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THE FAILURE OF Bacillus thuringiensis BIOTECHNOLOGY: A REVIEW


Afolabi Olubunmi
Benjamin Carson School of Medicine, Department of Biochemistry. Babcock University, Ogun State Nigeria

ABSTRACT

There is a new resolve, provoked by recent hikes in food prices around the world, to increase global food production in order to feed a rapidly growing population. In response to this, the biotechnology industry has made optimistic claims about the ability of genetically engineered (GE) crops—in which the plant DNA is changed using spliced genes that are often from unrelated organisms—to substantially increase farmers’ yields. Agricultural biotechnology has shown to increase crop production by seven- to tenfold in some developing countries, far beyond the production capabilities of traditional agriculture. Agricultural biotechnology is moving beyond input traits and is focused on delivering consumer health benefits. Over 10 new soybean varieties with human health benefits moving toward commercialization.

Bacillus thuringiensis (Bt) is a sporulating, Gram-positive facultative-aerobic soil bacterium. The spores contain crystals, predominantly comprising one or more Cry and ⁄ or Cyt proteins (also known as d-endotoxins) that have potent and specific insecticidal activity.  Bt toxins have been used as topical pesticides to protect crops, and more recently the proteins have been expressed in transgenic plants to confer inherent pest resistance. While some scientists have argued that Bt transgenic crops produced tremendous results upon their deployment, others have shown disappointment over the likely development of pest resistant insect strains. The aim of this present review attempts to focus on the failure of Bacillus thuringiensis biotechnology in the light of the usefulness of biotechnology.

Key words: Bacillus thuringiensis (Bt), Biotechnology, Pest, Resistance.

INTRODUCTION

Biotechnology has the power to increase human health, environmental sustainability and the wellbeing of consumers and farm communities globally. For example, higher yielding crops developed through agricultural biotechnology can contribute toward meeting the United Nation’s estimated need for a 50 percent increase in world food production by 2030. Biotechnology holds great promise for increasing the world’s food supply and improving the quality of that food. It is estimated that 800 million people around the world suffer from chronic food shortages, and millions more could go hungry due to current and future food crises.

Crops improved through biotechnology are producing higher yields worldwide to help feed a hungry and growing world. In 2007, 12 million farmers in 23 countries – 12 developing and 11 industrialized – planted 252 million acres of biotech crops, primarily soybeans, corn, cotton and canola. Eleven millions of these were small or resource-poor farmers in developing countries. Farmers earn higher incomes in every country where biotech crops are grown. When farmers benefit, their communities benefit as well 1.

Similarly, Biotechnology has a positive Impact on Human Health. Beneficial traits include lower saturated fat, increased omega-3 fatty acids and increased is flavone content. Consumers can rest assured that agricultural biotechnology is safe. These crops have been repeatedly studied and declared safe by expert panels the world over. In the 12+ years that biotech crops have been commercially grown, there has not been a single documented case of an ecosystem disrupted or a person made ill by these foods 2.

Despite the usefulness and the great promises biotechnology offers, its faces a lot of challenges in its development, implementation and continuous use. Several biotechnology discoveries had good prospects but failed to live-up to their expectation. A typical example of focus in this review is the case of Bacillus thuringiensis 3.

Bt’s Family Tree

Bt is a member of the genus Bacillus, a diverse group of gram-positive, aerobic, spore-forming bacteria consisting of more than 20 species that differ in their basic biological properties. In addition to Bt, the most important species are B. subtilis, a source of industrial enzymes; B. cereus; and B. anthracis, the causative agent of anthrax 4.

Mechanisms of Action and Resistance

BT insecticides, whether in the form of a spray or a Bt crop, does not function on contact as most chemical insecticides do, but rather, as mid gut toxins. They must be ingested by the target organism to be effective, and killing takes hours to days, longer than is required for synthetic insecticides.

In Bt crops, the plant tissues produce specific ICPs (insecticidal crystal protein) in a soluble form. In either case, the active ICP then traverses the peritrophic membrane and binds to specific receptors on the mid gut epithelium, forming pores and leading to loss of the transmembrane potential, cell lysis, leakage of the mid gut contents, paralysis, and death of the insect. One level of specificity in this interaction is provided by the mid gut environment of the insect, and a second by the binding of ICPs only to membranes carrying the appropriately matched receptors.

BACILLUS T Technology – Bt Cotton

Cotton plants transformed with the Bt gene do express the Bt toxin which provides some protection for the plant against bollworm pests. In seasons where serious bollworm outbreaks occur, Bt technology can help to prevent major crop losses. Seasonal variation may also have important implications in terms of risk, especially for poorer farmers. Beneficial outcomes depend on a diverse range of technical and institutional factors, which include the performance and local adaptation of the background variety into which the new genetic traits have been introduced as well as local agro-ecological, socio-economic, political and institutional factors 5.

Failures of Bacillus thuringiensis

A few specific claims have been made about the performance of Bt cotton, relating to yields, productivity and reductions in pesticide use. On the question of yields, substantial improvements in average yields and overall cotton output have been observed at the aggregate level. However, Bt insect resistance is not an intrinsically yield-enhancing trait. It can be regarded as a form of insurance against pest attack. As such, it can spread risk, but in seasons when pest pressure is not serious, Bt-adopters may end up having paid more for their GM seeds without the compensating benefit of an improved yield. In seasons with heavy pest pressure, by mitigating yield losses Bt technology can make cotton farming a bit more dependable 6.

Another disadvantage of topical Bt pesticides is their short window of effectiveness, and the fact that inclement weather can render Bt sprays useless within a matter of hours. Topical Bt sprays must therefore be reapplied several times in a growing season to reach the entire larval pest population, increasing the amount of product that needs to be used and the fuel needed for spraying. A potential solution to this problem was developed in the mid-1980s when scientists introduced Bt cry genes into tobacco and tomato plants and expressed the proteins directly in plant tissues 7. However, it offers no protection against unrelated threats, such as drought or an outbreak of ‘secondary’ pests. Having paid more for his or her seed, a Bt-adopter is potentially even more vulnerable than a non-adopter in the face of such eventualities.

A more robust claim is that Bt cotton contributes to improved productivity (that is, the ratio of outputs to inputs), even if yields are not actually greater. There is some weight to this claim, which makes agronomic sense. However, the estimated size of Bt cotton’s productivity advantage has been revised downwards in successive steps, from early and rather extravagant claims that were based on field trials, to more modest estimates based on farm survey data, and to even more modest levels once factors such as soil quality, the availability of irrigation, household assets and credit, and farmer skill and experience were taken into account 8.

Irrigation, in particular, has a large effect on yields and productivity for both Bt and non-Bt cotton. Where irrigation is lacking, yields for both types of cotton remain low, especially when soil quality is also poor 8. This raises questions about just how substantial any potential advantage of Bt technology really is, in practice, and whether those advantages are readily available to resource-poor farmers as well as those with better access to key inputs and resources 8.

One of the most consistent and seemingly robust claims made in the Bt cotton impacts literature is that Bt cotton reduces or enables a reduction in pesticide use. On the contrary, it is clear that many Bt cotton farmers in China, for example, still spray excessive quantities of pesticides and that dramatic reductions in pesticide use, as well as effective and economical pest control, have been achieved without Bt cotton.

Serious questions are also now emerging about the medium- and long term ecological and economic sustainability of transgenic Bt as a pest management tool. The adoption of Bt cotton has not necessarily resulted in a shift to more environmentally friendly or less hazardous pest-control methods overall. Unfortunately, though unsurprisingly, Chinese cotton farmers are now facing a surge in the numbers of formerly secondary insect pests, notably mirids, with Bt cotton fields evidently serving as a reservoir for mirids that attack cotton and other crops at a regional scale 8.

Bt cottonseed is significantly more expensive than conventional seed, the financial consequences of crop failure are likely to represent an elevated risk for the poorest farmers. For such farmers, who have good reason to be risk-averse, chemical pesticides may remain a more flexible and financially prudent pest-management tool than transgenic Bt 9.

Sometimes, however, the editorial line in favour of GM crops is more obviously on display. A good example of this arose in the case of a research paper first presented at a conference in 2006 by a team of researchers from Cornell University, USA, entitled ‘Tarnishing Silver Bullets’, reported data from a survey of cotton areas of China which found that the early benefits of Bt cotton cultivation in that country were being undermined by the emergence of secondary pests. The outbreak of sucking pests meant that Bt cotton was proving uneconomic for farmers, just a few years after they had adopted it; the study found that the net revenue of Bt farmers was actually lower than that of non-Bt farmers in 2004, because they had to spray additional pesticides as well as paying the higher price for Bt cotton seed.

India has been a major battleground for international disputes over the impacts of Bt cotton. Indian campaigners and commentators have claimed that many farmers in certain districts of two important cotton states, Andhra Pradesh and Maharashtra, had experienced poor yields and crop failures after planting Bt cotton; anti-GM activists in India and elsewhere have sought to link Bt cotton to an alleged surge in farmer suicides 10. Naturally, Bt cotton could not be solely responsible for the seasonal increases in farmer suicides, but the high price of the technology combined with the manner in which it was promoted to farmers and its failure to produce good yields very probably contributed to some farmers’ indebtedness and distress 11.

CONCLUSION

Official and commercial encouragement to embrace Bt cotton had been based in part on economic models of the technology’s likely impact that were built on the obviously false premise that cotton farmers only need to take account of one pest. The model therefore systematically overstated Bt cotton’s likely benefits. There is some evidence that, the technology helps to smooth out the seasonal fluctuations in cotton yields, making farming a little more predictable. Beyond that, however, unambiguous advantages for small cotton farmers are harder to identify.

The performance of transgenic crops in the developing world has varied widely, across farms and farmers, crop varieties, regions and seasons. The high degree of variability in outcomes points to possible issues of socio-economic differentiation in farmers’ capacities to exploit the technology to their advantage.

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