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Toxins
Special Issues
Mode of Action of Proteinaceous Toxins Produced by Bacillus thuringiensis
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Mode of Action of Proteinaceous Toxins Produced by Bacillus thuringiensis

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

Deadline for manuscript submissions: closed (30 April 2022) | Viewed by 14944

Special Issue Editor

Dr. Haruka Endo

E-Mail
Guest Editor
Department of Integrated Bioscience, Graduate School of Frontier Sciences, The University of Tokyo, Kashiwa, Chiba, Japan
Interests: what is happening on the cell membrane from toxin-receptor interactions to pore formation; what the essence is of being a toxin receptor mediating high toxicity; co-evolution between cry toxins and host ABC transporters

Special Issue Information

Dear Colleagues,

Bacillus thuringiensis (Bt) produces a diversity of proteinaceous toxins, some of which are widely used for pest control in agriculture. The discovery of ABC transporters serving as receptors for Cry1A, Cry2A, and Cry3 toxins in the 2010s served as a breakthrough in research into mode of action of Cry toxin. In particular, key receptors for Cry1A toxins seem to be almost here. However, we are still far from an essential understanding of how Cry toxins form pores in the insect cell membrane via interactions with receptors. With regard to the remaining ~70 classes of Cry toxins, Vip toxins, and other Bt toxins, their receptors have not been identified or more research is needed to determine the role of receptor candidates.

The aim of this Special Issue is to provide seeds that will generate the next breakthrough in Bt research toward a complete understanding of the mode of action of Bt toxins. For that purpose, groundbreaking findings supported by a limited set of experiments are welcome. Negative results confirming or conflicting with previous reports are also welcome. Topics are not limited to receptor interaction but include the whole aspect of the mode of action (see Keywords). I look forward to your contribution.

Dr. Haruka Endo
Guest Editor

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

  • Proteinaceous toxins from Bt
  • Toxin–receptor interaction
  • Mechanism of cell death
  • Mechanism of resistance
  • Insecticidal spectrum and specificity
  • Evolution and diversity of toxins
  • Factors affecting Bt susceptibility
  • Host responses to toxin attack
  • Strategy and engineering for application

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Published Papers (4 papers)

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19 pages, 3318 KiB  
Article
Temporal Exposure to Bt Insecticide Causes Oxidative Stress in Larval Midgut Tissue
by Biko K. Muita and Simon W. Baxter
Toxins 2023, 15(5), 323; https://doi.org/10.3390/toxins15050323 - 7 May 2023
Cited by 4 | Viewed by 3136
Abstract
Bacillus thuringiensis (Bt) three-domain Cry toxins are highly successful biological pesticides; however, the mechanism through which they cause death to targeted larval midgut cells is not fully understood. Herein, we challenged transgenic Bt-susceptible Drosophila melanogaster larvae with moderate doses of activated Cry1Ac toxin [...] Read more.
Bacillus thuringiensis (Bt) three-domain Cry toxins are highly successful biological pesticides; however, the mechanism through which they cause death to targeted larval midgut cells is not fully understood. Herein, we challenged transgenic Bt-susceptible Drosophila melanogaster larvae with moderate doses of activated Cry1Ac toxin and assessed the midgut tissues after one, three, and five hours using transmission electron microscopy and transcriptome sequencing. Larvae treated with Cry1Ac showed dramatic changes to their midgut morphology, including shortened microvilli, enlarged vacuoles, thickened peritrophic membranes, and swelling of the basal labyrinth, suggesting water influx. Transcriptome analysis showed that innate immune responses were repressed, genes involved with cell death pathways were largely unchanged, and mitochondria-related genes were strongly upregulated following toxin exposure. Defective mitochondria produced after toxin exposure were likely to contribute to significant levels of oxidative stress, which represent a common physiological response to a range of toxic chemicals. Significant reductions in both mitochondrial aconitase activity and ATP levels in the midgut tissue supported a rapid increase in reactive oxygen species (ROS) following exposure to Cry1Ac. Overall, these findings support the role of water influx, midgut cell swelling, and ROS activity in response to moderate concentrations of Cry1Ac. Full article
(This article belongs to the Special Issue Mode of Action of Proteinaceous Toxins Produced by Bacillus thuringiensis)
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17 pages, 2662 KiB  
Article
Transcriptional Analysis of Cotton Bollworm Strains with Different Genetic Mechanisms of Resistance and Their Response to Bacillus thuringiensis Cry1Ac Toxin
by Shan Yu, Chenyang Wang, Kaixia Li, Yihua Yang, Ya-Zhou He and Yidong Wu
Toxins 2022, 14(6), 366; https://doi.org/10.3390/toxins14060366 - 25 May 2022
Cited by 7 | Viewed by 2867
Abstract
Transgenic crops producing Bacillus thuringiensis (Bt) insecticidal proteins are grown widely for pest control, but the evolution of resistance in target pests could reduce their efficacy. Mutations in genes encoding cadherin, ABC transporter or tetraspanin were linked with resistance to Cry1Ac in several [...] Read more.
Transgenic crops producing Bacillus thuringiensis (Bt) insecticidal proteins are grown widely for pest control, but the evolution of resistance in target pests could reduce their efficacy. Mutations in genes encoding cadherin, ABC transporter or tetraspanin were linked with resistance to Cry1Ac in several lepidopteran insects, including the cotton bollworm (Helicoverpa armigera), a worldwide agricultural pest. However, the detailed molecular mechanisms by which these mutations confer insect resistance to Cry1Ac remain largely unknown. In this study, we analyzed the midgut transcriptomes of a susceptible SCD strain and three SCD-derived Cry1Ac-resistant strains of H. armigera (SCD-r1, with a naturally occurring deletion mutation of cadherin; SCD-KI, with a knock-in T92C point mutation in tetraspanin; and C2/3-KO, with both ABCC2 and ABCC3 knocked out). Evaluation of midgut transcript profiles of the four strains without Cry1Ac exposure identified many constitutively differentially expressed genes (DEGs) in the resistant SCD-r1 (n = 1355), SCD-KI (n = 1254) and C2/3-KO (n = 2055) strains. Analysis of DEGs in the midguts of each strain after Cry1Ac exposure revealed similar patterns of response to Cry1Ac in the SCD and SCD-r1 strains, but unique responses in the SCD-KI and C2/3-KO strains. Expression of midgut epithelium healing and defense-related genes was strongly induced by Cry1Ac intoxication in the SCD and SCD-r1 strains, while immune-related pattern recognition receptor and effector genes were highly expressed in the SCD-KI strain after Cry1Ac exposure. This study advances our knowledge of the transcriptomic basis for insect resistance to Bt toxins and provides a valuable resource for further molecular characterization of insect response to Cry1Ac toxin in H. armigera and other pest species. Full article
(This article belongs to the Special Issue Mode of Action of Proteinaceous Toxins Produced by Bacillus thuringiensis)
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16 pages, 4483 KiB  
Article
Probing the Mechanism of Action of Cry41Aa on HepG2 through the Establishment of a Resistant Subline
by Wided Souissi, Tweedie Alistair, Barbara Domanska, Eva Fortea, Michelle J. West, Jean-Louis Schwartz and Neil Crickmore
Toxins 2022, 14(5), 319; https://doi.org/10.3390/toxins14050319 - 29 Apr 2022
Cited by 1 | Viewed by 2472
Abstract
Cry41Aa, also called parasporin-3, belongs to a group of toxins from the entomopathogenic bacterium Bacillus thuringiensis that show activity against human cancer cells. Cry41Aa exhibits preferential cytocidal activity towards HL-60 (human promyelocytic leukaemia cells) and HepG2 (human liver cancer cells) cell lines after [...] Read more.
Cry41Aa, also called parasporin-3, belongs to a group of toxins from the entomopathogenic bacterium Bacillus thuringiensis that show activity against human cancer cells. Cry41Aa exhibits preferential cytocidal activity towards HL-60 (human promyelocytic leukaemia cells) and HepG2 (human liver cancer cells) cell lines after being proteolytically activated. To better understand the mechanism of action of Cry41Aa, we evolved resistance in HepG2 cells through repeated exposure to increasing doses of the toxin. Concentrations of Cry41Aa that killed over 50% of the parental HepG2 cells had no significant effect on the viability of the resistant cells and did not induce either pore formation or p38 phosphorylation (both characteristic features of pore-forming toxins). Preliminary RNA sequencing data identified AQP9 as a potential mediator of resistance, but extensive investigations failed to show a causal link and did not support an enhanced cell repair process as the resistance mechanism. Full article
(This article belongs to the Special Issue Mode of Action of Proteinaceous Toxins Produced by Bacillus thuringiensis)
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20 pages, 5225 KiB  
Perspective
Molecular and Kinetic Models for Pore Formation of Bacillus thuringiensis Cry Toxin
by Haruka Endo
Toxins 2022, 14(7), 433; https://doi.org/10.3390/toxins14070433 - 24 Jun 2022
Cited by 34 | Viewed by 5053
Abstract
Cry proteins from Bacillus thuringiensis (Bt) and other bacteria are pesticidal pore-forming toxins. Since 2010, when the ABC transporter C2 (ABCC2) was identified as a Cry1Ac protein resistant gene, our understanding of the mode of action of Cry protein has progressed substantially. ABCC2 [...] Read more.
Cry proteins from Bacillus thuringiensis (Bt) and other bacteria are pesticidal pore-forming toxins. Since 2010, when the ABC transporter C2 (ABCC2) was identified as a Cry1Ac protein resistant gene, our understanding of the mode of action of Cry protein has progressed substantially. ABCC2 mediates high Cry1A toxicity because of its high activity for helping pore formation. With the discovery of ABCC2, the classical killing model based on pore formation and osmotic lysis became nearly conclusive. Nevertheless, we are still far from a complete understanding of how Cry proteins form pores in the cell membrane through interactions with their host gut membrane proteins, known as receptors. Why does ABCC2 mediate pore formation with high efficiency unlike other Cry1A-binding proteins? Is the “prepore” formation indispensable for pore formation? What is the mechanism underlying the synergism between ABCC2 and the 12-cadherin domain protein? We examine potential mechanisms of pore formation via receptor interactions in this paper by merging findings from prior studies on the Cry mode of action before and after the discovery of ABC transporters as Cry protein receptors. We also attempt to explain Cry toxicity using Cry–receptor binding affinities, which successfully predicts actual Cry toxicity toward cultured cells coexpressing ABC transporters and cadherin. Full article
(This article belongs to the Special Issue Mode of Action of Proteinaceous Toxins Produced by Bacillus thuringiensis)
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