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Toxins
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Insecticidal Toxins from Bacillus thuringiensis 2021–2022
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Insecticidal Toxins from Bacillus thuringiensis 2021–2022

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

Deadline for manuscript submissions: closed (31 October 2022) | Viewed by 10501

Special Issue Editors

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
Prof. Dr. Mario Soberon

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 Issue Information

Dear Colleagues,

Bacillus thuringiensis (Bt) and Lysinibacillus sphaericus are soil born bacteria that produce a variety of toxins with specificity against different insect species or nematodes. One of the most important characteristics of the toxins produced by these bacteria is their high specificity against their target organisms, showing no toxicity against other insects or to humans. Different Bt and L sphaericus strains have been used to make products highly effective in the control insect pests or insects that are vectors of human diseases. Additionally, the genes of certain Bt toxins have been expressed in plants for the efficient control of crop pests.

This Special Issue will focus on progress in the characterization of novel insecticidal Bt and L. sphaericus toxins, including Cry, Cyt, Vip, Vpa, Vpb, App, Xbp, Mpp, Mtx, Spp, Tpp, and Gpp. Studies concerning their expression regulation, mode of action, structure, and  synergism among these proteins as well as analysis of the resistance mechanisms and intracelular responses in the different targets are welcome. This knowledge is likely to provide a sustainable  method of use for this technology for insect pest and nematode control. Your scientific input into this Special Issue will be much appreciated.

Prof. Dr. Alejandra Bravo
Prof. Dr. Mario Soberon
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a double-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Toxins is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2700 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Bacillus thuringiensis
  • Lysinibacillus sphaericus Bt toxins
  • expression regulation
  • mode of action
  • structure
  • synergism
  • resistance mechanisms
  • intracellular responses

Related Special Issue

Published Papers (5 papers)

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Research

14 pages, 3297 KiB  
Article
Aromatic Residues on the Side Surface of Cry4Ba-Domain II of Bacillus thuringiensis subsp. israelensis Function in Binding to Their Counterpart Residues on the Aedes aegypti Alkaline Phosphatase Receptor
by Anon Thammasittirong and Sutticha Na-Ranong Thammasittirong
Toxins 2023, 15(2), 114; https://doi.org/10.3390/toxins15020114 - 29 Jan 2023
Cited by 1 | Viewed by 1204
Abstract
Receptor binding is a prerequisite process to exert the mosquitocidal activity of the Cry4Ba toxin of Bacillus thuringiensis subsp. israelensis. The beta-sheet prism (domain II) and beta-sheet sandwich (domain III) of the Cry4Ba toxin have been implicated in receptor binding, albeit the [...] Read more.
Receptor binding is a prerequisite process to exert the mosquitocidal activity of the Cry4Ba toxin of Bacillus thuringiensis subsp. israelensis. The beta-sheet prism (domain II) and beta-sheet sandwich (domain III) of the Cry4Ba toxin have been implicated in receptor binding, albeit the precise binding mechanisms of these remain unclear. In this work, alanine scanning was used to determine the contribution to receptor binding of some aromatic and hydrophobic residues on the surface of domains II and III that are predicted to be responsible for binding to the Aedes aegypti membrane-bound alkaline phosphatase (Aa-mALP) receptor. Larvicidal activity assays against A. aegypti larvae revealed that aromatic residues (Trp327 on the β2 strand, Tyr347 on the β3–β4 loop, and Tyr359 on the β4 strand) of domain II were important to the toxicity of the Cry4Ba toxin. Quantitative binding assays using enzyme-linked immunosorbent assay (ELISA) showed similar decreasing trends in binding to the Aa-mALP receptor and in toxicity of the Cry4Ba mutants Trp327Ala, Tyr347Ala, and Tyr359Ala, suggesting that a possible function of these surface-exposed aromatic residues is receptor binding. In addition, binding assays of the Cry4Ba toxin to the mutants of the binding residues Gly513, Ser490, and Phe497 of the Aa-mALP receptor supported the binding function of Trp327, Tyr347, and Tyr359 of the Cry4Ba toxin, respectively. Altogether, our results showed for the first time that aromatic residues on a side surface of the Cry4Ba domain II function in receptor binding. This finding provides greater insight into the possible molecular mechanisms of the Cry4Ba toxin. Full article
(This article belongs to the Special Issue Insecticidal Toxins from Bacillus thuringiensis 2021–2022)
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14 pages, 3192 KiB  
Article
eCry1Gb.1Ig, A Novel Chimeric Cry Protein with High Efficacy against Multiple Fall Armyworm (Spodoptera frugiperda) Strains Resistant to Different GM Traits
by Hyunsook Chae, Zhimou Wen, Travis Hootman, Jo Himes, Qianqian Duan, Joel McMath, Jesse Ditillo, Richard Sessler, Jared Conville, Ying Niu, Phillip Matthews, Fabricio Francischini, Fangneng Huang and Matthew Bramlett
Toxins 2022, 14(12), 852; https://doi.org/10.3390/toxins14120852 - 03 Dec 2022
Cited by 4 | Viewed by 2729
Abstract
Spodoptera frugiperda (fall armyworm, FAW) is one of the most devastating insect pests to corn and soybean production in the Americas and is rapidly expanding its range worldwide. It is known to be hard to control either by chemical insecticide applications or by [...] Read more.
Spodoptera frugiperda (fall armyworm, FAW) is one of the most devastating insect pests to corn and soybean production in the Americas and is rapidly expanding its range worldwide. It is known to be hard to control either by chemical insecticide applications or by GM. Although the use of GM traits can be an effective way to control this pest, it is very rare to find native insecticidal proteins that provide the necessary level of FAW control in crop fields where FAW pressure and damage are high. Insecticidal Cry proteins sourced from Bacillus thuringiensis have been heavily utilized in the development of crops with GM traits; however, it is increasingly difficult to identify Cry proteins with unique modes of action. Protein engineering via a phylogenetically guided Cry protein domain swapping approach enabled us to discover novel chimeric Cry proteins engineered from inactive parent sequences. Some of these chimeras show excellent efficacy against key biotypes of FAW from Brazil and North America. In this study, we characterized a Cry-based chimera eCry1Gb.1Ig that is a very potent FAW toxin. eCry1Gb.1Ig showed high efficacy against multiple FAW strains that are resistant to various traits, including Cry1Fa, Vip3Aa and Cry1A.105/Cry2Ab. These results clearly indicate that the FAW strains resistant to Cry1Fa, Vip3Aa or Cry1A.105/Cry2Ab demonstrate no cross-resistance to eCry1Gb.1Ig and strongly suggest that eCry1Gb.1Ig acts through a novel mode of action compared to the existing traits. In addition to its FAW activity, eCry1Gb.1Ig has also been shown to control Chrysodeixis includens (soybean looper, SBL) and Anticarsia gemmatalis (velvetbean caterpillar, VBC), which are significant pests of soybean. When eCry1Gb.1Ig was introduced into corn and soybean crops, transgenic events showed strong efficacy against FAW, SBL and VBC, but no adverse plant phenotypes. This suggests that the in planta expression of the eCry1Gb.1Ig protein does not compromise plant growth or reproduction and can protect plants from FAW-related damage. Therefore, this valuable discovery will provide a differentiating FAW control trait that will give growers another tool to help them reduce yield loss due to FAW. Full article
(This article belongs to the Special Issue Insecticidal Toxins from Bacillus thuringiensis 2021–2022)
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19 pages, 3363 KiB  
Article
Cry4Aa and Cry4Ba Mosquito-Active Toxins Utilize Different Domains in Binding to a Particular Culex ALP Isoform: A Functional Toxin Receptor Implicating Differential Actions on Target Larvae
by Manussawee Dechkla, Sathapat Charoenjotivadhanakul, Chompounoot Imtong, Sarinporn Visitsattapongse, Hui-Chun Li and Chanan Angsuthanasombat
Toxins 2022, 14(10), 652; https://doi.org/10.3390/toxins14100652 - 21 Sep 2022
Cited by 3 | Viewed by 1586
Abstract
The three-domain Cry4Aa toxin produced from Bacillus thuringiensis subsp. israelensis was previously shown to be much more toxic to Culex mosquito larvae than its closely related toxin—Cry4Ba. The interaction of these two individual toxins with target receptors on susceptible larval midgut cells is [...] Read more.
The three-domain Cry4Aa toxin produced from Bacillus thuringiensis subsp. israelensis was previously shown to be much more toxic to Culex mosquito larvae than its closely related toxin—Cry4Ba. The interaction of these two individual toxins with target receptors on susceptible larval midgut cells is likely to be the critical determinant in their differential toxicity. Here, two full-length membrane-bound alkaline phosphatase (mALP) isoforms from Culex quinquefasciatus larvae, Cq-mALP1263and Cq-mALP1264, predicted to be GPI-linked was cloned and functionally expressed in Spodoptera frugiperda (Sf9) cells as 57- and 61-kDa membrane-bound proteins, respectively. Bioinformatics analysis disclosed that both Cq-mALP isoforms share significant sequence similarity to Aedes aegypti-mALP—a Cry4Ba toxin receptor. In cytotoxicity assays, Sf9 cells expressing Cq-mALP1264, but not Cq-mALP1263, showed remarkably greater susceptibility to Cry4Aa than Cry4Ba, while immunolocalization studies revealed that both toxins were capable of binding to each Cq-mALP expressed on the cell membrane surface. Molecular docking of the Cq-mALP1264-modeled structure with individual Cry4 toxins revealed that Cry4Aa could bind to Cq-mALP1264 primarily through particular residues on three surface-exposed loops in the receptor-binding domain—DII, including Thr512, Tyr513 and Lys514 in the β10-β11loop. Dissimilarly, Cry4Ba appeared to utilize only certain residues in its C-terminal domain—DIII to interact with such a Culex counterpart receptor. Ala-substitutions of selected β10-β11loop residues (T512A, Y513A and K514A) revealed that only the K514A mutant displayed a drastic decrease in biotoxicity against C. quinquefasciatus larvae. Further substitution of Lys514 with Asp (K514D) revealed a further decrease in larval toxicity. Furthermore, in silico calculation of the binding affinity change (ΔΔGbind) in Cry4Aa-Cq-mALP1264 interactions upon these single-substitutions revealed that the K514D mutation displayed the largest ΔΔGbind value as compared to three other mutations, signifying an adverse impact of a negative charge at this critical receptor-binding position. Altogether, our present study has disclosed that these two related-Cry4 mosquito-active toxins conceivably exploited different domains in functional binding to the same Culex membrane-bound ALP isoform—Cq-mALP1264 for mediating differential toxicity against Culex target larvae. Full article
(This article belongs to the Special Issue Insecticidal Toxins from Bacillus thuringiensis 2021–2022)
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15 pages, 1026 KiB  
Article
Could the Presence of Thrips AFFECT the Yield Potential of Genetically Modified and Conventional Maize?
by Ľudovít Cagáň, Peter Bokor and Oxana Skoková Habuštová
Toxins 2022, 14(7), 502; https://doi.org/10.3390/toxins14070502 - 19 Jul 2022
Viewed by 1723
Abstract
Maize pests like Ostrinia nubilalis and Diabrotica virgifera virgifera are eradicated using genetically modified maize. This study’s goal was to see if the genetically modified maize MON810 is also toxic to thrips communities on maize. The impact of Bt maize on thrips diversity [...] Read more.
Maize pests like Ostrinia nubilalis and Diabrotica virgifera virgifera are eradicated using genetically modified maize. This study’s goal was to see if the genetically modified maize MON810 is also toxic to thrips communities on maize. The impact of Bt maize on thrips diversity and abundance, as well as yield losses, was studied in the field in Borovce for three years (Slovakia). The study used 10 Bt and 10 non-Bt maize cultivars. Thrips were monitored every two weeks during the season using transparent sticky traps installed on the experimental plots (one per plot, 20 per year). In total, 3426 thrips were caught. Thrips populations usually peak around the end of July at BBCH55. Among the species identified were Limothrips denticornis, Limothrips cerealium, Haplothrips aculeatus, Frankliniella schultzei, Frankliniella occidentalis, Thrips tabaci, Aeolothrips fasciatus, Frankliniella tenuicornis, and Chirothrips spp. We found that MON810 maize had no effect on the occurrence or composition of thrips. Their presence was affected by the maize growth phase and growing seasons and partially by the weather. The direct effect on the grain yield was not confirmed. Our research contributed to scientific knowledge of thrips communities found on maize plants in Central Europe, including Bt maize. Full article
(This article belongs to the Special Issue Insecticidal Toxins from Bacillus thuringiensis 2021–2022)
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Graphical abstract

15 pages, 357 KiB  
Article
Resistance Allele Frequency to Cry1Ab and Vip3Aa20 in Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae) in Louisiana and Three Other Southeastern U.S. States
by Shucong Lin, Isaac Oyediran, Ying Niu, Sebe Brown, Don Cook, Xinzhi Ni, Yan Zhang, Francis P. F. Reay-Jones, Jeng Shong Chen, Zhimou Wen, Marcelo Dimase and Fangneng Huang
Toxins 2022, 14(4), 270; https://doi.org/10.3390/toxins14040270 - 11 Apr 2022
Cited by 10 | Viewed by 2083
Abstract
The corn earworm/bollworm, Helicoverpa zea (Boddie), is a pest species that is targeted by both Bacillus thuringiensis (Bt) maize and cotton in the United States. Cry1Ab and Vip3Aa20 are two common Bt toxins that are expressed in transgenic maize. The objective of this [...] Read more.
The corn earworm/bollworm, Helicoverpa zea (Boddie), is a pest species that is targeted by both Bacillus thuringiensis (Bt) maize and cotton in the United States. Cry1Ab and Vip3Aa20 are two common Bt toxins that are expressed in transgenic maize. The objective of this study was to determine the resistance allele frequency (RAF) to Cry1Ab and Vip3Aa20 in H. zea populations that were collected during 2018 and 2019 from four southeastern U.S. states: Louisiana, Mississippi, Georgia, and South Carolina. By using a group-mating approach, 104 F2 iso-lines of H. zea were established from field collections with most iso-lines (85) from Louisiana. These F2 iso-lines were screened for resistance alleles to Cry1Ab and Vip3Aa20, respectively. There was no correlation in larval survivorship between Cry1Ab and Vip3Aa20 when the iso-lines were exposed to these two toxins. RAF to Cry1Ab maize was high (0.256) and the RAFs were similar between Louisiana and the other three states and between the two sampling years. In contrast, no functional major resistance allele (RA) that allowed resistant insects to survive on Vip3Aa20 maize was detected and the expected RAF of major RAs with 95% probability was estimated to 0 to 0.0073. However, functional minor RAs to Vip3Aa20 maize were not uncommon; the estimated RAF for minor alleles was 0.028. The results provide further evidence that field resistance to Cry1Ab maize in H. zea has widely occurred, while major RAs to Vip3Aa20 maize are uncommon in the southeastern U.S. region. Information that was generated from this study should be useful in resistance monitoring and refinement of resistance management strategies to preserve Vip3A susceptibility in H. zea. Full article
(This article belongs to the Special Issue Insecticidal Toxins from Bacillus thuringiensis 2021–2022)
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