted nature of GMOs, this reduction in pesticide use translates directly to improved biodiversity, while still effectively killing pests. When a field is sprayed with an insecticide (even a fairly safe one like the Bt spray used in organic farming), a large range of insects in the field are affected, even if they aren’t pest species. In other words, things like bees and monarch butterflies (particularly their caterpillars) can be killed by the pesticide, even though they aren’t pest species and don’t eat the crops (depending on the pesticide, there can also be negative effects for other wildlife, aquatic ecosystems, etc). This is inevitable collateral damage from spraying pesticides. The Bt GMOs, however, are very targeted. Insects need to actually eat the plant to get the toxin. As a result, innocent, non-pest species that just happen to be in the field are largely unaffected. Plus, there are no pesticides running into waterways and the other negative effects of pesticides are eliminated.

To be clear, this isn’t speculative, dozens of studies have confirmed this. Indeed, several meta-analyses of the literature have found that Bt GMOs do not adversely affect non-target species, and, compared to crops that are sprayed with Bt, they have significantly better insect diversity (Marvier et al. 2007 Wolfenbarger et al. 2008 Comas et al. 2014). Additionally, one study found that by reducing the use of pesticides, Bt GMOs actually increased populations of insect predators, such as birds (Lu and Desneux 2012). So, if your concern with GMOs is biodiversity, then, once again, you should be supporting Bt GMOs, because they are demonstrably better than the alternatives.

Having said that, there are reports of some non-target insects being affected by Bt GMOs, but these are usually insects that specialize on eating or parasitising pest species (Wolfenbarger et al. 2008). So, in many cases, it’s not that the GMO itself harms them, but rather that the GMO kills their prey. Also, to be 100% clear, studies comparing Bt GMOs to conventional crops that are not sprayed at all have found that there is a slight difference in diversity levels (likely at least partially from the type of ecological interactions I just described Whitehouse et al. 2005), but the expectation that most crops shouldn’t be sprayed at all is unrealistic (it is a nirvana fallacy) and would result in other environmental problems (e.g., increased land area, tilling methods that damage the soil, etc.).

It’s also worth explicitly stating that the safety of Bt GMOs still holds true even if we look at specific groups that people care greatly about, like bees and butterflies. There was initial concern that the pollen from Bt crops could adversely affect these groups, but that suggestion was based on unrealistic exposure levels, it ignored the fact that they are affected by sprays, and subsequent studies have failed to find evidence that these crops harm bees (Duan et al. 2008) and non-pest butterflies (Mendelsohn et al. 2003). Further, Bt GMOs have one final benefit: reduced habitat loss.

Habitat loss and fragmentation is the single biggest threat to biodiversity (Newbold et al. 2015 Wilson et al. 2016 Young et al. 2016). Further, conversion of natural lands to agriculture is the biggest cause of habitat loss (Foley et al. 2005 Phalan et al. 2016) and is well known to be a serious threat to conservation (Martinuzzi et al. 2015 Tilman et al. 2017). This is one of the key reasons why, as a conservation biologist, I support GMOs. They have a higher yield than conventional crops, which means that they need less land to grow the same amount of food. Therefore, from an environmental standpoint, they are tremendously beneficial. Indeed, increasing crop yields is often argued as a key strategy for preserving biodiversity (Phalan et al. 2016 Tilman et al. 2017).

Let me try to explain it this way. All agriculture is bad for biodiversity. When you take a natural forest or grassland, clear it, and plant crops, you will inevitably lose a large number of species that used to live there. People often seem to have this idyllic view of farms (particularly organic farms) as if all the animals and plants that lived in the forest before it was cleared will somehow continue to live in the organic farm field. This is a fairy tale. Even if you rotate your crops, never till the soil, and never use any pesticides, the biodiversity of that farm field will still be substantially lower than what it was before you turned it into a farm field, because the field doesn’t contain the various habitat types that many animals need (e.g., a forest species is not going to live in a field). People seem to have no trouble realizing this when it comes to things like clearing rainforests to grow palm oil, but for some reason, when it comes to crops in countries like the USA and European countries, people suddenly don’t seem to realize how harmful clearing land for agriculture actually is, but its negative effects on biodiversity are well-documented (Krauss et al. 2010 Martinuzzi et al. 2015). As a result, methods that increase yield (thus reducing land use) are extremely beneficial for conservation.

Benefits to non-GMO farmers

If you listen to the anti-GMO crowd, they often operate under the pretense of protecting farmers who don’t grow GMOs, but as usual, reality is quite different. Indeed, several studies have confirmed that non-GMO farmers benefit tremendously from having Bt GMO farms near them. This is the case because the Bt GMO farms protect the non-GMO farms via what has been called the “halo effect.” You see, the Bt GMOs do such a good job of killing pest species, that the populations for those species decline in the areas where Bt GMOs are grown (Carrière 2003 Wu et al. 2008 Dively et al. 2018). Additionally, as mentioned earlier, Bt GMOs result in increased populations of generalist predators (such as birds) compared to non-GMO crops, and these predators act as biological control agents on the fields in their area (Lu and Desneux 2012). As a result of both of these factors, in the areas around Bt GMO farms, there are fewer pest insects to attack the non-GMO crops, and non-GMO farmers enjoy less crop damage, higher yields, and higher profits than they would if there were no GMO farms around (Hutchison et al. 2010 Wan et al. 2012 Dively et al. 2018). Remember that study that I mentioned earlier that found that Bt corn saved farmers billions of dollars? In Illinois, Minnesota, and Wisconsin $2.4 billion of those savings were by non-GMO farmers, and in Iowa and Nebraska $1.9 billion were by non-GMO farmers. Further, this protective halo effect allows non-GMO farmers to use fewer pesticide applications than they would need to otherwise (Wu et al. 2008 Hutchison et al. 2010 Dively et al. 2018). So, both the environmental and economic benefits of Bt GMOs spill over into the non-GMO farms.

Benefits to human health

In addition to the benefits to the environment and farmers, Bt GMOs have also been demonstrated to be safer for humans because of reduced mycotoxins (Pellegrino et al. 2018). These are chemicals produced by fungi, and can end up in our food when fungi are growing on the crops. The Bt crops don’t actually kill the fungi, but they do kill the pest-insects that make habitats for the fungi. You see, the fungi like to grow in the holes created by pest insects chewing on the plants. So, fewer pest insects means fewer holes, which means less fungi and less mycotoxins (Pellegrino et al. 2018). I don’t want to oversell this, because, at least in first world countries, food is usually checked for mycotoxin contamination, so food with it usually gets thrown out. Nevertheless, the filtering process is not 100% effective, and they are still a concern. So, the Bt GMOs do in fact reduce your risk of this (also, they reduce food waste, by reducing the amount of infected crops that get thrown out).

What about pesticide resistance?

At this point, people usually bring up pesticide resistance. This is the evolved resistance to Bt toxin that ultimately causes Bt to be ineffective at controlling insect populations (it is analogous to antibiotic resistance). This certainly is a problem, but it is not a problem that is limited to GMOs. Indeed, insects were documented evolving resistance to Bt long before GMOs were available (remember, Bt is used as a spray in many non-GMO farms, including organic farms McGaughey 1985 Tabashnik et al. 1990). So even if all the Bt GMO fields were replaced with organic fields (as some would like to see happen) we would still be having this problem because resistance to a widely used pesticide is an inevitable outcome of natural selection (at least inevitable without careful management).

The second problem with this argument is that resistance to Bt simply means that we can’t use Bt anymore. So, saying that we shouldn’t use Bt because it will create Bt resistant insects makes absolutely no sense. It is literally saying, “we shouldn’t use Bt, because if we use Bt we won’t be able to use Bt.”

Third, although resistance is a problem, it is not an insurmountable one. One current strategy that is widely used is to have “refuge” fields that are not Bt GMOs and are not treated with Bt (Siegfried and Hellmich 2012). Indeed, in the USA, the EPA requires farmers who use Bt corn to have at least 20% of their fields as refuge fields. This is a good strategy because of how natural selection works. I don’t want to get too bogged down in the details here, but in short, Bt GMOs (or Bt sprays) kill the majority of pest insects in the field, and only a handful that have alleles that are resistant to Bt will survive. If those insects mate with each other, we will quickly get a resistant population where all the insects have resistant alleles. By having a nearby refuge, however, we have a large population that is not resistant, making it more likely that the resistant insects will mate with the non-resistant insects, and the alleles for being resistant will be diluted. Indeed, it is well known that gene flow can swamp adaptation in this way (Kawecki and Ebert 2004 Foster et al. 2007 Funk et al. 2012 read this series for more about how evolutionary mechanisms work). Other strategies are also being developed and tested, so this is very much a situation where we should take the necessary precautions to prevent insect resistant, but there is no reason to use insect resistance as a general argument against the crops. As the old saying goes, don’t throw the baby out with the bathwater.

In short, Bt GMOs have tremendous benefits and are actually the opposite of most anti-GMO claims. For example, GMO opponents claim that GMOs increase pesticide use, but Bt GMOs greatly reduce it. Similarly, you may have heard the claim that GMOs are bad for biodiversity, but Bt GMOs are actually far better for it than non-GMO crops (including organic crops) because they are more targeted and have fewer effects on non-target species. Further, habitat loss is the dominant threat to biodiversity, but because Bt GMOs increase yields, they reduce the need for clearing habitat for agriculture. Additionally, they benefit farmers by increasing yields and profits, and they even benefit non-GMO farmers by providing a protective “halo” that increases the non-GMO farmers’ yields and profits and reduces their need for pesticides. So, from both an environmental and economic standpoint, Bt GMOs are better than the conventional and organic alternatives.


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Watch the video: Mechanism of action of Bt-toxin (May 2022).