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Insecticidal Toxins from Bacillus thuringiensis
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Insecticidal Toxins from Bacillus thuringiensis

A special issue of Toxins (ISSN 2072-6651). This special issue belongs to the section "Bacterial Toxins".

Deadline for manuscript submissions: closed (28 February 2019) | Viewed by 64598

Special Issue Editor

Prof. Dr. Alejandra Bravo

E-Mail Website
Guest Editor
Instituto de Biotecnología, Universidad Nacional Autónoma de México, Cuernavaca 62250, Mexico
Interests: Bacillus thuringiensis; Cry toxins; Vip3A toxins; pore formation; toxin receptors; resistance mechanisms; Cyt toxin
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Bacillus thuringiensis (Bt) belongs to the Bacillus cereus sensu lato group that also includes other six closely-related species: B. cereus sensu stricto, B. anthracis, B. weihenstephanensis, B. cytotoxicus, B. mycoides and B. pseudomycoides. The feature that distinguishes Bt from the other members of the Bacillus cereus group is its entomopathogenic properties. Bt produces insecticidal-endotoxin proteins (Cry and Cyt) during sporulation phase as parasporal crystals and also Vip toxins during vegetative phase of growth. Different proteins not related phylogenetically comprise the Cry family. Among these, the 3-Domain Cry toxins (3d-Cry), binary Cry toxins (Bin-Cry) and Mtx toxins (Mtx-Cry) showed insecticidal properties. In addition, novel insecticidal proteins have been described in other organisms. The aim of this Special Issue is to offer an overview of the current knowledge about all these families of proteins produced by Bt and other organisms, and discuss how evolution of these protein families create such a diverse arsenal of toxins. Review and research articles about their structures and the novel insights in the understanding of their mechanism of action will be welcome. One of the major concerns regarding the use of Bt is the generation of insect populations resistant to these toxins, studies focused to understand the resistance mechanisms and the proposed strategies and rational procedures to cope with resistance to these toxins are also welcome.

Prof. Dr. Alejandra Bravo
Guest Editor

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Keywords

  • Bacillus thuringiensis
  • Cry toxins
  • Vip toxins
  • Cyt toxins
  • Bin toxins
  • Mtx toxins
  • insecticidal proteins
  • insect resistance

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Published Papers (15 papers)

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Research

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18 pages, 3319 KiB  
Article
The Cadherin Cry1Ac Binding-Region is Necessary for the Cooperative Effect with ABCC2 Transporter Enhancing Insecticidal Activity of Bacillus thuringiensis Cry1Ac Toxin
by Yuemin Ma, Jianfeng Zhang, Yutao Xiao, Yanchao Yang, Chenxi Liu, Rong Peng, Yongbo Yang, Alejandra Bravo, Mario Soberón and Kaiyu Liu
Toxins 2019, 11(9), 538; https://doi.org/10.3390/toxins11090538 - 14 Sep 2019
Cited by 21 | Viewed by 4312
Abstract
Bacillus thuringiensis Cry1Ac toxin binds to midgut proteins, as cadherin (CAD) and ABCC2 transporter, to form pores leading to larval death. In cell lines, co-expression of CAD and ABCC2 enhance Cry1Ac toxicity significantly, but the mechanism remains elusive. Here, we show that the [...] Read more.
Bacillus thuringiensis Cry1Ac toxin binds to midgut proteins, as cadherin (CAD) and ABCC2 transporter, to form pores leading to larval death. In cell lines, co-expression of CAD and ABCC2 enhance Cry1Ac toxicity significantly, but the mechanism remains elusive. Here, we show that the expression of Helicoverpa armigera CAD (HaCAD-GFP) in Hi5 cells induces susceptibility to Cry1Ac and enhanced Cry1Ac toxicity when co-expressed with H. armigera ABCC2 (HaABCC2-GFP), since Cry1Ac toxicity increased 735-fold compared to Hi5 cells expressing HaCAD-GFP alone or 28-fold compared to HaABCC2-GFP alone. In contrast, the expression of the Spodoptera litura CAD (SlCAD-GFP) in Hi5 cells did not induce susceptibility to Cry1Ac nor it potentiated Cry1Ac toxicity with HaABCC2-GFP. To identify the CAD regions involved in the enhancement of Cry1Ac toxicity with ABCC2, the different CAD domains were replaced between SlCAD-GFP and HaCad-GFP proteins, and cytotoxicity assays were performed in Hi5 cells in the absence or presence of HaABCC2-GFP. The HaCAD toxin-binding region (TB), specifically the CAD repeat-11, was necessary to enhance Cry1Ac toxicity with ABCC2. We propose that CAD TB is involved in recruiting Cry1Ac to localize it in a good position for its interaction with the ABCC2, resulting in efficient toxin membrane insertion enhancing Cry1Ac toxicity. Full article
(This article belongs to the Special Issue Insecticidal Toxins from Bacillus thuringiensis)
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13 pages, 1871 KiB  
Article
Pink Bollworm Resistance to Bt Toxin Cry1Ac Associated with an Insertion in Cadherin Exon 20
by Ling Wang, Yuemin Ma, Xueqin Guo, Peng Wan, Kaiyu Liu, Shengbo Cong, Jintao Wang, Dong Xu, Yutao Xiao, Xianchun Li, Bruce E. Tabashnik and Kongming Wu
Toxins 2019, 11(4), 186; https://doi.org/10.3390/toxins11040186 - 28 Mar 2019
Cited by 27 | Viewed by 4327
Abstract
Insecticidal proteins from Bacillus thuringiensis (Bt) are widely used to control insect pests, but their efficacy is reduced when pests evolve resistance. We report on a novel allele (r16) of the cadherin gene (PgCad1) in pink bollworm (Pectinophora [...] Read more.
Insecticidal proteins from Bacillus thuringiensis (Bt) are widely used to control insect pests, but their efficacy is reduced when pests evolve resistance. We report on a novel allele (r16) of the cadherin gene (PgCad1) in pink bollworm (Pectinophora gossypiella) associated with resistance to Bt toxin Cry1Ac, which is produced by transgenic cotton. The r16 allele isolated from a field population in China has 1545 base pairs of a degenerate transposon inserted in exon 20 of PgCad1, which generates a mis-spliced transcript containing a premature stop codon. A strain homozygous for r16 had 300-fold resistance to Cry1Ac, 2.6-fold cross-resistance to Cry2Ab, and completed its life cycle on transgenic Bt cotton producing Cry1Ac. Inheritance of Cry1Ac resistance was recessive and tightly linked with r16. Compared with transfected insect cells expressing wild-type PgCad1, cells expressing r16 were less susceptible to Cry1Ac. Recombinant cadherin protein was transported to the cell membrane in cells transfected with the wild-type PgCad1 allele, but not in cells transfected with r16. Cadherin occurred on brush border membrane vesicles (BBMVs) in the midgut of susceptible larvae, but not resistant larvae. These results imply that the r16 allele mediates Cry1Ac resistance in pink bollworm by interfering with the localization of cadherin. Full article
(This article belongs to the Special Issue Insecticidal Toxins from Bacillus thuringiensis)
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13 pages, 4878 KiB  
Article
The Spodoptera exigua ABCC2 Acts as a Cry1A Receptor Independently of its Nucleotide Binding Domain II
by Daniel Pinos, María Martínez-Solís, Salvador Herrero, Juan Ferré and Patricia Hernández-Martínez
Toxins 2019, 11(3), 172; https://doi.org/10.3390/toxins11030172 - 22 Mar 2019
Cited by 18 | Viewed by 4251
Abstract
ABC proteins are primary-active transporters that require the binding and hydrolysis of ATP to transport substrates across the membrane. Since the first report of an ABCC2 transporter as receptor of Cry1A toxins, the number of ABC transporters known to be involved in the [...] Read more.
ABC proteins are primary-active transporters that require the binding and hydrolysis of ATP to transport substrates across the membrane. Since the first report of an ABCC2 transporter as receptor of Cry1A toxins, the number of ABC transporters known to be involved in the mode of action of Cry toxins has increased. In Spodoptera exigua, a mutation in the SeABCC2 gene is described as genetically linked to resistance to the Bt-product XentariTM. This mutation affects an intracellular domain involved in ATP binding, but not the extracellular loops. We analyzed whether this mutation affects the role of the SeABCC2 as a functional receptor to Cry1A toxins. The results show that Sf21 cells expressing the truncated form of the transporter were susceptible to Cry1A toxins. Moreover, specific Cry1Ac binding was observed in those cells expressing the truncated SeABCC2. Additionally, no differences in the irreversible Cry1Ac binding component (associated with the toxin insertion into the membrane) were observed when tested in Sf21 cells expressing either the full-length or the truncated form of the SeABCC2 transporter. Therefore, our results point out that the partial lack of the nucleotide binding domain II in the truncated transporter does not affect its functionality as a Cry1A receptor. Full article
(This article belongs to the Special Issue Insecticidal Toxins from Bacillus thuringiensis)
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18 pages, 2882 KiB  
Article
Engineering of Bacillus thuringiensis Cry Proteins to Enhance the Activity against Western Corn Rootworm
by Jingtong Hou, Ruth Cong, Michi Izumi-Willcoxon, Hana Ali, Yi Zheng, Ericka Bermudez, Mark McDonald, Mark Nelson and Takashi Yamamoto
Toxins 2019, 11(3), 162; https://doi.org/10.3390/toxins11030162 - 14 Mar 2019
Cited by 13 | Viewed by 4069
Abstract
A novel Bacillus thuringiensis Cry protein, Cry8Hb, active against Diabrotica virgifera virgifera (Western corn rootworm, WCRW) was discovered. Unexpectedly, the anti-rootworm activity of the Cry8Hb toxin was enhanced significantly by fusing Escherichia coli maltose binding protein (MBP) to this Cry toxin. While the [...] Read more.
A novel Bacillus thuringiensis Cry protein, Cry8Hb, active against Diabrotica virgifera virgifera (Western corn rootworm, WCRW) was discovered. Unexpectedly, the anti-rootworm activity of the Cry8Hb toxin was enhanced significantly by fusing Escherichia coli maltose binding protein (MBP) to this Cry toxin. While the exact mechanism of the activity enhancement remains indefinite, it is probable that the enhancement is a result of increased solubility of the MBP-Cry8Hb fusion in the rootworm midgut. This hypothesis was examined using a synthetic Cry3 protein called IP3-1, which was not soluble at a neutral pH like Cry8Hb and marginally active to WCRW. When IP3-1 was fused to MBP, its anti-WCRW activity was enhanced 13-fold. To further test the hypothesis, DNA shuffling was performed on IP3-1 to increase the solubility without MBP. Screening of shuffled libraries found six new IP3 variants showing very high anti-WCRW activity without MBP. Sequence and 3D structure analysis of those highly active, shuffled IP3 variants revealed several charge-altering mutations such as Lys to Glu on the putative MBP-attaching side of the IP3 molecule. It is likely that those mutations make the protein acidic to substitute the functions of MBP including enhancing the solubility of IP3 at a neutral pH. Full article
(This article belongs to the Special Issue Insecticidal Toxins from Bacillus thuringiensis)
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14 pages, 3190 KiB  
Article
Molecular Interaction-Based Exploration of the Broad Spectrum Efficacy of a Bacillus thuringiensis Insecticidal Chimeric Protein, Cry1AcF
by Maniraj Rathinam, Karthik Kesiraju, Shweta Singh, Vinutha Thimmegowda, Vandna Rai, Debasis Pattanayak and Rohini Sreevathsa
Toxins 2019, 11(3), 143; https://doi.org/10.3390/toxins11030143 - 02 Mar 2019
Cited by 11 | Viewed by 3530
Abstract
Bacillus thuringiensis insecticidal proteins (Bt ICPs) are reliable and valuable options for pest management in crops. Protein engineering of Bt ICPs is a competitive alternative for resistance management in insects. The primary focus of the study was to reiterate the translational utility [...] Read more.
Bacillus thuringiensis insecticidal proteins (Bt ICPs) are reliable and valuable options for pest management in crops. Protein engineering of Bt ICPs is a competitive alternative for resistance management in insects. The primary focus of the study was to reiterate the translational utility of a protein-engineered chimeric Cry toxin, Cry1AcF, for its broad spectrum insecticidal efficacy using molecular modeling and docking studies. In-depth bioinformatic analysis was undertaken for structure prediction of the Cry toxin as the ligand and aminopeptidase1 receptors (APN1) from Helicoverpa armigera (HaAPN1) and Spodoptera litura (SlAPN1) as receptors, followed by interaction studies using protein-protein docking tools. The study revealed feasible interactions between the toxin and the two receptors through H-bonding and hydrophobic interactions. Further, molecular dynamics simulations substantiated the stability of the interactions, proving the broad spectrum efficacy of Cry1AcF in controlling H. armigera and S. litura. These findings justify the utility of protein-engineered toxins in pest management. Full article
(This article belongs to the Special Issue Insecticidal Toxins from Bacillus thuringiensis)
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13 pages, 1880 KiB  
Article
Occurrence and Ear Damage of Helicoverpa zea on Transgenic Bacillus thuringiensis Maize in the Field in Texas, U.S. and Its Susceptibility to Vip3A Protein
by Fei Yang, José C. Santiago González, Jayme Williams, Donald C. Cook, Ryan T. Gilreath and David L. Kerns
Toxins 2019, 11(2), 102; https://doi.org/10.3390/toxins11020102 - 09 Feb 2019
Cited by 67 | Viewed by 4721
Abstract
The corn earworm, Helicoverpa zea (Boddie), is a major pest of Bacillus thuringiensis (Bt) maize and cotton in the U.S. Reduced efficacy of Bt plants expressing Cry1 and Cry2 against H. zea has been reported in some areas of the U.S. In this [...] Read more.
The corn earworm, Helicoverpa zea (Boddie), is a major pest of Bacillus thuringiensis (Bt) maize and cotton in the U.S. Reduced efficacy of Bt plants expressing Cry1 and Cry2 against H. zea has been reported in some areas of the U.S. In this study, we evaluated the occurrence and ear damage of H. zea on transgenic Bt maize expressing Cry proteins or a combination of Vip3A and Cry proteins in the field in Texas in 2018. We found that the occurrence of H. zea larvae and the viable kernel damage area on the ear were not different between non-Bt maize and Bt maize expressing Cry1A.105+Cry2Ab2 and Cry1Ab+Cry1F proteins. A total of 67.5% of the pyramided Bt maize expressing Cry1Ab+Cry1F+Vip3A was damaged by 2nd–4th instar larvae of H. zea. Diet bioassays showed that the resistance ratio against Vip3Aa51 for H. zea obtained from Cry1Ab+Cry1F+Vip3A maize was 20.4 compared to a field population collected from Cry1F+Cry1A.105+Cry2Ab2 maize. Leaf tissue bioassays showed that 7-day survivorship on WideStrike3 (Cry1F+Cry1Ac+Vip3A) cotton leaves was significantly higher for the H. zea population collected from Cry1Ab+Cry1F+Vip3A maize than for a Bt-susceptible laboratory population. The results generated from this study suggest that H. zea has evolved practical resistance to Cry1 and Cry2 proteins. Therefore, it is crucial to ensure the sustainable use of the Vip3A technology in Bt maize and cotton. Full article
(This article belongs to the Special Issue Insecticidal Toxins from Bacillus thuringiensis)
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14 pages, 1281 KiB  
Article
Comparative Proteomics of Peritrophic Matrix Provides an Insight into its Role in Cry1Ac Resistance of Cotton Bollworm Helicoverpa armigera
by Minghui Jin, Chongyu Liao, Swapan Chakrabarty, Kongming Wu and Yutao Xiao
Toxins 2019, 11(2), 92; https://doi.org/10.3390/toxins11020092 - 02 Feb 2019
Cited by 14 | Viewed by 3731
Abstract
Crystalline (Cry) proteins from Bacillus thuringiensis (Bt) are widely used in sprays and transgenic crops to control insect pests, but the evolution of insect resistance threatens their long-term use. Different resistance mechanisms have been identified, but some have not been completely elucidated. Here, [...] Read more.
Crystalline (Cry) proteins from Bacillus thuringiensis (Bt) are widely used in sprays and transgenic crops to control insect pests, but the evolution of insect resistance threatens their long-term use. Different resistance mechanisms have been identified, but some have not been completely elucidated. Here, the transcriptome of the midgut and proteome of the peritrophic matrix (PM) were comparatively analyzed to identify potential mechanism of resistance to Cry1Ac in laboratory-selected strain XJ10 of Helicoverpa armigera. This strain had a 146-fold resistance to Cry1Ac protoxin and 45-fold resistance to Cry1Ac activated toxin compared with XJ strain. The mRNA and protein levels for several trypsin genes were downregulated in XJ10 compared to the susceptible strain XJ. Furthermore, 215 proteins of the PM were identified, and nearly all had corresponding mRNAs in the midgut. These results provide new insights that the PM may participate in Bt resistance. Full article
(This article belongs to the Special Issue Insecticidal Toxins from Bacillus thuringiensis)
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12 pages, 2048 KiB  
Article
The C-Terminal Domain of the Bacillus thuringiensis Cry4Ba Mosquito-Specific Toxin Serves as a Potential Membrane Anchor
by Anon Thammasittirong, Chompounoot Imtong, Wilaiwan Sriwimol, Somsri Sakdee and Chanan Angsuthanasombat
Toxins 2019, 11(2), 62; https://doi.org/10.3390/toxins11020062 - 23 Jan 2019
Cited by 6 | Viewed by 2535
Abstract
Although the C-terminal domain (DIII) of three-domain Cry insecticidal toxins from Bacillus thuringiensis has been implicated in various biological functions, its exact role still remains to be elucidated. Here, the 21-kDa isolated DIII fragment of the 65-kDa Cry4Ba mosquito-specific toxin was analyzed for [...] Read more.
Although the C-terminal domain (DIII) of three-domain Cry insecticidal toxins from Bacillus thuringiensis has been implicated in various biological functions, its exact role still remains to be elucidated. Here, the 21-kDa isolated DIII fragment of the 65-kDa Cry4Ba mosquito-specific toxin was analyzed for its binding characteristics toward lipid-bilayer membranes. When the highly-purified Cry4Ba-DIII protein was structurally verified by attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy, it revealed the presence of a distinct β-sheet structure, corresponding to its structure embodied in the Cry4Ba crystal structure. Binding analysis via surface plasmon resonance (SPR) spectroscopy revealed that the 21-kDa Cry4Ba-DIII truncate displayed tight binding to immobilized liposome membranes in a two-step manner, exhibiting a dissociation rate constant (kd) comparable to the 65-kDa full-length toxin. Also similar to the Cry4Ba full-length toxin, its isolated DIII truncate was able to anchor a part of its molecule into the immobilized membrane as the SPR signal was still detected after prolonged treatment with proteinase K. However, unlike the full-length active toxin, the DIII truncate was unable to induce membrane permeability of calcein-loaded liposomes or ion-channel formation in planar lipid bilayers. Together, our present data have disclosed a pivotal role of C-terminal DIII in serving as a membrane anchor rather than a pore-forming moiety of the Cry4Ba mosquito-active toxin, highlighting its potential mechanistic contribution to the interaction of the full-length toxin with lipid membranes in mediating toxicity. Full article
(This article belongs to the Special Issue Insecticidal Toxins from Bacillus thuringiensis)
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13 pages, 966 KiB  
Article
Bacillus thuringiensis Maize Expressing a Fusion Gene Cry1Ab/Cry1AcZM Does Not Harm Valued Pollen Feeders
by Xiaowei Xie, Zhifu Cui, Yanan Wang, Yuanyuan Wang, Fengqin Cao, Jörg Romeis, Yufa Peng and Yunhe Li
Toxins 2019, 11(1), 8; https://doi.org/10.3390/toxins11010008 - 26 Dec 2018
Cited by 4 | Viewed by 4457
Abstract
The ladybird Propylea japonica, adults of the green lacewing Chrysoperla nipponensis and the honey bee Apis mellifera are common pollen feeders in many crop systems. They could therefore be directly exposed to Cry proteins in Bacillus thuringiensis (Bt)-transgenic crop fields [...] Read more.
The ladybird Propylea japonica, adults of the green lacewing Chrysoperla nipponensis and the honey bee Apis mellifera are common pollen feeders in many crop systems. They could therefore be directly exposed to Cry proteins in Bacillus thuringiensis (Bt)-transgenic crop fields by ingestion of pollen. They, or closely related species, are therefore often selected as surrogate test species in non-target risk assessment of Bt plants. In the current study, we evaluated the potential effects of the ingestion of Bt maize pollen containing the Cry1Ab/Cry1Ac fusion protein on various life-table parameters of the three pollen-feeding non-target species in laboratory feeding assays. The results showed that pupation rate and male adult fresh weight of P. japonica were significantly increased when fed pollen from Bt maize compared to control maize pollen, but other test life-table parameters were not affected. For the other two species, none of the tested life-table parameters (survival, pre-oviposition period, fecundity and adult fresh weight for C. nipponensis; survival and mean acinus diameter of hypopharyngeal glands for A. mellifera) differed between non-Bt and Bt maize pollen treatments. ELISA measurements confirmed the stability and uptake of the Cry protein by all three species during the feeding bioassays. In addition, a sensitive insect bioassay confirmed the bioactivity of the Cry1Ab/Cry1Ac protein in the Bt maize pollen used. Overall, the results suggested that the three pollen feeders are not sensitive to the Cry1Ab/Cry1Ac protein, and planting of the Bt maize variety will pose a negligible risk to P. japonica, adult C. nipponensis and adult A. mellifera. Full article
(This article belongs to the Special Issue Insecticidal Toxins from Bacillus thuringiensis)
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10 pages, 3139 KiB  
Article
Fibroblast Growth Factor Receptor, a Novel Receptor for Vegetative Insecticidal Protein Vip3Aa
by Kun Jiang, Xiaoyue Hou, Lu Han, Tongtong Tan, Zhanglei Cao and Jun Cai
Toxins 2018, 10(12), 546; https://doi.org/10.3390/toxins10120546 - 18 Dec 2018
Cited by 30 | Viewed by 3860
Abstract
Vegetative insecticidal proteins (Vips), which are secreted by some Bacillus thuringiensis strains during vegetative growth, exhibit high virulence to many pests. Vip3A proteins have been used commercially both in some bio-insecticides and in transgenic crops; however, compared with insecticidal crystal proteins, the mechanism [...] Read more.
Vegetative insecticidal proteins (Vips), which are secreted by some Bacillus thuringiensis strains during vegetative growth, exhibit high virulence to many pests. Vip3A proteins have been used commercially both in some bio-insecticides and in transgenic crops; however, compared with insecticidal crystal proteins, the mechanism of action of Vip3A is still unclear. In this work, we indicated that the fibroblast growth factor receptor-like protein (Sf-FGFR) from the membrane of Sf9 cells could bind to Vip3Aa. The interaction between Vip3Aa and Sf-FGFR was confirmed by pull-down assays and dot blotting experiment in vitro. The binding affinity between Vip3Aa and extracellular regions of Sf-FGFR (GST-FGFR-N) was determined by microscale thermophoresis assay (MST). Moreover, Vip3Aa-Flag could be co-immunoprecipitated with Sf-FGFR-V5 ex vivo. Furthermore, knockdown of Sf-FGFR gene in Sf9 cells resulted in reducing the mortality of those cells to Vip3Aa. In summary, our data indicated that Sf-FGFR is a novel receptor for Vip3Aa. Full article
(This article belongs to the Special Issue Insecticidal Toxins from Bacillus thuringiensis)
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17 pages, 1971 KiB  
Article
Impact of Antibiotics on Efficacy of Cry Toxins Produced in Two Different Genetically Modified Bt Maize Varieties in Two Lepidopteran Herbivore Species, Ostrinia nubilalis and Spodoptera littoralis
by Angelika Hilbeck, Nicolas Defarge, Thomas Bøhn, Michelle Krautter, Constanze Conradin, Caroline Amiel, Jean-Michel Panoff and Miluse Trtikova
Toxins 2018, 10(12), 489; https://doi.org/10.3390/toxins10120489 - 23 Nov 2018
Cited by 14 | Viewed by 6006
Abstract
The insecticidal crystal proteins from Bacillus thuringiensis (Bt) are widely-used biopesticides that are used both as Bt spore-crystal preparations in sprayable formulations and as activated toxins in genetically modified (GM) plants. Models for their modes of action have been proposed but many issues [...] Read more.
The insecticidal crystal proteins from Bacillus thuringiensis (Bt) are widely-used biopesticides that are used both as Bt spore-crystal preparations in sprayable formulations and as activated toxins in genetically modified (GM) plants. Models for their modes of action have been proposed but many issues remain unresolved. Among those is the role of commensal gut bacteria in target insect death: previous studies showed that antibiotics attenuate the toxicity of Bt sprays. We tested whether antibiotics interfere with the effects of GM plant-produced Bt toxins in larvae of two Lepidopteran species, the European corn borer Ostrinia nubilalis and the cotton leafworm Spodoptera littoralis. The larvae were reared on artificial diet with or without antibiotics and, thereafter, fed two varieties of Bt GM maize in comparison to conventional non-Bt maize leaves sprayed with antibiotic solution and/or with a Bt formulation. Antibiotics significantly reduced or delayed the toxicity of Cry toxins, although to a lesser extent than previously reported for Bt-sprays. This supports the hypothesis that Cry toxins induce mortality by themselves in the absence of Bt bacteria and spores, and of commensal gut bacteria. However, larvae that were not treated with antibiotics died faster and at a higher rate which was further compounded by plant variety and species sensitivity. These findings support a hypothesis that toxicemia alone can inflict significant mortality. However, in the absence of antibiotics, the gut bacteria likely enhance the Cry toxin effect by inflicting, additionally, bacterial septicemia. This has important implications in field situations where antibiotic substances are present—e.g., from manure of animals from conventional production systems—and for ecotoxicological testing schemes of Bt toxins and nontarget organisms that are often using artificial diets enriched with high concentrations of antibiotics. Full article
(This article belongs to the Special Issue Insecticidal Toxins from Bacillus thuringiensis)
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10 pages, 296 KiB  
Article
Insecticidal Activity and Synergistic Combinations of Ten Different Bt Toxins against Mythimna separata (Walker)
by Jing Yang, Yudong Quan, Prabu Sivaprasath, Muhammad Zeeshan Shabbir, Zhenying Wang, Juan Ferré and Kanglai He
Toxins 2018, 10(11), 454; https://doi.org/10.3390/toxins10110454 - 04 Nov 2018
Cited by 28 | Viewed by 4419
Abstract
The oriental armyworm (OAW), Mythimna separata (Walker), is a destructive pest of agricultural crops in Asia and Australia. Commercialized Bt crops have performed very well against their target pests; however, very few studies have been done on the susceptibility of OAW to Bt [...] Read more.
The oriental armyworm (OAW), Mythimna separata (Walker), is a destructive pest of agricultural crops in Asia and Australia. Commercialized Bt crops have performed very well against their target pests; however, very few studies have been done on the susceptibility of OAW to Bt toxins in either sprays or expressed in Bt crops. In this work, we evaluated the toxicities of Cry1Ab, Cry1Ac, Cry1Ah, Cry1Fa, Cry2Aa, Cry2Ab, Cry1Ie, Vip3Aa19, Vip3Aa16, and Vip3Ca against OAW neonate larvae, as well as the interaction between Cry and Vip toxins. The results from bioassays revealed that LC50 (lethal concentration for 50% mortality) values ranged from 1.6 to 78.6 μg/g (toxin/diet) for those toxins. Among them, Vip3 proteins, along with Cry1A proteins and Cry2Aa, were the ones with the highest potency, with LC50 values ranging from 1.6 to 7.4 μg/g. Synergism between Cry and Vip toxins was observed, being high in the combination of Vip3Aa16 with Cry1 toxins, with synergetic factors ranging from 2.2 to 9.2. The Vip3Ca toxin did not show any synergistic effect with any of the toxins tested. These results can help in designing new combinations of pyramiding genes in Bt crops, as well as in recombinant bacteria, for the control of OAW as well as for resistance management programs. Full article
(This article belongs to the Special Issue Insecticidal Toxins from Bacillus thuringiensis)
11 pages, 2065 KiB  
Article
C-Type Lectin-20 Interacts with ALP1 Receptor to Reduce Cry Toxicity in Aedes aegypti
by Khadija Batool, Intikhab Alam, Guohui Zhao, Junxiang Wang, Jin Xu, Xiaoqiang Yu, Enjiong Huang, Xiong Guan and Lingling Zhang
Toxins 2018, 10(10), 390; https://doi.org/10.3390/toxins10100390 - 25 Sep 2018
Cited by 17 | Viewed by 3286
Abstract
Aedes aegypti is a crucial vector for human diseases, such as yellow fever, dengue, chikungunya, and Zika viruses. Today, a major challenge throughout the globe is the insufficient availability of antiviral drugs and vaccines against arboviruses, and toxins produced by Bacillus thuringiensis (Bt) [...] Read more.
Aedes aegypti is a crucial vector for human diseases, such as yellow fever, dengue, chikungunya, and Zika viruses. Today, a major challenge throughout the globe is the insufficient availability of antiviral drugs and vaccines against arboviruses, and toxins produced by Bacillus thuringiensis (Bt) are still used as biological agents for mosquito control. The use of Cry toxins to kill insects mainly depends on the interaction between Cry toxins and important toxin receptors, such as alkaline phosphatase (ALP). In this study, we investigated the function of A. aegypti C-type lectin-20 (CTL-20) in the tolerance of Cry toxins. We showed that recombinant CTL-20 protein interacted with both Cry11Aa and ALP1 by the Far-Western blot and ELISA methods, and CTL-20 bound to A. aegypti larval brush border membrane vesicles (BBMVs). Binding affinity of CTL-20 to ALP1 was higher than that of Cry11Aa to ALP1. Furthermore, the survival rate of A. aegypti larvae fed with Cry11Aa toxin mixed with recombinant CTL-20 fusion protein was significantly increased compared with that of the control larvae fed with Cry11Aa mixed with thioredoxin. Our novel results suggest that midgut proteins like CTLs may interfere with interactions between Cry toxins and toxin receptors by binding to both Cry toxins and receptors to alter Cry toxicity. Full article
(This article belongs to the Special Issue Insecticidal Toxins from Bacillus thuringiensis)
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18 pages, 1428 KiB  
Article
A Genomic and Proteomic Approach to Identify and Quantify the Expressed Bacillus thuringiensis Proteins in the Supernatant and Parasporal Crystal
by Joaquín Gomis-Cebolla, Ana Paula Scaramal Ricietto and Juan Ferré
Toxins 2018, 10(5), 193; https://doi.org/10.3390/toxins10050193 - 10 May 2018
Cited by 8 | Viewed by 4358
Abstract
The combined analysis of genomic and proteomic data allowed us to determine which cry and vip genes are present in a Bacillus thuringiensis (Bt) isolate and which ones are being expressed. Nine Bt isolates were selected from Spanish collections of Bt [...] Read more.
The combined analysis of genomic and proteomic data allowed us to determine which cry and vip genes are present in a Bacillus thuringiensis (Bt) isolate and which ones are being expressed. Nine Bt isolates were selected from Spanish collections of Bt based on their vip1 and vip2 gene content. As a first step, nine isolates were analyzed by PCR to select those Bt isolates that contained genes with the lowest similarity to already described vip1 and vip2 genes (isolates E-SE10.2 and O-V84.2). Two selected isolates were subjected to a combined genomic and proteomic analysis. The results showed that the Bt isolate E-SE10.2 codifies for two new vegetative proteins, Vip2Ac-like_1 and Sip1Aa-like_1, that do not show expression differences at 24 h vs. 48 h and are expressed in a low amount. The Bt isolate O-V84.2 codifies for three new vegetative proteins, Vip4Aa-like_1, Vip4Aa-like_2, and Vip2Ac-like_2, that are marginally expressed. The Vip4Aa-like_1 protein was two-fold more abundant at 24 h vs. 48 h, while the Vip4Aa-like_2 was detected only at 24 h. For Vip2Ac-like_2, no differences in expression were found at 24 h vs. 48 h. Moreover, the parasporal crystal of the E-SE10.2 isolate contains a single type of crystal protein, Cry23Aa-like, while the parasporal crystal from O-V84.2 contains three kinds of crystal proteins: 7.0–9.8% weight of Cry45Aa-like proteins, 35–37% weight of Cry32-like proteins and 2.8–4.3% weight of Cry73-like protein. Full article
(This article belongs to the Special Issue Insecticidal Toxins from Bacillus thuringiensis)
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Review

Jump to: Research

17 pages, 2093 KiB  
Review
Function and Role of ATP-Binding Cassette Transporters as Receptors for 3D-Cry Toxins
by Ryoichi Sato, Satomi Adegawa, Xiaoyi Li, Shiho Tanaka and Haruka Endo
Toxins 2019, 11(2), 124; https://doi.org/10.3390/toxins11020124 - 19 Feb 2019
Cited by 48 | Viewed by 5774
Abstract
When ABC transporter family C2 (ABCC2) and ABC transporter family B1 (ABCB1) were heterologously expressed in non-susceptible cultured cells, the cells swelled in response to Cry1A and Cry3 toxins, respectively. Consistent with the notion that 3D-Cry toxins form cation-permeable pores, Bombyx mori ABCC2 [...] Read more.
When ABC transporter family C2 (ABCC2) and ABC transporter family B1 (ABCB1) were heterologously expressed in non-susceptible cultured cells, the cells swelled in response to Cry1A and Cry3 toxins, respectively. Consistent with the notion that 3D-Cry toxins form cation-permeable pores, Bombyx mori ABCC2 (BmABCC2) facilitated cation-permeable pore formation by Cry1A when expressed in Xenopus oocytes. Furthermore, BmABCC2 had a high binding affinity (KD) to Cry1Aa of 3.1 × 10−10 M. These findings suggest that ABC transporters, including ABCC2 and ABCB1, are functional receptors for 3D-Cry toxins. In addition, the Cry2 toxins most distant from Cry1A toxins on the phylogenetic tree used ABC transporter A2 as a receptor. These data suggest that 3D-Cry toxins use ABC transporters as receptors. In terms of inducing cell swelling, ABCC2 has greater activity than cadherin-like receptor. The pore opening of ABC transporters was hypothesized to be linked to their receptor function, but this was repudiated by experiments using mutants deficient in export activity. The synergistic relationship between ABCC2 and cadherin-like receptor explains their ability to cause resistance in one species of insect. Full article
(This article belongs to the Special Issue Insecticidal Toxins from Bacillus thuringiensis)
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