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Showing papers on "Bacillus thuringiensis published in 2021"


Journal ArticleDOI
TL;DR: A review of the current knowledge on mechanisms of resistance to Bt toxins, with emphasis on key resistance genes and field-evolved resistance, to support improvement of Bt technology and its sustainability is presented in this paper.
Abstract: Insecticidal proteins from the bacterium Bacillus thuringiensis (Bt) are used in sprayable formulations or produced in transgenic crops as the most successful alternatives to synthetic pesticides. The most relevant threat to sustainability of Bt insecticidal proteins (toxins) is the evolution of resistance in target pests. To date, high-level resistance to Bt sprays has been limited to one species in the field and another in commercial greenhouses. In contrast, there are currently seven lepidopteran and one coleopteran species that have evolved practical resistance to transgenic plants producing insecticidal Bt proteins. In this article, we present a review of the current knowledge on mechanisms of resistance to Bt toxins, with emphasis on key resistance genes and field-evolved resistance, to support improvement of Bt technology and its sustainability.

106 citations


Journal ArticleDOI
TL;DR: In this article, the authors demonstrate that Bacillus thuringiensis RZ2MS9 harbours the complete set of genes required in two pathways that are used for Indole acetic acid (IAA) production.
Abstract: Strains of Bacillus thuringiensis (Bt) are commonly commercialized as bioinoculants for insect pest control, but their benefits go beyond their insecticidal property: they can act as plant growth-promoters. Auxins play a major role in the plant growth promotion. However, the mechanism of auxin production by the Bacilli group, and more specifically by Bt strains, is unclear. In previous work, the plant growth-promoting rhizobacterium (PGPR) B. thuringiensis strain RZ2MS9 increased the corn roots. This drew our attention to the strain's auxin production trait, earlier detected in vitro. Here, we demonstrate that in its genome, RZ2MS9 harbours the complete set of genes required in two pathways that are used for Indole acetic acid (IAA) production. We also detected that the strain produces almost five times more IAA during the stationary phase. The bacterial application increased the shoot dry weight of the Micro-Tom (MT) tomato by 24%. The application also modified MT root architecture, with an increase of 26% in the average lateral root length and inhibition of the axial root. At the cellular level, RZ2MS9-treated MT plants presented elongated root cortical cells with intensified mitotic activity. Altogether, these are the best characterized auxin-associated phenotypes. Besides that, no growth alteration was detected in the auxin-insensitive diageotropic (dgt) plants either with or without the RZ2MS9 inoculation. Our results suggest that auxins play an important role in the ability of B. thuringiensis RZ2MS9 to promote MT growth and provide a better understanding of the auxin production mechanism by a Bt strain.

35 citations


Journal ArticleDOI
TL;DR: Functional evidence is provided that in S. frugiperda these two ABCC transporters serve as receptors of Bt Cry1Fa and Cry1Ab toxins, suggesting a major role of SfABCC2 in the mode of action of these Cry toxins.
Abstract: Background The fall armyworm Spodoptera frugiperda is a major agricultural pest that has invaded the East Hemisphere since 2016, generating a serious threat to food security worldwide including Africa and Asia. The Cry toxins produced by Bacillus thuringiensis (Bt) have been shown to be effective against this insect pest. In different insect ABC transporters (ABCC2 or ABCC3) have been shown to be involved as receptors of some Cry1 toxins. Here we analyzed the role of SfABCC2 and SfABCC3 in the toxicity of Cry1Fa and Cry1Ab toxins in this insect pest. Results Two S. frugiperda SfABCC2 and SfABCC3 knockout strains, coding for potential functional Bt receptors, were created using CRISPR/Cas9 genome editing system. Both knockout strains showed resistance to both Cry1Fa and Cry1Ab toxins compared with the susceptible strain. SfABCC2 knockout strain showed higher resistance to both Cry toxins than SfABCC3 knockout strain, suggesting a major role of SfABCC2 in the mode of action of these Cry toxins. In addition, expression of SfABCC2 and SfABCC3 genes in Trichoplusia ni Hi5 cells also increased the susceptibility to Cry1Ab and Cry1Fa toxins, in agreement with the genome editing results. The double knockout of SfABCC2 and SfABCC3 strain was not viable in contrast to other lepidopteran species. Furthermore, we report here that SfABCC2 or SfABCC3 knockout strains increased their susceptibility to abamectin and spinosad insecticides. Conclusion We provide functional evidence that in S. frugiperda these two ABCC transporters serve as receptors of Bt Cry1Fa and Cry1Ab toxins. © 2020 Society of Chemical Industry.

29 citations


Journal ArticleDOI
19 Feb 2021-PLOS ONE
TL;DR: The hypothesis of an agricultural origin for the Bt contamination is strengthened and calls for further investigations on Bt pesticides.
Abstract: Bacillus thuringiensis (Bt) belongs to the Bacillus cereus (Bc) group, well known as an etiological agent of foodborne outbreaks (FBOs). Bt distinguishes itself from other Bc by its ability to synthesize insecticidal crystals. However, the search for these crystals is not routinely performed in food safety or clinical investigation, and the actual involvement of Bt in the occurrence of FBOs is not known. In the present study, we reveal that Bt was detected in the context of 49 FBOs declared in France between 2007 and 2017. In 19 of these FBOs, Bt was the only microorganism detected, making it the most likely causal agent. Searching for its putative origin of contamination, we noticed that more than 50% of Bt isolates were collected from dishes containing raw vegetables, in particular tomatoes (48%). Moreover, the genomic characterization of isolates showed that most FBO-associated Bt isolates exhibited a quantified genomic proximity to Bt strains, used as biopesticides, especially those from subspecies aizawai and kurstaki. Taken together, these results strengthen the hypothesis of an agricultural origin for the Bt contamination and call for further investigations on Bt pesticides.

28 citations


Journal ArticleDOI
TL;DR: In this paper, a SfABCC2 knockout strain of S. frugiperda was generated using the CRISPR/Cas9 system to provide further functional evidence of the role of this gene in susceptibility and resistance to Cry1F.

27 citations


Journal ArticleDOI
TL;DR: A review of the relevant literature reporting how invertebrates (mainly insects and Caenorhabditis elegans) respond to exposure to B. thuringiensis as either whole bacteria, spores, and/or its pesticidal proteins can be found in this article.
Abstract: SUMMARY Extensive use of chemical insecticides adversely affects both environment and human health. One of the most popular biological pest control alternatives is bioinsecticides based on Bacillus thuringiensis. This entomopathogenic bacterium produces different protein types which are toxic to several insect, mite, and nematode species. Currently, insecticidal proteins belonging to the Cry and Vip3 groups are widely used to control insect pests both in formulated sprays and in transgenic crops. However, the benefits of B. thuringiensis-based products are threatened by insect resistance evolution. Numerous studies have highlighted that mutations in genes coding for surrogate receptors are responsible for conferring resistance to B. thuringiensis. Nevertheless, other mechanisms may also contribute to the reduction of the effectiveness of B. thuringiensis-based products for managing insect pests and even to the acquisition of resistance. Here, we review the relevant literature reporting how invertebrates (mainly insects and Caenorhabditis elegans) respond to exposure to B. thuringiensis as either whole bacteria, spores, and/or its pesticidal proteins.

27 citations


Journal ArticleDOI
TL;DR: In this paper, Bacillus subtilis (AR5) and Bacillus thuringiensis (BR1) were used to inoculate two halophytic plants to alleviate the harmful effects of soil salinity on beans.
Abstract: Salinity is a major problem affecting crop production all over the world. A wide range of adaptation strategies are required to overcome this problem. Endophytic bacteria can build a symbiotic association with their host to improve host plant salt tolerance. In this study, eighteen bacterial endophyte strains were isolated from two native halophytic plants Arthrocnemum macrostachyum and Spergularia marina, and identified as Bacillus, Brevibacillus, Agrobacterium, and Paenibacillus. These endophytic strains exhibit plant growth-promoting activities including phosphate solubilizing, ammonia production, biocontrol of phytopathogen, extracellular enzymatic activities, and indole-3-acetic acid production under normal and salinity stress. A pot experiment was conducted under field conditions to alleviate the harmful effects of soil salinity on bean (Vicia faba L.) by inoculating their seeds with the most potent bacterial isolates Bacillus subtilis (AR5) and Bacillus thuringiensis (BR1). Salinity treatments induced a significant decrease in both growth parameters and metabolic activities, while the activity of antioxidant enzymes and proline content was significantly increased. However, salinity stress induced higher contents of Na+ and decreased contents of N+, P3+, K+, Ca2+, Mg2+, and K+:Na+, it was found that treatment with B. subtilis (AR5) and B. thuringiensis (BR1) individually or in a combination mitigated the effect of salt stress and improved the plant height, shoot dry weights, proline contents, enzymes activities as well enhanced the accumulation of mineral nutrients in shoot plants. Our results concluded that treatment with co-inoculation of B. subtilis (AR5) and B. thuringiensis (BR1) exerted the greatest effect in alleviating the harmful effect of soil salinity stress and can be used as a suitable bio-approach to reclaim salinity-stressed soils.

26 citations


Journal ArticleDOI
05 Feb 2021-Insects
TL;DR: In 2009, the first cases of field-evolved resistance to Bt maize were documented and these cases occurred in Iowa and involved maize that produced Bt toxin Cry3Bb1 as mentioned in this paper.
Abstract: The western corn rootworm, Diabrotica virgifera virgifera LeConte, is among the most serious pests of maize in the United States. Since 2003, transgenic maize that produces insecticidal toxins from the bacterium Bacillus thuringiensis (Bt) has been used to manage western corn rootworm by killing rootworm larvae, which feed on maize roots. In 2009, the first cases of field-evolved resistance to Bt maize were documented. These cases occurred in Iowa and involved maize that produced Bt toxin Cry3Bb1. Since then, resistance has expanded to include other geographies and additional Bt toxins, with some rootworm populations displaying resistance to all commercially available Bt traits. Factors that contributed to field-evolved resistance likely included non-recessive inheritance of resistance, minimal fitness costs of resistance and limited adult dispersal. Additionally, because maize is the primary agricultural crop on which rootworm larvae can survive, continuous maize cultivation, in particular continuous cultivation of Bt maize, appears to be another key factor facilitating resistance evolution. More diversified management of rootworm larvae, including rotating fields out of maize production and using soil-applied insecticide with non-Bt maize, in addition to planting refuges of non-Bt maize, should help to delay the evolution of resistance to current and future transgenic traits.

25 citations


Journal ArticleDOI
TL;DR: It is shown that Bt Cry1Ac protoxin interacts with the gut microbiota to accelerate the mortality of P. xylostella larvae and native gut microbiota can trigger host midgut immune response, which involves the up-regulation of expression of Toll and IMD pathway genes and most antimicrobial peptide genes, respectively.

24 citations


Journal ArticleDOI
TL;DR: In this article, a review of the history and importance of Vip proteins, their types, structure, newly identified specific receptors, and action mechanism of this specific class of proteins are discussed.
Abstract: Bacillus thuringiensis (Bt) bacterium is found in various ecological habitats, and has natural entomo-pesticidal properties, due to the production of crystalline and soluble proteins during different growth phases. In addition to Cry and Cyt proteins, this bacterium also produces Vegetative insecticidal protein (Vip) during its vegetative growth phase, which is considered an excellent toxic candidate because of the difference in sequence homology and receptor sites from Cry proteins. Vip proteins are referred as second-generation insecticidal proteins, which can be used either alone or in complementarity with Cry proteins for the management of various detrimental pests. Among these Vip proteins, Vip1 and Vip2 act as binary toxins and have toxicity toward pests belonging to Hemiptera and Coleoptera orders, whereas the most important Vip3 proteins have insecticidal activity against Lepidopteran pests. These Vip3 proteins are similar to Cry proteins in terms of toxicity potential against susceptible insects. They are reported to be toxic toward pests, which can't be controlled with Cry proteins. The Vip3 proteins have been successfully pyramided along with Cry proteins in transgenic rice, corn, and cotton to combat resistant pest populations. This review provides detailed information about the history and importance of Vip proteins, their types, structure, newly identified specific receptors, and action mechanism of this specific class of proteins. Various studies conducted on Vip proteins all over the world and the current status have been discussed. This review will give insights into the significance of Vip proteins as alternative promising candidate toxic proteins from Bt for the management of pests in most sustainable manner.

22 citations


Journal ArticleDOI
20 May 2021
TL;DR: In this article, the authors investigated the impact of Bacillus thuringiensis as seed treatment and application with silicon on lettuce plants exposed to salinity levels (4 dS m-1 and 8 dSm 1) and found that leaves number, head weight, total yield, RWC, and chlorophyll a, b in stressed lettuce plants were considerably enhanced.
Abstract: We investigated the impact of Bacillus thuringiensis as seed treatment and application with silicon on lettuce plants exposed to salinity levels (4 dS m-1 and 8 dS m-1). Results revealed that leaves number, head weight, total yield, relative water content (RWC), and chlorophyll a and b declined considerably due to two salinity levels. Oxidative stress markers, i.e., hydrogen peroxide (H2O2), superoxide (O2-), and lipid peroxidation (MDA) dramatically augmented in stressed plants. On the other hand, leaves number, total yield, RWC, and chlorophyll a, b in stressed lettuce plants were considerably enhanced because of the application of Si or B. thuringiensis. In contrast, EL%, MDA, and H2O2 were considerably reduced in treated lettuce plants with Si and B. thuringiensis. In addition, the treatment with Si and B. thuringiensis increased head weight (g) and total yield (ton hectare-1), and caused up-regulation of proline and catalase, superoxide dismutase, peroxidase, and polyphenol oxidase activity in lettuce leaves under salinity conditions.

Journal ArticleDOI
TL;DR: In this article, a Bacillus thuringiensis delta-endotoxin, Cry14Ab, was used to control plant-parasitic nematodes in transgenic soybeans.
Abstract: Plant-parasitic nematodes (PPNs) are economically important pests of agricultural crops, and soybean cyst nematode (SCN) in particular is responsible for a large amount of damage to soybean. The need for new solutions for controlling SCN is becoming increasingly urgent, due to the slow decline in effectiveness of the widely used native soybean resistance derived from genetic line PI 88788. Thus, developing transgenic traits for controlling SCN is of great interest. Here, we report a Bacillus thuringiensis delta-endotoxin, Cry14Ab, that controls SCN in transgenic soybean. Experiments in C. elegans suggest the mechanism by which the protein controls nematodes involves damaging the intestine, similar to the mechanism of Cry proteins used to control insects. Plants expressing Cry14Ab show a significant reduction in cyst numbers compared to control plants 30 days after infestation. Field trials also show a reduction in SCN egg counts compared with control plants, demonstrating that this protein has excellent potential to control PPNs in soybean.

Journal ArticleDOI
TL;DR: In recent years, high-yield production has gained importance due to the decrease in agricultural fields in the world and the rapid increase in the population as mentioned in this paper. Cotton is an important source of incom...
Abstract: In recent years, high-yield production has gained importance due to the decrease in agricultural fields in the world and the rapid increase in the population. Cotton is an important source of incom...

Journal ArticleDOI
TL;DR: In this paper, the current status and distribution of the resistance to Cry1A.105 and Cry2Ab2 in H. zea was determined, and the results showed that the resistance appeared to have plateaued, while selection for Cry 2Ab2 resistance is likely still occurring.

Journal ArticleDOI
TL;DR: In this paper, the evolution of resistance to genetically modified Bacillus thuringiensis (Bt) crops in pest populations is a major threat to the sustainability of the technology.
Abstract: Evolution of resistance to genetically modified Bacillus thuringiensis (Bt) crops in pest populations is a major threat to the sustainability of the technology. Incidents of field resistance that h...

Journal ArticleDOI
15 Jan 2021-Toxins
TL;DR: In this article, the current status and distribution of the Cry1Ab resistance, and evaluate the susceptibility to Vip3Aa20 expressed in MIR 162 corn in H. zea in the southeastern U.S.
Abstract: The corn earworm, Helicoverpa zea (Boddie), is a major pest targeted by pyramided Bacillus thuringiensis (Bt) corn and cotton in the U.S. Cry1Ab is one of the first insecticidal toxins used in Bt crops, while Vip3A is a relatively new toxin that has recently been incorporated into Cry corn with event MIR 162 and Cry cotton varieties to generate pyramided Bt traits targeting lepidopteran pests including H. zea. The objectives of this study were to determine the current status and distribution of the Cry1Ab resistance, and evaluate the susceptibility to Vip3Aa20 expressed in MIR 162 corn in H. zea in the southeastern U.S. During 2018 and 2019, 32 H. zea populations were collected from non-Bt corn (19 populations), Cry corn (12), and Cry/Vip3A cotton (1) across major corn areas in seven southeastern states of the U.S. Susceptibility of these populations to Cry1Ab and Vip3Aa20 was determined using diet-overlay bioassays. Compared to a known susceptible insect strain, 80% of the field populations were 13- to >150-fold resistant to Cry1Ab, while their response to Vip3Aa20 ranged from >11-fold more susceptible to 9-fold more tolerant. Mean susceptibility to each Bt toxin was not significantly different between the two groups of the populations collected from non-Bt and Bt crops, as well as between the two groups of the populations collected during 2018 and 2019. The results show that resistance to Cry1Ab in H. zea is widely distributed across the region. However, the Cry1Ab-resistant populations are not cross-resistant to Vip3Aa20, and H. zea in the region is still susceptible to the Vip3Aa20 toxin. Vip3Aa20 concentrations between 5 and 10 µg/cm2 may be used as diagnostic concentrations for susceptibility monitoring in future. Additional studies are necessary to elucidate the impact of the selection with Bt corn on resistance evolution in H. zea to Vip3A cotton in the U.S.

Journal ArticleDOI
Sathi Paul1, Sampa Das1
01 Apr 2021-Nucleus
TL;DR: This review demonstrates the insecticidal potential of some candidate proteins and their possible mode of action by identifying their target molecules in insects’ tissue and provides an overview of the applicability of these proteins in crop protection.
Abstract: Insect predation problem in agriculture and forestry has challenged researchers worldwide to identify newer eco-friendly insecticides. Among them Bacillus thuringiensis δ-endotoxin (Bt) has been the most widely used commercial insecticide till date. The advantages of Bt as a “green” insecticide are its high specificity to target insects (it is nontoxic to mammals, birds and even to most beneficial insects) and the slow rate of development of resistance against it by insects. This toxin used either in the form of bio formulations or through its expression in crop plants, is found to be sensitive against insect pests belonging to the family Lepidoptera, Coleoptera and Diptera. However, the sap sucking homopteran group of insects generally remain insensitive to Bt toxin and show susceptibility to various plant lectins when fed with artificial diet or through expression in transgenic plants. This review demonstrates the insecticidal potential of some candidate proteins and their possible mode of action by identifying their target molecules in insects’ tissue. We also provide an overview of the applicability of these proteins in crop protection.

Journal ArticleDOI
TL;DR: In this article, the Vip3 proteins are proposed to exert their insecticidal activity through pore formation, though to date there is no mechanistic description of how this occurs on the membrane.
Abstract: Insect pests are a major cause of crop losses worldwide, with an estimated economic cost of $470 billion annually. Biotechnological tools have been introduced to control such insects without the need for chemical pesticides; for instance, the development of transgenic plants harbouring genes encoding insecticidal proteins. The Vip3 (vegetative insecticidal protein 3) family proteins from Bacillus thuringiensis convey toxicity to species within the Lepidoptera, and have wide potential applications in commercial agriculture. Vip3 proteins are proposed to exert their insecticidal activity through pore formation, though to date there is no mechanistic description of how this occurs on the membrane. Here we present cryo-EM structures of a Vip3 family toxin in both inactive and activated forms in conjunction with structural and functional data on toxin-membrane interactions. Together these data demonstrate that activated Vip3Bc1 complex is able to insert into membranes in a highly efficient manner, indicating that receptor binding is the likely driver of Vip3 specificity.

Journal ArticleDOI
TL;DR: In this paper, a new approach was employed aiming at the use of Bacillus thyrus for the biodegradation of pyrethroids, and the results showed promising results.
Abstract: The microbial diversity of several environments has been explored by researchers for the biodegradation of pyrethroids. In this study, a new approach was employed aiming at the use of Bacillus thur...

Journal ArticleDOI
TL;DR: In this article, the authors used CRISPR/Cas9 gene editing to test the hypothesis that mutations in the pink bollworm gene encoding ABCA2 (PgABCA2) can cause resistance to Cry2Ab.
Abstract: Crops genetically engineered to produce insecticidal proteins from Bacillus thuringiensis (Bt) have many benefits and are important globally for managing insect pests. However, the evolution of pest resistance to Bt crops reduces their benefits. Understanding the genetic basis of such resistance is needed to better monitor, manage, and counter pest resistance to Bt crops. Previous work shows that resistance to Bt toxin Cry2Ab is associated with mutations in the gene encoding the ATP-binding cassette protein ABCA2 in lab- and field-selected populations of the pink bollworm (Pectinophora gossypiella), one of the world’s most destructive pests of cotton. Here we used CRISPR/Cas9 gene editing to test the hypothesis that mutations in the pink bollworm gene encoding ABCA2 (PgABCA2) can cause resistance to Cry2Ab. Consistent with this hypothesis, introduction of disruptive mutations in PgABCA2 in a susceptible strain of pink bollworm increased the frequency of resistance to Cry2Ab and facilitated creation of a Cry2Ab-resistant strain. All Cry2Ab-resistant individuals tested in this study had disruptive mutations in PgABCA2. Overall, we found 17 different disruptive mutations in PgABCA2 gDNA and 26 in PgABCA2 cDNA, including novel mutations corresponding precisely to single-guide (sgRNA) sites used for CRISPR/Cas9. Together with previous results, these findings provide the first case of practical resistance to Cry2Ab where evidence identifies a specific gene in which disruptive mutations can cause resistance and are associated with resistance in field-selected populations.

Journal ArticleDOI
TL;DR: Results demonstrate that proteins from B. laterosporus are as efficacious as the well-known Bacillus thuringiensis insecticidal proteins in controlling major insect pests such as WCR.
Abstract: This study describes three closely related proteins, cloned from Brevibacillus laterosporus strains, that are lethal upon feeding to Diabrotica virgifera virgifera LeConte, the western corn rootworm (WCR). Mpp75Aa1, Mpp75Aa2 and Mpp75Aa3 were toxic to WCR larvae when fed purified protein. Transgenic plants expressing each mMpp75Aa protein were protected from feeding damage and showed significant reduction in adult emergence from infested plants by both susceptible and Cry3Bb1 and Cry34Ab1/Cry35Ab1-resistant WCR. These results demonstrate that proteins from B. laterosporus are as efficacious as the well-known Bacillus thuringiensis (Bt) insecticidal proteins in controlling major insect pests such as WCR. The deployment of transgenic maize expressing mMpp75Aa along with other active molecules lacking cross-resistance have the potential to be a useful tool for control of WCR populations resistant to current Bt traits.IMPORTANCE Insects feeding on roots of crops can damage the plant roots resulting in yield loss due to poor water and nutrient uptake and plant lodging. In maize the western corn rootworm (WCR) can cause severe damage to the roots resulting in significant economic loss for farmers. Genetically modified (GM) expressing Bacillus thuringiensis (Bt) insect control proteins, has provided a solution for control of these pests. In recent years populations of WCR resistant to the Bt proteins in commercial GM maize have emerged. There is a need to develop new insecticidal traits for the control of WCR populations resistant to current commercial traits. New proteins with commercial level efficacy on WCR from sources other than Bt are becoming more critical. The Mpp75Aa proteins, from B. laterosporus, when expressed in maize, are efficacious against the resistant populations of WCR and have the potential to provide solutions for control of resistant WCR.

Journal ArticleDOI
24 Mar 2021-PLOS ONE
TL;DR: In this paper, the effects of Bacillus thuringiensis var. tenebrionis (morrissoni) (Bt), a natural complex of avermectins and a combination of both agents were investigated in the Colorado potato beetle Leptinotarsa decemlineata.
Abstract: Gut physiology and the bacterial community play crucial roles in insect susceptibility to infections and insecticides. Interactions among Colorado potato beetle Leptinotarsa decemlineata (Say), its bacterial associates, pathogens and xenobiotics have been insufficiently studied. In this paper, we present our study of the survival, midgut histopathology, activity of digestive enzymes and bacterial communities of L. decemlineata larvae under the influence of Bacillus thuringiensis var. tenebrionis (morrissoni) (Bt), a natural complex of avermectins and a combination of both agents. Moreover, we estimated the impact of culturable enterobacteria on the susceptibility of the larvae to Bt and avermectins. An additive effect between Bt and avermectins was established regarding the mortality of the larvae. Both agents led to the destruction of midgut tissues, a decrease in the activity of alpha-amylases and alkaline proteinases, a decrease in the Spiroplasma leptinotarsae relative abundance and a strong elevation of Enterobacteriaceae abundance in the midgut. Moreover, an elevation of the enterobacterial CFU count was observed under the influence of Bt and avermectins, and the greatest enhancement was observed after combined treatment. Insects pretreated with antibiotics were less susceptible to Bt and avermectins, but reintroduction of the predominant enterobacteria Enterobacter ludwigii, Citrobacter freundii and Serratia marcescens increased susceptibility to both agents. We suggest that enterobacteria play an important role in the acceleration of Bt infection and avermectin toxicoses in L. decemlineata and that the additive effect between Bt and avermectin may be mediated by alterations in the bacterial community.

Journal ArticleDOI
02 Sep 2021-Toxins
TL;DR: In this article, the authors evaluated H. zea resistance to Vip3Aa using diet bioassays to test 42,218 larvae from three lab strains and 71 strains derived from the field during 2016 to 2020 in Arkansas, Louisiana, Mississippi, Tennessee, and Texas.
Abstract: Evolution of resistance by pests can reduce the benefits of crops genetically engineered to produce insecticidal proteins from Bacillus thuringiensis (Bt). Because of the widespread resistance of Helicoverpa zea to crystalline (Cry) Bt toxins in the United States, the vegetative insecticidal protein Vip3Aa is the only Bt toxin produced by Bt corn and cotton that remains effective against some populations of this polyphagous lepidopteran pest. Here we evaluated H. zea resistance to Vip3Aa using diet bioassays to test 42,218 larvae from three lab strains and 71 strains derived from the field during 2016 to 2020 in Arkansas, Louisiana, Mississippi, Tennessee, and Texas. Relative to the least susceptible of the three lab strains tested (BZ), susceptibility to Vip3Aa of the field-derived strains decreased significantly from 2016 to 2020. Relative to another lab strain (TM), 7 of 16 strains derived from the field in 2019 were significantly resistant to Vip3Aa, with up to 13-fold resistance. Susceptibility to Vip3Aa was significantly lower for strains derived from Vip3Aa plants than non-Vip3Aa plants, providing direct evidence of resistance evolving in response to selection by Vip3Aa plants in the field. Together with previously reported data, the results here convey an early warning of field-evolved resistance to Vip3Aa in H. zea that supports calls for urgent action to preserve the efficacy of this toxin.

Journal ArticleDOI
TL;DR: In this article, a resurgence of the cosmopolitan bollworm Helicoverpa armigera following a contraction of Bt cotton area in dynamic agro-landscapes over 2007-2019 in North China Plain.
Abstract: Genetically-modified crops expressing Bacillus thuringiensis (Bt) proteins have been widely cultivated, permitting an effective non-chemical control of major agricultural pests. While their establishment can enable an area-wide suppression of polyphagous herbivores, no information is available on the impact of Bt crop abandonment in entire landscape matrices. Here, we detail a resurgence of the cosmopolitan bollworm Helicoverpa armigera following a contraction of Bt cotton area in dynamic agro-landscapes over 2007-2019 in North China Plain. An 80% reduction in Bt cotton was mirrored in a 1.9-fold increase of ambient H. armigera population levels, culminating in 1.5-2.1-fold higher yield loss and a 2.0-4.4-fold increase in pesticide use frequency in non-Bt crops (i.e. maize, peanut, soybean). Our work unveils the fate of herbivorous insect populations following a progressive dis-use of insecticidal crop cultivars, and hints at how tactically deployed Bt crops could be paired with agro-ecological measures to mitigate the environmental footprint of crop production.

Journal ArticleDOI
16 May 2021-Toxins
TL;DR: In this article, the authors investigated the effects of Bt-based pesticides on non-target organisms and found that exposure to Bt treatment may affect nontarget organisms by reducing prey base and its nutritional value, resulting in delayed alleviation of their viability.
Abstract: Bacillus thuringiensis (Bt), a natural pathogen of different invertebrates, primarily insects, is widely used as a biological control agent. While Bt-based preparations are claimed to be safe for non-target organisms due to the immense host specificity of the bacterium, the growing evidence witnesses the distant consequences of their application for natural communities. For instance, upon introduction to soil habitats, Bt strains can affect indigenous microorganisms, such as bacteria and fungi, and further establish complex relationships with local plants, ranging from a mostly beneficial demeanor, to pathogenesis-like plant colonization. By exerting a direct effect on target insects, Bt can indirectly affect other organisms in the food chain. Furthermore, they can also exert an off-target activity on various soil and terrestrial invertebrates, and the frequent acquisition of virulence factors unrelated to major insecticidal toxins can extend the Bt host range to vertebrates, including humans. Even in the absence of direct detrimental effects, the exposure to Bt treatment may affect non-target organisms by reducing prey base and its nutritional value, resulting in delayed alleviation of their viability. The immense phenotypic plasticity of Bt strains, coupled with the complexity of ecological relationships they can engage in, indicates that further assessment of future Bt-based pesticides’ safety should consider multiple levels of ecosystem organization and extend to a wide variety of their inhabitants.

Journal ArticleDOI
TL;DR: The findings suggest that the first generation Bt corn expressing single Cry1 toxin should not be the first choice because of the potential risk of control failure or less efficacy against H. armigera, A. ypsilon or M. separate.
Abstract: Transgenic crops that produce Bacillus thuringiensis (Bt) toxins are effective tools for controlling lepidopteran pests. However, the degree of susceptibility to Bt toxins differs among various pest species due to relatively narrow spectrum and high selectivity of such toxins. Bt corn hybrids for Chinese market were designed to target Asian corn borer Ostrinia furnacalis (Guenee), while their efficacy against other lepidopteran pests are not well defined, such as Conogethes punctiferalis (Guenee), Helicoverpa armigera (Hubner), Agrotis ypsilon (Rottemberg), and Mythimna separata (Walker), which are also important lepidopteran pests on corn in the Huang-Huai-Hai Summer Corn Region of China. To determine what type of Bt corn is suitable for this region, the efficacy of five Bt toxins, i.e., Cry1Ab, Cry1Ac, Cry1F, Cry2Ab, and Vip3A, to these five lepidopteran species was evaluated in laboratory. Both O. furnacalis and C. punctiferalis showed similar high susceptibility to all five Bt toxins. A. ypsilon and M. separate were less sensitive to Cry1Ab and Cry1Ac than the other species. H. armigera, A. ypsilon and M. separate were less sensitive to Cry1F than O. furnacalis and C. punctiferalis. H. armigera was more sensitive to Cry2Ab than other tested species. All five species were equally sensitive to Vip3A, though their LC50s were all relatively higher. These findings suggest that the first generation Bt corn expressing single Cry1 toxin should not be the first choice because of the potential risk of control failure or less efficacy against H. armigera, A. ypsilon or M. separate. The second-generation Bt corn expressing Cry1 and Cry2 toxins, or the third generation Bt corn expressing Cry1, Cry2 and Vip3A toxins might produce better protection of corn in the Huang-Huai-Hai Summer Corn Region of China.

Journal ArticleDOI
TL;DR: The use of Bacillus thuringiensis (Bt) as a biocontrol agent against insect pest for sustainable agriculture has been discussed in this article, where the authors explore the potential as plant growth-promoting potential and solubilization of minerals and the uses as a bio-fertilizer.
Abstract: Bacillus thuringiensis (Bt) has been used in agriculture for a long time because of its insecticidal proteins which make it a valuable environment-friendly biopesticide. However, its use is not only limited to insecticidal properties. Current and previous studies indicate its potential as a biofertilizer for promoting plant growth, the development of transgenic plants, and others. It is the presence of δ-endotoxins, especially cry protein, which attributes the insecticidal property to the bacteria. Besides, there are some vegetative and secreted insecticidal proteins that exert their toxic activity towards specific species. The present review briefly provides an overview of the Bt uses and application as a biocontrol agent against insect pest for sustainable agriculture. Historical development of Bt as biocontrol, classification of various cry proteins, their mechanisms of actions against different insect-pest, and incorporation of cry genes in the plant for developing transgenic Bt plants such as Bt cotton, potato, and maize. Applications of Bt as biofertilizer and the various bioformulations as biopesticide are also described. Uses of harmful pesticides and chemical cause various health issues and environmental problem; therefore, the Bt served as the best alternative to overcome the above issue. Also, we aim to explore the potential as plant growth-promoting potential and solubilization of minerals and the uses as a biofertilizer, keeping the high specificity and environmental safety of Bt. Its various formulations are commercially available and considered an efficient alternative to chemical pesticides.

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TL;DR: In this article, the effect of HaABCC2 and HaCAD transporters genes on Bacillus thuringiensis Cry toxins used in insect-pest control was investigated.

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TL;DR: In this paper, the authors reveal that a transcription factor PxJun activated by the MAPK signaling pathway can suppress PxABCB1 expression and confers Cry1Ac resistance in P. xylostella.
Abstract: Deciphering the molecular mechanisms underlying insect resistance to Cry toxins produced by Bacillus thuringiensis (Bt) is pivotal for the sustainable utilization of Bt biopesticides and transgenic Bt crops. Previously, we identified that mitogen-activated protein kinase (MAPK)-mediated reduced expression of the PxABCB1 gene is associated with Bt Cry1Ac resistance in the diamondback moth, Plutella xylostella (L.). However, the underlying transcriptional regulation mechanism remains enigmatic. Here, the PxABCB1 promoter in Cry1Ac-susceptible and Cry1Ac-resistant P. xylostella strains was cloned and analyzed and found to contain a putative Jun binding site (JBS). A dual-luciferase reporter assay and yeast one-hybrid assay demonstrated that the transcription factor PxJun repressed PxABCB1 expression by interacting with this JBS. The expression levels of PxJun were increased in the midguts of all resistant strains compared to the susceptible strain. Silencing of PxJun expression significantly elevated PxABCB1 expression and Cry1Ac susceptibility in the resistant NIL-R strain, and silencing of PxMAP4K4 expression decreased PxJun expression and also increased PxABCB1 expression. These results indicate that MAPK-activated PxJun suppresses PxABCB1 expression to confer Cry1Ac resistance in P. xylostella, deepening our understanding of the transcriptional regulation of midgut Cry receptor genes and the molecular basis of insect resistance to Bt Cry toxins. IMPORTANCE The transcriptional regulation mechanisms underlying reduced expression of Bt toxin receptor genes in Bt-resistant insects remain elusive. This study unveils that a transcription factor PxJun activated by the MAPK signaling pathway represses PxABCB1 expression and confers Cry1Ac resistance in P. xylostella. Our results provide new insights into the transcriptional regulation mechanisms of midgut Cry receptor genes and deepen our understanding of the molecular basis of insect resistance to Bt Cry toxins. To our knowledge, this study identified the first transcription factor that can be involved in the transcriptional regulation mechanisms of midgut Cry receptor genes in Bt-resistant insects.

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TL;DR: In this article, the authors characterized the associated bacterial communities of Bt-resistant and -susceptible western corn rootworms, a widespread pest of maize in the United States, and found resistant insects harbor a bacterial community that is less rich and distinct from susceptible insects.
Abstract: Evolution of resistance to transgenic crops producing toxins from Bacillus thuringiensis (Bt) threatens the sustainability of the technology. Examination of resistance mechanisms has largely focused on characterization of mutations in proteins serving as Bt toxin binding sites. However, insect microbial communities have the potential to provide host resistance to pesticides in a myriad of ways. Previous findings suggest the killing mechanism of Bt relies on enteric bacteria becoming pathogenic in the disrupted gut environment of the insect following Bt intoxication. Thus, here we hypothesized that resistance to Bt would alter the microbiome composition of the insect. Previous studies have manipulated the microbiome of susceptible insects and monitored their response to Bt. In our study, we characterized the associated bacterial communities of Bt-resistant and -susceptible western corn rootworms, a widespread pest of maize in the United States. We found resistant insects harbor a bacterial community that is less rich and distinct from susceptible insects. After feeding on Bt-expressing maize, susceptible insects exhibited dysbiosis of the associated bacterial community, whereas the community within resistant insects remained relatively unchanged. These results suggest resistance to Bt produces alterations in the microbiome of the western corn rootworm that may contribute to resistance. We further demonstrated that by itself, feeding on Bt toxin-expressing seedlings caused a shift in the microbiota. This work provides a broader picture of the effect stressors have on microbiome composition, and the potential heritable changes induced as a result of intense selection.