Showing papers on "Bacillus thuringiensis published in 2008"
TL;DR: Analysis of more than a decade of global monitoring data reveals that the frequency of resistance alleles has increased substantially in some field populations of Helicoverpa zea, but not in five other major pests in Australia, China, Spain and the United States.
Abstract: Evolution of insect resistance threatens the continued success of transgenic crops producing Bacillus thuringiensis (Bt) toxins that kill pests. The approach used most widely to delay insect resistance to Bt crops is the refuge strategy, which requires refuges of host plants without Bt toxins near Bt crops to promote survival of susceptible pests. However, large-scale tests of the refuge strategy have been problematic. Analysis of more than a decade of global monitoring data reveals that the frequency of resistance alleles has increased substantially in some field populations of Helicoverpa zea, but not in five other major pests in Australia, China, Spain and the United States. The resistance of H. zea to Bt toxin Cry1Ac in transgenic cotton has not caused widespread crop failures, in part because other tactics augment control of this pest. The field outcomes documented with monitoring data are consistent with the theory underlying the refuge strategy, suggesting that refuges have helped to delay resistance.
727 citations
TL;DR: Analysis of the population dynamics of H. armigera from 1992 to 2007 in China indicated that a marked decrease in regional outbreaks of this pest in multiple crops was associated with the planting of Bt cotton, which may reduce its presence on other host crops and the need for insecticide sprays in general.
Abstract: Transgenic cotton that has been engineered to produce insecticidal toxins from Bacillus thuringiensis (Bt) and so to resist the pest cotton bollworm (Helicoverpa armigera) has been widely planted in Asia. Analysis of the population dynamics of H. armigera from 1992 to 2007 in China indicated that a marked decrease in regional outbreaks of this pest in multiple crops was associated with the planting of Bt cotton. The study area included six provinces in northern China with an annual total of 3 million hectares of cotton and 22 million hectares of other crops (corn, peanuts, soybeans, and vegetables) grown by more than 10 million resource-poor farmers. Our data suggest that Bt cotton not only controls H. armigera on transgenic cotton designed to resist this pest but also may reduce its presence on other host crops and may decrease the need for insecticide sprays in general.
663 citations
TL;DR: This review discusses the available data on the effects of Cry proteins on below-ground organisms, the fate of these proteins in soil, the techniques and indicators that are available to study these aspects, and future directions.
Abstract: Recent applications of biotechnology, especially genetic engineering, have revolutionized crop improvement and increased the availability of valuable new traits. A current example is the use of the insecticidal Cry proteins from the bacterium, Bacillus thuringiensis (Bt), to improve crops, known as Bt crops, by reducing injury from various crop pests. The adoption of genetically modified (GM) crops has increased dramatically in the last 11 years. However, the introduction of GM plants into agricultural ecosystems has raised a number of questions, including the ecological impact of these plants on soil ecosystems. Crop residues are the primary source of carbon in soil, and root exudates govern which organisms reside in the rhizosphere. Therefore, any change to the quality of crop residues and rhizosphere inputs could modify the dynamics of the composition and activity of organisms in soil. Insect-resistant Bt crops have the potential to change the microbial dynamics, biodiversity, and essential ecosystem functions in soil, because they usually produce insecticidal Cry proteins through all parts of the plant. It is crucial that risk assessment studies on the commercial use of Bt crops consider the impacts on organisms in soil. In general, few or no toxic effects of Cry proteins on woodlice, collembolans, mites, earthworms, nematodes, protozoa, and the activity of various enzymes in soil have been reported. Although some effects, ranging from no effect to minor and significant effects, of Bt plants on microbial communities in soil have been reported, using both culturing and molecular techniques, they were mostly the result of differences in geography, temperature, plant variety, and soil type and, in general, were transient and not related to the presence of the Cry proteins. The respiration (i.e., CO2 evolution) of soils cultivated with Bt maize or amended with biomass of Bt maize and other Bt crops was generally lower than from soils cultivated with or amended with biomass of the respective non-Bt isolines, which may have been a result of differences in chemical composition (e.g., the content of starch, soluble N, proteins, carbohydrates, lignin) between Bt plants and their near-isogenic counterparts. Laboratory and field studies have shown differences in the persistence of the Cry proteins in soil, which appear to be the result primarily of differences in microbial activity, which, in turn, is dependent on soil type (e.g., pH, clay mineral composition, other physicochemical characteristics), season (e.g., temperature, water tension), crop species (e.g., chemical composition, C:N ratio, plant part), crop management practices (e.g., till vs. no-till), and other environmental factors that vary with location and climate zones. This review discusses the available data on the effects of Cry proteins on below-ground organisms, the fate of these proteins in soil, the techniques and indicators that are available to study these aspects, and future directions.
340 citations
TL;DR: No uniform effects of Bt cotton, maize and potato on the functional guilds of non-target arthropods are found and the importance of using controls not only to isolate the effects of a Bt crop per se but also to reflect the replacement of existing agricultural practices is highlighted.
Abstract: Background
Uncertainty persists over the environmental effects of genetically-engineered crops that produce the insecticidal Cry proteins of Bacillus thuringiensis (Bt). We performed meta-analyses on a modified public database to synthesize current knowledge about the effects of Bt cotton, maize and potato on the abundance and interactions of arthropod non-target functional guilds.
Methodology/Principal Findings
We compared the abundance of predators, parasitoids, omnivores, detritivores and herbivores under scenarios in which neither, only the non-Bt crops, or both Bt and non-Bt crops received insecticide treatments. Predators were less abundant in Bt cotton compared to unsprayed non-Bt controls. As expected, fewer specialist parasitoids of the target pest occurred in Bt maize fields compared to unsprayed non-Bt controls, but no significant reduction was detected for other parasitoids. Numbers of predators and herbivores were higher in Bt crops compared to sprayed non-Bt controls, and type of insecticide influenced the magnitude of the difference. Omnivores and detritivores were more abundant in insecticide-treated controls and for the latter guild this was associated with reductions of their predators in sprayed non-Bt maize. No differences in abundance were found when both Bt and non-Bt crops were sprayed. Predator-to-prey ratios were unchanged by either Bt crops or the use of insecticides; ratios were higher in Bt maize relative to the sprayed non-Bt control.
Conclusions/Significance
Overall, we find no uniform effects of Bt cotton, maize and potato on the functional guilds of non-target arthropods. Use of and type of insecticides influenced the magnitude and direction of effects; insecticde effects were much larger than those of Bt crops. These meta-analyses underscore the importance of using controls not only to isolate the effects of a Bt crop per se but also to reflect the replacement of existing agricultural practices. Results will provide researchers with information to design more robust experiments and will inform the decisions of diverse stakeholders regarding the safety of transgenic insecticidal crops.
304 citations
TL;DR: Possible mechanisms of resistance and different strategies to cope with resistance, such as expression of several toxins with different modes of action in the same plant, modified Cry toxins active against resistant insects, and the potential use of Cyt toxins or a fragment of cadherin receptor are reviewed.
266 citations
TL;DR: The results suggest that rapid response to selection is possible in the absence of mating with unexposed beetles, emphasizing the importance of effective refuges for resistance management.
Abstract: To delay evolution of insect resistance to transgenic crops producing Bacillus thuringiensis (Bt) toxins, nearby "refuges" of host plants not producing Bt toxins are required in many regions. Such refuges are expected to be most effective in slowing resistance when the toxin concentration in Bt crops is high enough to kill all or nearly all insects heterozygous for resistance. However, Bt corn, Zea mays, introduced recently does not meet this "high-dose" criterion for control of western corn rootworm (WCR), Diabrotica virgifera virgifera. A greenhouse method of rearing WCR on transgenic corn expressing the Cry3Bb1 protein was used in which approximately 25% of previously unexposed larvae survived relative to isoline survival (compared to 1-4% in the field). After three generations of full larval rearing on Bt corn (Constant-exposure colony), WCR larval survival was equivalent on Bt corn and isoline corn in greenhouse trials, and the LC(50) was 22-fold greater for the Constant-exposure colony than for the Control colony in diet bioassays with Cry3Bb1 protein on artificial diet. After six generations of greenhouse selection, the ratio of larval recovery on Bt corn to isoline corn in the field was 11.7-fold greater for the Constant-exposure colony than the Control colony. Removal from selection for six generations did not decrease survival on Bt corn in the greenhouse. The results suggest that rapid response to selection is possible in the absence of mating with unexposed beetles, emphasizing the importance of effective refuges for resistance management.
202 citations
TL;DR: The hypothesis that Bt infection increases the level of oxidative stress in the larval midgut in Galleria mellonella larvae is confirmed and it seems possible that oxidative damage contributes to cell death in the midGut during bacteriosis.
Abstract: Bacillus thuringiensis is one of the most widely used sources of biorational pesticides, as well as a key source of genes for transgenic expression to provide pest resistance in plants. In this study the effect of Bacillus thuringiensis ssp. galleriae (Bt) infection on the activity of superoxide dismutase (SOD), glutathione S-transferase (GST), catalase (CAT), concentrations of oxidated and reduced thiols (RSSR/RSH) and malondialdehyde (MDA) was tested in the midgut of Galleria mellonella larvae. We found that Bt infection resulted in increased activities of SOD, GST, malondialdehyde and RSSR/RSH ratio the first day after inoculation. However, catalase activity decreased on the first and following days after bacterial infection by Bt. Our results confirm the hypothesis that Bt infection increases the level of oxidative stress in the larval midgut. In light of this study, it seems possible that oxidative damage contributes to cell death in the midgut during bacteriosis.
198 citations
TL;DR: After 4 consecutive years of corn cultivation, there were, in general, no consistent statistically significant differences in the numbers of different groups of microorganisms, the activities of the enzymes, and the pH between soils planted with Bt and non-Bt corn.
Abstract: Transgenic Bt crops produce insecticidal Cry proteins that are released to soil in plant residues, root exudates, and pollen and that may affect soil microorganisms. As a continuation of studies in the laboratory and a plant-growth room, a field study was conducted at the Rosemount Experiment Station of the University of Minnesota. Three Bt corn varieties that express the Cry1Ab protein, which is toxic to the European corn borer (Ostrinia nubilalis Hubner), and one Bt corn variety that expresses the Cry3Bb1 protein, which is toxic to the corn rootworm complex (Diabrotica spp.), and their near-isogenic non-Bt varieties were evaluated for their effects on microbial diversity by classical dilution plating and molecular (polymerase chain reaction-denaturing gradient gel electrophoresis) techniques and for the activities of some enzymes (arylsulfatases, acid and alkaline phosphatases, dehydrogenases, and proteases) involved in the degradation of plant biomass. After 4 consecutive years of corn cultivation (2003-2006), there were, in general, no consistent statistically significant differences in the numbers of different groups of microorganisms, the activities of the enzymes, and the pH between soils planted with Bt and non-Bt corn. Numbers and types of microorganisms and enzyme activities differed with season and with the varieties of corn, but these differences were not related to the presence of the Cry proteins in soil. The Cry1Ab protein of Bt corn (events Bt11 and MON810) was detected in most soils during the 4 yr, whereas the Cry3Bb1 protein was not detected in soils of Bt corn (event MON863) expressing the cry3Bb1 gene.
142 citations
TL;DR: The results help explain the observed differences between Bollgard and Bollgard II mortality against the primary lepidopteran cotton pests, and they may lead to improved scouting and resistance management practices, and to more effective control of these pests with Bt transgenic crops in the future.
Abstract: Cry1Ac protoxin (the active insecticidal toxin in both Bollgard and Bollgard II cotton [Gossypium hirsutum L.]), and Cry2Ab2 toxin (the second insecticidal toxin in Bollgard II cotton) were bioassayed against five of the primary lepidopteran pests of cotton by using diet incorporation. Cry1Ac was the most toxic to Heliothis virescens (F.) and Pectinophora gossypiella (Saunders), demonstrated good activity against Helicoverpa zea (Boddie), and had negligible toxicity against Spodoptera exigua (Hubner) and Spodoptera frugiperda (J. E. Smith). Cry2Ab2 was the most toxic to P. gossypiella and least toxic to S. frugiperda. Cry2Ab2 was more toxic to S. exigua and S. frugiperda than Cry1Ac. Of the three insect species most sensitive to both Bacillus thuringiensis (Bt) proteins (including H. zea), P. gossypiella was only three-fold less sensitive to Cry2Ab2 than Cry1Ac, whereas H. virescens was 40-fold less sensitive to Cry2Ab2 compared with CrylAc. Cotton plants expressing Cry1Ac only and both Cry1Ac and Cry2Ab2 proteins were characterized for toxicity against H. zea and S.frugiperda larvae in the laboratory and H. zea larvae in an environmental chamber. In no-choice assays on excised squares from plants of different ages, second instar H. zea larvae were controlled by Cry1Ac/Cry2Ab2 cotton with mortality levels of 90% and greater at 5 d compared with 30-80% mortality for Cry1Ac-only cotton, depending on plant age. Similarly, feeding on leaf discs from Cry1Ac/Cry2Ab2 cotton resulted in mortality of second instars of S.frugiperda ranging from 69 to 93%, whereas exposure to Cry1Ac-only cotton yielded 20-69% mortality, depending on plant age. When cotton blooms were infested in situ in an environmental chamber with neonate H. zea larvae previously fed on synthetic diet for 0, 24, or 48 h, 7-d flower abortion levels for Cry1Ac-only cotton were 15, 41, and 63%, respectively, whereas for Cry1Ac/Cry2Ab2 cotton, flower abortion levels were 0, 0, and 5%, respectively. Cry1Ac and Cry2Ab2 concentrations were measured within various cotton tissues of Cry1Ac-only and Cry1Ac/Cry2Ab2 plants, respectively, by using enzyme-linked immunosorbent assay. Terminal leaves significantly expressed the highest, and large leaves, calyx, and bracts expressed significantly the lowest concentrations of Cry1Ac, respectively. Ovules expressed significantly the highest, and terminal leaves, large leaves, bracts, and calyx expressed significantly (P < 0.05) the lowest concentrations of Cry2Ab2. These results help explain the observed differences between Bollgard and Bollgard II mortality against the primary lepidopteran cotton pests, and they may lead to improved scouting and resistance management practices, and to more effective control of these pests with Bt transgenic crops in the future.
136 citations
TL;DR: Thirty five bacterial isolates from diverse environmental sources such as contaminated food, nitrogen rich soil, activated sludges from pesticide and oil refineries effluent treatment plants were found to belong to Bacillus, Bordetella, Enterobacter, Proteus, and Pseudomonas sp.
129 citations
TL;DR: The aim of this review is to provide an overview of the use of Bt for crop protection and to deal with the problem of the emergence of insects resistant to this biopesticide.
Abstract: Bacillus thuringiensis (Bt) is a sporulating, Gram-positive facultative-aerobic soil bacterium. Its principal characteristic is the synthesis, during sporulation, of a crystalline inclusion containing proteins known as δ-endotoxins or Cry proteins. These proteins have insecticidal properties. The considerable diversity of these toxins, their efficacy and their relatively cheap production have made Bt the most widely used biopesticide in the world. It is used in the fight against many agricultural crop pests – mostly lepidopteran and coleopteran larvae – notably in the creation of new plant varieties expressing Bt cry genes. For human health, Bt can be used for the effective control of populations of several dipteran disease vectors. The aim of this review is to provide an overview of the use of Bt for crop protection and to deal with the problem of the emergence of insects resistant to this biopesticide. We will begin by presenting various aspects of the biology of this entomopathogenic micro-organism, focusing on the diversity and mode of action of the insecticidal toxins it produces. We will then present several examples of utilization of commercially available Bt products used as sprays or as transgenic crops. Finally, we will describe the principal strategy for the use of Bt transgenic plants, developed so as to prevent or delay the emergence of resistance in target insect populations.
01 Jan 2008
TL;DR: Of the several strategies considered, a high dose of the insecticidal protein along with an adjacent refuge plot of non-Bt plants has been chosen as the most effective and will likely confer maximum protection to the Bt crop technology against insect resistance.
Abstract: Economically important crops, such as maize and cotton, have been transformed with genes encoding insecticidal proteins from Bacillus thuringiensis (Bt) to confer them protection against the most important insect pests. Of the 114 million hectares globally planted with GM crops in 2007, over one third are insect-resistant Bt crops, and the area keeps increasing every year. The potential for insects to evolve resistance to GM insecticidal plants is considered to be one of the main threats to this technology, since resistance to Bt sprayable products has been demonstrated. Insect resistance management plans for this new class of pesticides are encouraged and became mandatory in the USA. Of the several strategies considered, a high dose of the insecticidal protein along with an adjacent refuge plot of non-Bt plants has been chosen as the most effective. Second generation Bt cotton combines two insecticidal proteins with unique target sites. Such “pyramided” Bt crops hold great promise and, in combination with the high dose/refuge strategy, will likely confer maximum protection to the Bt crop technology against insect resistance. So far, no case of resistance evolution to Bt crops has been reported.
TL;DR: The results provide the first clear evidence of the lack of hazard to a parasitoid by a Bt plant, compared to traditional insecticides, and describe a test to rigorously evaluate the risks Bt plants pose to predators and parasitoids.
Abstract: The ecological safety of transgenic insecticidal plants expressing crystal proteins (Cry toxins) from the bacterium Bacillus thuringiensis (Bt) continues to be debated. Much of the debate has focused on nontarget organisms, especially predators and parasitoids that help control populations of pest insects in many crops. Although many studies have been conducted on predators, few reports have examined parasitoids but some of them have reported negative impacts. None of the previous reports were able to clearly characterize the cause of the negative impact. In order to provide a critical assessment, we used a novel paradigm consisting of a strain of the insect pest, Plutella xylostella (herbivore), resistant to Cry1C and allowed it to feed on Bt plants and then become parasitized by Diadegma insulare, an important endoparasitoid of P. xylostella. Our results indicated that the parasitoid was exposed to a biologically active form of the Cy1C protein while in the host but was not harmed by such exposure. Parallel studies conducted with several commonly used insecticides indicated they significantly reduced parasitism rates on strains of P. xylostella resistant to these insecticides. These results provide the first clear evidence of the lack of hazard to a parasitoid by a Bt plant, compared to traditional insecticides, and describe a test to rigorously evaluate the risks Bt plants pose to predators and parasitoids.
TL;DR: By this method, three cry genes—cry55Aa1, cry6Aa2, and cry5Ba2—were cloned from rice-shaped crystals, producing B. thuringiensis YBT-1518, which consists of 54- and 45-kDa crystal proteins.
Abstract: We have developed a strategy for isolating cry genes from Bacillus thuringiensis. The key steps are the construction of a DNA library in an acrystalliferous B. thuringiensis host strain and screening for the formation of crystal through optical microscopy observation and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analyses. By this method, three cry genes—cry55Aa1, cry6Aa2, and cry5Ba2—were cloned from rice-shaped crystals, producing B. thuringiensis YBT-1518, which consists of 54- and 45-kDa crystal proteins. cry55Aa1 encoded a 45-kDa protein, cry6Aa2 encoded a 54-kDa protein, and cry5Ba2 remained cryptic in strain YBT-1518, as shown by SDS-PAGE or microscopic observation. Proteins encoded by these three genes are all toxic to the root knot nematode Meloidogyne hapla. The two genes cry55Aa1 and cry6Aa2 were found to be located on a plasmid with a rather small size of 17.7 kb, designated pBMB0228.
TL;DR: Strains of Bacillus thuringiensis isolated from various food items and found to belong to either H‐serotype kurstaki or neoleonensis were found to express cytotoxic effects on Vero cells as an indicator of enterotoxin activity.
Abstract: P.H. DAMGAARD, H.D. LARSEN, B.M. HANSEN, J. BRESCIANI AND K. JORGENSEN. 1996. Strains of Bacillus thuringiensis were isolated from various food items (pasta, pitta bread and milk) and were found to belong to either H-serotype kurstaki or neoleonensis. The strains were bioassayed against Pieris brassicae and insecticidal activity of strains was found to correspond to the presence of the cry1.A-gene. All strains, except one, were found to express cytotoxic effects on Vero cells as an indicator of enterotoxin activity. Further, the B. thuringiensis strains HD-1 (serotype kurstuki), NB-125 (serotype tenebrionis) and HD-567 (serotype isruelensis) which are used commercially for insect pest management, were also found to have cytotoxic effects on Vero cells.
TL;DR: Lack of cross‐resistance between Cry1F and Cry1Ab suggest that maize hybrids expressing these two toxins are likely to be compatible for resistance management of O. nubilalis.
Abstract: Evolution of resistance by insect pests is the greatest threat to the continued success of Bacillus thuringiensis (Bt) toxins used in insecticide formulations or expressed by transgenic crop plants such as CrylF-expressing maize [(Zea mays L.) (Poaceae)]. A strain of European corn borer, Ostrinia nubilalis (Hiibner) (Lepidoptera: Crambidae), obtained from field collections throughout the central US Corn Belt in 1996 was selected in the laboratory for resistance to Cry1F by exposure to the toxin incorporated into artificial diet. The selected strain developed more than 3000-fold resistance to Cry1F after 35 generations of selection and readily consumed Cry1F expressing maize tissue; yet, it was as susceptible to CrylAb and Cry9C as the unselected control strain. Only a low level of cross-resistance (seven-fold) to CrylAc was observed. These lacks of cross-resistance between Cry1F and CrylAb suggest that maize hybrids expressing these two toxins are likely to be compatible for resistance management of O. nubilalis.
TL;DR: The first report of stable Cry1Ac resistance in H. zea is reported, aiding in understanding why this pest has not evolved B. thuringiensis resistance, and highlighting the need to choose carefully the form of B.Thurringiensis protein used in experiments.
Abstract: Laboratory-selected Bacillus thuringiensis-resistant colonies are important tools for elucidating B. thuringiensis resistance mechanisms. However, cotton bollworm, Helicoverpa zea, a target pest of transgenic corn and cotton expressing B. thuringiensis Cry1Ac (Bt corn and cotton), has proven difficult to select for stable resistance. Two populations of H. zea (AR and MR), resistant to the B. thuringiensis protein found in all commercial Bt cotton varieties (Cry1Ac), were established by selection with Cry1Ac activated toxin (AR) or MVP II (MR). Cry1Ac toxin reflects the form ingested by H. zea when feeding on Bt cotton, whereas MVP II is a Cry1Ac formulation used for resistance selection and monitoring. The resistance ratio (RR) for AR exceeded 100-fold after 11 generations and has been maintained at this level for nine generations. This is the first report of stable Cry1Ac resistance in H. zea. MR crashed after 11 generations, reaching only an RR of 12. AR was only partially cross-resistant to MVP II, suggesting that MVP II does not have the same Cry1Ac selection pressure as Cry1Ac toxin against H. zea and that proteases may be involved with resistance. AR was highly cross-resistant to Cry1Ab toxin but only slightly cross-resistant to Cry1Ab expressing corn leaf powder. AR was not cross-resistant to Cry2Aa2, Cry2Ab2-expressing corn leaf powder, Vip3A, and cypermethrin. Toxin-binding assays showed no significant differences, indicating that resistance was not linked to a reduction in binding. These results aid in understanding why this pest has not evolved B. thuringiensis resistance, and highlight the need to choose carefully the form of B. thuringiensis protein used in experiments.
TL;DR: Cross inhibition tests with bacteriocin producer strains and plasmid profiles indicated that entomocin 110 is a new bacteriOCin, which genetic determinants are probably harbored by the chromosome.
TL;DR: A novel cry1A was cloned from Bacillus thuringiensis strain BT8 and expressed in the B. thuringienis acrystalliferous mutant HD73(-), exhibiting high toxicity against lepidopteran larvae of Ostrinia furnacalis, Helicoverpa armigera, Chilo suppressalis, and Plutella xylostella.
Abstract: A novel cry1A was cloned from Bacillus thuringiensis strain BT8 and expressed in the B. thuringiensis acrystalliferous mutant HD73-. The gene, designated cry1Ah1, encoded a protein with a molecular weight of 134 kDa. Reverse transcriptase-PCR and Western blotting showed that Cry1Ah was expressed in the host strain BT8. The toxin expressed in HD73- exhibited high toxicity against lepidopteran larvae of Ostrinia furnacalis, Helicoverpa armigera, Chilo suppressalis, and Plutella xylostella. The 50% lethal concentrations (LC50s) were 0.05, 1.48, 0.98 µg g-1 and 1.52 µg mL-1, respectively. The LC50s of Cry1Ah were significantly lower than that of Cry1Ac for H. armigera, C. suppressalis, and O. furnacalis, and lower than that of Cry1Ab and Cry1Ie for Ostrinia furnacalis. The high toxicity against a range of pest species makes this novel toxin a potential candidate for insect biocontrol.
TL;DR: Nine of the most common lepidopteran active Cry proteins from Bacillus thuringiensis have been tested for activity against Spodoptera exigua and showed that Cry1Ca, Cry1Da, and Cry1Fa were the most effective toxins with all strains.
TL;DR: Results are evidence that the 106-kDa GPI-anchored APN is a specific binding protein, and a putative midgut receptor, for Bt Cry11Ba toxin.
Abstract: Bacillus thuringiensis (Bt) insecticidal toxins bind to receptors on midgut epithelial cells of susceptible insects, and binding triggers biochemical events that lead to insect mortality. Recently, a 100-kDa aminopeptidase N (APN) was isolated from brush border membrane vesicles (BBMV) of Anopheles quadrimaculatus and shown to bind Cry11Ba toxin with surface plasmon resonance (SPR) detection [Abdullah et al. (2006) BMC Biochem. 7, 16]. In our study, a 106-kDa APN, called AgAPN2, released by phosphatidylinositol-specific phospholipase C (PI-PLC) from Anopheles gambiae BBMV was extracted by Cry11Ba bound to beads. The AgAPN2 cDNA was cloned, and analysis of the predicted AgAPN2 protein revealed a zinc-binding motif (HEIAH), three potential N-glycosylation sites, and a predicted glycosylphosphatidylinositol (GPI) anchor site. Immunohistochemistry localized AgAPN2 to the microvilli of the posterior midgut. A 70-kDa fragment of the 106-kDa APN was expressed in Escherichia coli. When purified, it competitively ...
TL;DR: This is the first report of hybrid, lipocalin-like domains in shorter polycalin sequences that are not present in the longest sequence, and it is proposed that these hybrid domains are generated by alternative splicing of the mRNA.
TL;DR: The nature and origin of the high toxicity toward mosquito larvae found in decaying leaf litter collected in several natural mosquito breeding sites in the Rhône-Alpes region is determined and the issue of the persistence, potential proliferation and environmental accumulation of human-spread Bti in natural mosquito habitats is raised.
Abstract: Background The detrimental effects of chemical insecticides on the environment and human health have lead to the call for biological alternatives Today, one of the most promising solutions is the use of spray formulations based on Bacillus thuringiensis subsp israelensis (Bti) in insect control programs As a result, the amounts of Bti spread in the environment are expected to increase worldwide, whilst the common belief that commercial Bti is easily cleared from the ecosystem has not yet been clearly established Methodology/Main Findings In this study, we aimed to determine the nature and origin of the high toxicity toward mosquito larvae found in decaying leaf litter collected in several natural mosquito breeding sites in the Rhone-Alpes region From the toxic fraction of the leaf litter, we isolated B cereus-like bacteria that were further characterized as B thuringiensis subsp israelensis using PCR amplification of specific toxin genes Immunological analysis of these Bti strains showed that they belong to the H14 group We finally used amplified length polymorphism (AFLP) markers to show that the strains isolated from the leaf litter were closely related to those present in the commercial insecticide used for field application, and differed from natural worldwide genotypes Conclusions/Significance Our results raise the issue of the persistence, potential proliferation and environmental accumulation of human-spread Bti in natural mosquito habitats Such Bti environmental persistence may lengthen the exposure time of insects to this bio-insecticide, thereby increasing the risk of resistance acquisition in target insects, and of a negative impact on non-target insects
TL;DR: Results show that adults of C. carnea are not affected by Bt maize pollen and are not sensitive to Cry1Ab and Cry3Bb1 at concentrations exceeding the levels in pollen.
Abstract: Adults of the common green lacewing, Chrysoperla carnea (Stephens) (Neuroptera: Chrysopidae), are prevalent pollen-consumers in maize fields. They are therefore exposed to insecticidal proteins expressed in the pollen of insect-resistant, genetically engineered maize varieties expressing Cry proteins derived from Bacillus thuringiensis (Bt). Laboratory experiments were conducted to evaluate the impact of Cry3Bb1 or Cry1Ab-expressing transgenic maize (MON 88017, Event Bt176) pollen on fitness parameters of adult C. carnea. Adults were fed pollen from Bt maize varieties or their corresponding near isolines together with sucrose solution for 28 days. Survival, pre-oviposition period, fecundity, fertility and dry weight were not different between Bt or non-Bt maize pollen treatments. In order to ensure that adults of C. carnea are not sensitive to the tested toxins independent from the plant background and to add certainty to the hazard assessment, adult C. carnea were fed with artificial diet containing purified Cry3Bb1 or Cry1Ab at about a 10 times higher concentration than in maize pollen. Artificial diet containing Galanthus nivalis agglutinin (GNA) was included as a positive control. No differences were found in any life-table parameter between Cry protein containing diet treatments and control diet. However, the pre-oviposition period, daily and total fecundity and dry weight of C. carnea were significantly negatively affected by GNA-feeding. In both feeding assays, the stability and bioactivity of Cry proteins in the food sources as well as the uptake by C. carnea was confirmed. These results show that adults of C. carnea are not affected by Bt maize pollen and are not sensitive to Cry1Ab and Cry3Bb1 at concentrations exceeding the levels in pollen. Consequently, Bt maize pollen consumption will pose a negligible risk to adult C. carnea.
TL;DR: This paper summarized the relative progresses of B. thuringiensis in plant disease control and its favorable application prospects and revealed a new strategy against plant bacterial diseases by quenching bacterial quorum sensing.
Abstract: Bacillus thuringiensis is well known as an effective bio-insecticidal bacterium. However, the roles of B. thuringiensis to control plant diseases are not paid great attention to. In recent years, many new functions in protecting plants from pathogen infection have been discovered. For example, acyl homoserine lactone lactonase produced by B. thuringiensis can open the lactone ring of N-acyl homoserine lactone, a signal molecule in the bacterial quorum-sensing system. This in turn, significantly silences bacterial virulence. This finding resulted in the development of a new strategy against plant bacterial diseases by quenching bacterial quorum sensing. Another new discovery about B. thuringiensis function is zwittermicin A, a linear aminopolyol antibiotic with high activity against the Oomycetes and their relatives, as well as some gram-negative bacteria. This paper summarized the relative progresses of B. thuringiensis in plant disease control and its favorable application prospects.
TL;DR: It is demonstrated for the first time that a three-domain Cry protein can provide protection against a plant-endoparasitic nematode and that Cry proteins as a group have excellent potential as con- trol agents of plant-parasitic Nematodes.
TL;DR: It is concluded that reduced bollworm control efficacy under waterlogging or the combined stress could be mainly attributed to the declined levels of Bt protein, which is closely associated with the inhibited nitrogen metabolism by stresses.
TL;DR: Evaluating different Bt genes in the same rice variety in both the laboratory and the field and testing feeding behavior of rice insect to these Bt rice showed that 7-d-old larvae of Asiatic rice borer have the capacity to distinguish Bt and non-Bt culm cuttings and preferentially fed on non- Bt cutTings.
Abstract: Ten transgenic Bacillus thuringiensis Bt rice, Oryza sativa L., lines with different Bt genes (two Cry1Ac lines, three Cry2A lines, and five Cry9C lines) derived from the same variety Minghui 63 were evaluated in both the laboratory and the field. Bioassays were conducted by using the first instars of two main rice lepidopteran insect species: yellow stem borer, Scirpophaga incertulas (Walker) and Asiatic rice borer, Chilo suppressalis (Walker). All transgenic lines exhibited high toxicity to these two rice borers. Field evaluation results also showed that all transgenic lines were highly insect resistant with both natural infestation and manual infestation of the neonate larvae of S. incertulas compared with the nontransformed Minghui63. Bt protein concentrations in leaves of 10 transgenic rice lines were estimated by the sandwich enzyme-linked immunosorbent assay. The cry9C gene had the highest expression level, next was cry2A gene, and the cry1Ac gene expressed at the lowest level. The feeding behavior of 7-d-old Asiatic rice borer to three classes of Bt transgenic rice lines also was detected by using rice culm cuttings. The results showed that 7-d-old larvae of Asiatic rice borer have the capacity to distinguish Bt and non-Bt culm cuttings and preferentially fed on non-Bt cuttings. When only Bt culm cuttings with three classes of different Bt proteins (CrylAc, Cry2A, and Cry9C) were fed, significant distribution difference of 7-d-old Asiatic rice borer in culm cuttings of different Bt proteins also was found. In the current study, we evaluate different Bt genes in the same rice variety in both the laboratory and the field, and also tested feeding behavior of rice insect to these Bt rice. These data are valuable for the further development of two-toxin Bt rice and establishment of appropriate insect resistance management in the future.
TL;DR: Screening results in thirteen strains having more than one PGP trait showed that B. thuringiensis harbours and expresses several PGP determinants that could be very interesting in field application to enhance the plant growth.
Abstract: This study aimed to evaluate the plant growth promoting (PGP) potential ofBacillus thuringiensis. In this context, several genetic determinants of factors implicated in PGP potential were investigated by polymerase chain reaction (PCR) in 16B. thuringiensis strains of different origin and belonging to different subspecies. PCR screening was performed on acid phosphatase, phytase, siderophore biosynthesis protein, 1-aminocyclopropane-1-carboxylate (ACC) deaminase and indolpyruvate decarboxylase (ipdC). Production of indol acetic acid (IAA)-like compounds and of ACC deaminase, and capability of solubilising mineral phosphate were investigated by phenotypic tests. All the strains were PCR positive for the presence of the siderophore biosynthesis protein, ACC deaminase and acid phosphatase genes. Five and seven strains gave an amplicon with the expected length for the phytase andipdC genes respectively. All the strains produced IAA compounds and seven had a high capacity to solubilise inorganic phosphorous. Qualitative phenotypic test for ACC deaminase activity showed that seven strains are able to grow on salt minimal medium containing ACC as sole nitrogen source, indicating the expression of theaccd genes. Our screening results in thirteen strains having more than one PGP trait and showed thatB. thuringiensis harbours and expresses several PGP determinants that could be very interesting in field application to enhance the plant growth. To our knowledge, this is the first report on the multiple plant growth promoting potential ofB. thuringiensis.