Host resistance to Bacillus thuringiensis is linked to altered bacterial community within a specialist insect herbivore (original) (raw)
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Continuous evolution of Bacillus thuringiensis toxins overcomes insect resistance
2016
The expression of insecticidal proteins from B. thuringiensis (Bt toxins) in crops has proved to be a valuable strategy for agricultural pest management1. Bt-toxin-producing crops have been widely adopted in agriculture with substantial economic and environmental benefits2, and have increased global agricultural productivity by an estimated US$78 billion from 1996 to 2013 (ref. 3). Unfortunately, Bt toxin resistance has evolved among insect pests and threatens the continued success of this strategy for pest control4. While resistance management strategies have been developed, including the use of multiple Bt toxins and preserving susceptible alleles in insect populations, the evolution of insect resistance to Bt toxins remains the most serious current threat to sustaining the gains offered by transgenic crops4. Bt toxins interact with protein receptors on the surface of insect midgut cells, leading to pore formation in the cell membrane and cell death5. Bt toxin resistance is common...
Insect resistance to Bacillus thuringiensis: uniform or diverse
Philosophical Transactions of The Royal Society B: Biological Sciences, 1998
Resistance to the insecticidal proteins produced by the soil bacterium Bacillus thuringiensis (Bt) has been documented in more than a dozen species of insect. Nearly all of these cases have been produced primarily by selection in the laboratory, but one pest, the diamondback moth (Plutella xylostella), has evolved resistance in open-¢eld populations. Insect resistance to Bt has immediate and widespread signi¢cance because of increasing reliance on Bt toxins in genetically engineered crops and conventional sprays. Furthermore, intense interest in Bt provides an opportunity to examine the extent to which evolutionary pathways to resistance vary among and within species of insect. One mode of resistance to Bt is characterized by more than 500-fold resistance to at least one Cry1A toxin, recessive inheritance, little or no cross-resistance to Cry1C, and reduced binding of at least one Cry1A toxin. Analysis of resistance to Bt in the diamondback moth and two other species of moths suggests that although this particular mode of resistance may be the most common, it is not the only means by which insects can attain resistance to Bt.
The impact of secondary pests on Bacillus thuringiensis (Bt) crops
Plant biotechnology journal, 2015
The intensification of agriculture and the development of synthetic insecticides enabled worldwide grain production to more than double in the last third of the 20th century. However, the heavy dependence and, in some cases, overuse of insecticides has been responsible for negative environmental and ecological impacts across the globe, such as a reduction in biodiversity, insect resistance to insecticides, negative effects on nontarget species (e.g. natural enemies) and the development of secondary pests. The use of recombinant DNA technology to develop genetically engineered insect-resistant crops could mitigate many of the negative side effects of insecticides. One such genetic alteration enables crops to express toxic crystalline (Cry) proteins from the soil bacteria Bacillus thuringiensis (Bt). Despite the widespread adoption of Bt crops, there are still a range of unanswered questions concerning longer term agro-ecosystem interactions. For instance, insect species that are not ...
Understanding the impact of Bacillus thuringiensis proteins on non-target organisms
International Journal of Scientific Research in Biological Sciences
Bacillus thuringiensis (Bt) is a spore-forming, gram-positive, aerobic, rod-shaped bacterium. During sporulation, Bt produces proteinaceous crystals called Cry proteins that are lethal to many insects' species, so are commonly used as biological pesticide. Transgenic Bt crops are genetically altered to express insecticidal toxins that cause fatality of a number of general agricultural pests. The insecticidal toxins formed by Bt crops possess narrow range of toxicity and therefore less non-target impacts as compared to conventional insecticides. A decrease in the amount and regularity of insecticide applications are financially advantageous. In numerous regions of the world, insecticide inputs have been significantly reduced because of Bt. The use of Bt crop technology might help in worldwide food security by escalating the amount and steadiness of crop yields. Though impact of Bt toxin on non-targeted organism is a serious issue yet no conclusion could still be drawn from several studies. This review summarizes the benefits of Bt crops including the impact on non-targeted organisms and Bt toxins having potential risks with respect to the environment.
BACILLUS THURINGIENSIS: THE BIOCONTROL AGENT IN A FOOD WEB PERSPECTIVE
Bacillus thuringiensis (Bt) is a facultative anaerobic, motile, gram-positive, spore-forming soil bacterium. The spores have parasporal inclusions made of different insecticidal crystal proteins (ICP), predominantly comprising one or more Cry and ⁄ or Cyt proteins (also known as δ-endotoxins) that have potent and specific insecticidal activity. The insecticidal properties of Bt have been known for over a century and commercial products based on this organism have been available for 70 years, occupying >90% of the biopesticide market. The microbe formulations have great potential in IPM programmes as has become the leading biopesticide in commercial agriculture, forest management and mosquito control. This bacterium is also a key source of genes for transgenic expression to provide pest resistance in plants and microorganisms as pest control agents in genetically modified organisms. Bt may persist as a component of the natural microflora after application to an ecosystem. Owing to their specific mode of action, Bt products are unlikely to pose any hazard to vertebrates or to the great majority of nontarget invertebrates. Yet many carnivorous arthropods and other non target organisms come into contact with Bt toxins not via target herbivore, but via nontarget herbivores.. Understanding its role in the ecosystem is crucial in deriving the best out of this great biocontrol agent.
One Gene In Diamondback Moth Confers Resistance to Four Bacillus Thuringiensis Toxins
Proceedings of the …, 1997
Environmentally benign insecticides derived from the soil bacterium Bacillus thuringiensis (Bt) are the most widely used biopesticides, but their success will be short-lived if pests quickly adapt to them. The risk of evolution of resistance by pests has increased, because transgenic crops producing insecticidal proteins from Bt are being grown commercially. Efforts to delay resistance with two or more Bt toxins assume that independent mutations are required to counter each toxin. Moreover, it generally is assumed that resistance alleles are rare in susceptible populations. We tested these assumptions by conducting single-pair crosses with diamondback moth (Plutella xylostella), the first insect known to have evolved resistance to Bt in open field populations. An autosomal recessive gene conferred extremely high resistance to four Bt toxins (Cry1Aa, Cry1Ab, Cry1Ac, and Cry1F). The finding that 21% of the individuals from a susceptible strain were heterozygous for the multiple-toxin resistance gene implies that the resistance allele frequency was 10 times higher than the most widely cited estimate of the upper limit for the initial frequency of resistance alleles in susceptible populations. These findings suggest that pests may evolve resistance to some groups of toxins much faster than previously expected. The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked ''advertisement'' in accordance with 18 U.S.C. §1734 solely to indicate this fact.
Critical Reviews in Plant Sciences, 2004
The aim of resistance management is to slow and ideally reverse the development of resistance in the pest population. Since 1996, million of acres of crops have been planted that are genetically engineered with Bacillus thuringiensis (Bt) for insect resistance. The novelty for resistance management is that with Bt technology it is possible to control the principal force in an agroecosystem microevolutionary process from the outset, i.e., selection pressure. In Bt crops, the toxin can be expressed constitutively at a relatively constant dose or expression of the toxin can be restricted to specific crop stages, tissues, or both. Here we propose that more precise control of selection eases the practical application of resistance management strategies (high-dose-refugia) compared to other resistance strategies. The population genetics and ecological and operational factors related to the high-dose-refugia strategy currently used for Bt crops are also reviewed.
Midgut Bacteria Required for Bacillus thuringiensis Insecticidal Activity
Proceedings of The National Academy of Sciences, 2006
Bacillus thuringiensis is the most widely applied biological insecticide and is used to manage insects that affect forestry and agriculture and transmit human and animal pathogens. This ubiquitous spore-forming bacterium kills insect larvae largely through the action of insecticidal crystal proteins and is commonly deployed as a direct bacterial spray. Moreover, plants engineered with the cry genes encoding the B. thuringiensis crystal proteins are the most widely cultivated transgenic crops. For decades, the mechanism of insect killing has been assumed to be toxin-mediated lysis of the gut epithelial cells, which leads to starvation, or B. thuringiensis septicemia. Here, we report that B. thuringiensis does not kill larvae of the gypsy moth in the absence of indigenous midgut bacteria. Elimination of the gut microbial community by oral administration of antibiotics abolished B. thuringiensis insecticidal activity, and reestablishment of an Enterobacter sp. that normally resides in the midgut microbial community restored B. thuringiensis-mediated killing. Escherichia coli engineered to produce the B. thuringiensis insecticidal toxin killed gypsy moth larvae irrespective of the presence of other bacteria in the midgut. However, when the engineered E. coli was heat-killed and then fed to the larvae, the larvae did not die in the absence of the indigenous midgut bacteria. E. coli and the Enterobacter sp. achieved high populations in hemolymph, in contrast to B. thuringiensis, which appeared to die in hemolymph. Our results demonstrate that B. thuringiensis-induced mortality depends on enteric bacteria.
Proceedings of the National Academy of Sciences, 1997
Insecticidal proteins from the soil bacterium Bacillus thuringiensis (Bt) are becoming a cornerstone of ecologically sound pest management. However, if pests quickly adapt, the benefits of environmentally benign Bt toxins in sprays and genetically engineered crops will be short-lived. The diamondback moth (Plutella xylostella) is the first insect to evolve resistance to Bt in open-field populations. Here we report that populations from Hawaii and Pennsylvania share a genetic locus at which a recessive mutation associated with reduced toxin binding confers extremely high resistance to four Bt toxins. In contrast, resistance in a population from the Philippines shows multilocus control, a narrower spectrum, and for some Bt toxins, inheritance that is not recessive and not associated with reduced binding. The observed variation in the genetic and biochemical basis of resistance to Bt, which is unlike patterns documented for some synthetic insecticides, profoundly affects the choice of strategies for combating resistance.