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Special Issue "Bacillus thuringiensis Toxins"

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

Deadline for manuscript submissions: closed (30 April 2014)

Special Issue Editor

Guest Editor
Prof. Dr. Anne-Brit Kolstø

Laboratory for Microbial Dynamics (LaMDa), Department of Pharmaceutical Biosciences, University of Oslo, Blindern, 0316, Oslo, Norway
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Special Issue Information

Dear Colleagues,

Bacillus thuringiensis is the most widely used biopesticide worldwide due to its production of proteinaceous crystal toxins. B. thuringiensis is part of the Bacillus cereus group, and the B. thuringiensis may be very closely related to B. cereus strains. The genes coding for these toxins are usually located on plasmids of varying sizes, ranging from a few kb to several hundred kb. The crystal toxins are most often produced during sporulation, and the toxins are regarded as specific for B. thuringiensis. Like the B. cereus strains, B. thuringiensis have the genes coding for several virulence factors, including enterotoxin genes, and these may well play a role in the pathogenic lifestyle that the B. thuringiensis display against insect larvae hosts. Still the specificity of each B. thuringiensis strain resides in the crystal toxin genes. More than 100 different crystal toxin genes have been identified, in addition to a great number of manipulated and improved toxin genes.

In this Special Issue of B. thuringiensis toxins, we seek new data on all aspects of the crystal toxins and other toxins produced by B. thuringiensis strains.  Both new data on gene regulation and toxin structure and mechanisms will be of interest, as will the importance of the toxins in the physiology of the bacteria and the hosts.

Prof. Dr. Anne-Brit Kolstø
Guest Editor

Submission

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are refereed through a 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 1400 CHF (Swiss Francs).


Keywords

  • host specificity of toxins
  • toxin gene regulation
  • modified toxins
  • non-Cry toxins
  • toxin stability
  • function of cry toxins and other toxins
  • resistance
  • toxin structure

Published Papers (20 papers)

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Research

Jump to: Review, Other

Open AccessArticle Evaluation of Cytotoxicity, Genotoxicity and Hematotoxicity of the Recombinant Spore-Crystal Complexes Cry1Ia, Cry10Aa and Cry1Ba6 from Bacillus thuringiensis in Swiss Mice
Toxins 2014, 6(10), 2872-2885; doi:10.3390/toxins6102872
Received: 29 April 2014 / Revised: 29 July 2014 / Accepted: 12 August 2014 / Published: 29 September 2014
Cited by 3 | PDF Full-text (483 KB) | HTML Full-text | XML Full-text
Abstract
The insecticidal properties of Cry-endotoxins from Bacillus thuringiensis (Bt) have long been used as spore-crystals in commercial spray formulations for insect control. Recently, some Bt-endotoxin genes have been cloned in many different plants. Toxicological evaluations of three spore-crystal endotoxins, BtCry1Ia, BtCry10Aa and BtCry1Ba6
[...] Read more.
The insecticidal properties of Cry-endotoxins from Bacillus thuringiensis (Bt) have long been used as spore-crystals in commercial spray formulations for insect control. Recently, some Bt-endotoxin genes have been cloned in many different plants. Toxicological evaluations of three spore-crystal endotoxins, BtCry1Ia, BtCry10Aa and BtCry1Ba6 from B. thuringiensis, were carried out on mice to understand their adverse effects on hematological systems and on genetic material. These three spore-crystals have shown toxic activity to the boll weevil, which is one of the most aggressive pests of the cotton crop. Cry1Ia, Cry10Aa and Cry1Ba6 did not increase the micronucleus frequency in the peripheral erythrocytes of mice and did not cause changes in the frequency of polychromatic erythrocytes. However, some hematologic disburbances were observed, specifically related to Cry1Ia and Cry1Ba6, respectively, for the erythroid and lymphoid lineage. Thus, although the profile of such adverse side effects can be related to their high level of exposure, which is not commonly found in the environment, results showed that these Bt spore-crystals were not harmless to mice, indicating that each spore-crystal endotoxin presents a characteristic profile of toxicity and might be investigated individually. Full article
(This article belongs to the Special Issue <i>Bacillus thuringiensis</i> Toxins)
Open AccessArticle Downregulation and Mutation of a Cadherin Gene Associated with Cry1Ac Resistance in the Asian Corn Borer, Ostrinia furnacalis (Guenée)
Toxins 2014, 6(9), 2676-2693; doi:10.3390/toxins6092676
Received: 30 April 2014 / Revised: 13 August 2014 / Accepted: 15 August 2014 / Published: 11 September 2014
Cited by 5 | PDF Full-text (732 KB) | HTML Full-text | XML Full-text
Abstract
Development of resistance in target pests is a major threat to long-term use of transgenic crops expressing Bacillus thuringiensis (Bt) Cry toxins. To manage and/or delay the evolution of resistance in target insects through the implementation of effective strategies, it is
[...] Read more.
Development of resistance in target pests is a major threat to long-term use of transgenic crops expressing Bacillus thuringiensis (Bt) Cry toxins. To manage and/or delay the evolution of resistance in target insects through the implementation of effective strategies, it is essential to understand the basis of resistance. One of the most important mechanisms of insect resistance to Bt crops is the alteration of the interactions between Cry toxins and their receptors in the midgut. A Cry1Ac-selected strain of Asian corn borer (ACB), Ostrinia furnacalis, a key pest of maize in China, evolved three mutant alleles of a cadherin-like protein (OfCAD) (MPR-r1, MPR-r2 and MPR-r3), which mapped within the toxin-binding region (TBR). Each of the three mutant alleles possessed two or three amino acid substitutions in this region, especially Thr1457→Ser. In highly resistant larvae (ACB-Ac200), MPR-r2 had a 26-amino acid residue deletion in the TBR, which resulted in reduced binding of Cry1Ac compared to the MPR from the susceptible strain, suggesting that the number of amino acid deletions influences the level of resistance. Furthermore, downregulation of OfCAD gene (ofcad) transcription was observed in the Cry1Ac resistant strain, ACB-Ac24, suggesting that Cry1Ac resistance in ACB is associated with the downregulation of the transcript levels of the cadherin-like protein gene. The OfCAD identified from ACB exhibited a high degree of similarity to other members of the cadherin super-family in lepidopteran species. Full article
(This article belongs to the Special Issue <i>Bacillus thuringiensis</i> Toxins)
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Open AccessArticle Inheritance Patterns, Dominance and Cross-Resistance of Cry1Ab- and Cry1Ac-Selected Ostrinia furnacalis (Guenée)
Toxins 2014, 6(9), 2694-2707; doi:10.3390/toxins6092694
Received: 30 April 2014 / Revised: 13 August 2014 / Accepted: 18 August 2014 / Published: 11 September 2014
Cited by 8 | PDF Full-text (572 KB) | HTML Full-text | XML Full-text
Abstract
Two colonies of Asian corn borer, Ostrinia furnacalis (Guenée), artificially selected from a Bt-susceptible colony (ACB-BtS) for resistance to Cry1Ab (ACB-AbR) and Cry1Ac (ACB-AcR) toxins, were used to analyze inheritance patterns of resistance to Cry1 toxins. ACB-AbR and ACB-AcR evolved significant levels of
[...] Read more.
Two colonies of Asian corn borer, Ostrinia furnacalis (Guenée), artificially selected from a Bt-susceptible colony (ACB-BtS) for resistance to Cry1Ab (ACB-AbR) and Cry1Ac (ACB-AcR) toxins, were used to analyze inheritance patterns of resistance to Cry1 toxins. ACB-AbR and ACB-AcR evolved significant levels of resistance, with resistance ratios (RR) of 39-fold and 78.8-fold to Cry1Ab and Cry1Ac, respectively. The susceptibility of ACB-AbR larvae to Cry1Ac and Cry1F toxins, which had not previously been exposed, were significantly reduced, being >113-fold and 48-fold, respectively. Similarly, susceptibility of ACB-AcR larvae to Cry1Ab and Cry1F were also significantly reduced (RR > nine-fold, RR > 18-fold, respectively), indicating cross-resistance among Cry1Ab, Cry1Ac, and Cry1F toxins. However, ACB-AbR and ACB-AcR larvae were equally susceptible to Cry1Ie as were ACB-BtS larvae, indicating no cross-resistance between Cry1Ie and Cry1Ab or Cry1Ac toxins; this may provide considerable benefits in preventing or delaying the evolution of resistance in ACB to Cry1Ab and Cry1Ac toxins. Backcrossing studies indicated that resistance to Cry1Ab toxin was polygenic in ACB-AbR, but monogenic in ACB-AcR, whilst resistance to Cry1Ac toxin was primarily monogenic in both ACB-AbR and ACB-AcR, but polygenic as resistance increased. Full article
(This article belongs to the Special Issue <i>Bacillus thuringiensis</i> Toxins)
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Open AccessArticle The Correlation of the Presence and Expression Levels of cry Genes with the Insecticidal Activities against Plutella xylostella for Bacillus thuringiensis Strains
Toxins 2014, 6(8), 2453-2470; doi:10.3390/toxins6082453
Received: 23 April 2014 / Revised: 11 August 2014 / Accepted: 11 August 2014 / Published: 19 August 2014
Cited by 1 | PDF Full-text (971 KB) | HTML Full-text | XML Full-text
Abstract
The use of Bacillus thuringiensis (Bt) strains with high insecticidal activity is essential for the preparation of bioinsecticide. In this study, for 60 Bt strains isolated in Taiwan, their genotypes and the correlation of some cry genes as well as the
[...] Read more.
The use of Bacillus thuringiensis (Bt) strains with high insecticidal activity is essential for the preparation of bioinsecticide. In this study, for 60 Bt strains isolated in Taiwan, their genotypes and the correlation of some cry genes as well as the expression levels of cry1 genes, with their insecticidal activities against Plutella xylostella, were investigated. Pulsed field gel electrophoresis (PFGE) and random amplified polymorphic DNA (RAPD) results revealed that the genotypes of these Bt strains are highly diversified. Also, a considerable number of the Bt strains isolated in Taiwan were found to have high insecticidal activities. Since strains that showed individual combined patterns of PFGE and RAPD exhibited distinct insecticidal activities against P. xylostella, thus, these genotypes may be useful for the identification of the new Bt strains and those which have been used in bioinsecticides. In addition, although the presence of cry2Aa1 may have a greater effect on the insecticidal activity of Bt strains in bioassay than other cry genes, only high expression level of cry1 genes plays a key role to determine the insecticidal activity of Bt strains. In conclusion, both RAPD and PFGE are effective in the differentiation of Bt strains. The presence of cry2Aa1 and, especially, the expression level of cry1 genes are useful for the prediction of the insecticidal activities of Bt strains against P. xylostella. Full article
(This article belongs to the Special Issue <i>Bacillus thuringiensis</i> Toxins)
Open AccessArticle Toxicity of Parasporin-4 and Health Effects of Pro-parasporin-4 Diet in Mice
Toxins 2014, 6(7), 2115-2126; doi:10.3390/toxins6072115
Received: 4 May 2014 / Revised: 23 June 2014 / Accepted: 8 July 2014 / Published: 16 July 2014
Cited by 1 | PDF Full-text (1126 KB) | HTML Full-text | XML Full-text
Abstract
Parasporin-4 (PS4) is an aerolysin-type β-pore-forming toxin produced by Bacillus thuringiensis strain A1470. It exhibits specific cytotoxicity against human cancer cell lines; therefore, it is expected to be useful for the diagnosis and treatment of particular types of cancer cells. We examined the
[...] Read more.
Parasporin-4 (PS4) is an aerolysin-type β-pore-forming toxin produced by Bacillus thuringiensis strain A1470. It exhibits specific cytotoxicity against human cancer cell lines; therefore, it is expected to be useful for the diagnosis and treatment of particular types of cancer cells. We examined the acute toxicity of PS4 on ICR mice. The LD50 value was 160 μg/kg by a subcutaneous route. Potassium, ammonium, magnesium ion, creatinine, and urea nitrogen decreased in urine by the injection of PS4. Simultaneously, creatinine and urea nitrogen in mice serum increased. These results imply that PS4 impairs kidney function in mice. PS4 is obtained from Pro-parasporin-4 (ProPS4) by processing, and ProPS4 is produced by recombinant Escherichia coli as the inclusion body. The inclusion body of ProPS4 can be solubilized in a weak acid solution and activated by pepsin, implying that it would be solubilized and activated in the stomach of mammals after oral administration. Thus, the influence of the oral administration of it by C57BL/6J mice was examined. Although ProPS4 was activated to PS4 in the mouse digestive tract, any serious health hazard was not observed and there was no significant difference in body weight change. Full article
(This article belongs to the Special Issue <i>Bacillus thuringiensis</i> Toxins)
Open AccessArticle Identification of Distinct Bacillus thuringiensis 4A4 Nematicidal Factors Using the Model Nematodes Pristionchus pacificus and Caenorhabditis elegans
Toxins 2014, 6(7), 2050-2063; doi:10.3390/toxins6072050
Received: 14 April 2014 / Revised: 2 June 2014 / Accepted: 27 June 2014 / Published: 14 July 2014
Cited by 6 | PDF Full-text (1116 KB) | HTML Full-text | XML Full-text
Abstract
Bacillus thuringiensis has been extensively used for the biological control of insect pests. Nematicidal B. thuringiensis strains have also been identified; however, virulence factors of such strains are poorly investigated. Here, we describe virulence factors of the nematicidal B. thuringiensis 4A4 strain, using
[...] Read more.
Bacillus thuringiensis has been extensively used for the biological control of insect pests. Nematicidal B. thuringiensis strains have also been identified; however, virulence factors of such strains are poorly investigated. Here, we describe virulence factors of the nematicidal B. thuringiensis 4A4 strain, using the model nematodes Pristionchus pacificus and Caenorhabditis elegans. We show that B. thuringiensis 4A4 kills both nematodes via intestinal damage. Whole genome sequencing of B. thuringiensis 4A4 identified Cry21Ha, Cry1Ba, Vip1/Vip2 and β-exotoxin as potential nematicidal factors. Only Cry21Ha showed toxicity to C. elegans, while neither Cry nor Vip toxins were active against P. pacificus, when expressed in E. coli. Purified crystals also failed to intoxicate P. pacificus, while autoclaved spore-crystal mixture of B. thuringiensis 4A4 retained toxicity, suggesting that primary β-exotoxin is responsible for P. pacificus killing. In support of this, we found that a β-exotoxin-deficient variant of B. thuringiensis 4A4, generated by plasmid curing lost virulence to the nematodes. Thus, using two model nematodes we revealed virulence factors of the nematicidal strain B. thuringiensis 4A4 and showed the multifactorial nature of its virulence. Full article
(This article belongs to the Special Issue <i>Bacillus thuringiensis</i> Toxins)
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Open AccessArticle Cloning and Characterization of a Unique Cytotoxic Protein Parasporin-5 Produced by Bacillus thuringiensis A1100 Strain
Toxins 2014, 6(6), 1882-1895; doi:10.3390/toxins6061882
Received: 28 April 2014 / Revised: 29 May 2014 / Accepted: 9 June 2014 / Published: 18 June 2014
Cited by 5 | PDF Full-text (382 KB) | HTML Full-text | XML Full-text
Abstract
Parasporin is the cytocidal protein present in the parasporal inclusion of the non-insecticidal Bacillus thuringiensis strains, which has no hemolytic activity but has cytocidal activities, preferentially killing cancer cells. In this study, we characterized a cytocidal protein that belongs to this category, which
[...] Read more.
Parasporin is the cytocidal protein present in the parasporal inclusion of the non-insecticidal Bacillus thuringiensis strains, which has no hemolytic activity but has cytocidal activities, preferentially killing cancer cells. In this study, we characterized a cytocidal protein that belongs to this category, which was designated parasporin-5 (PS5). PS5 was purified from B. thuringiensis serovar tohokuensis strain A1100 based on its cytocidal activity against human leukemic T cells (MOLT-4). The 50% effective concentration (EC50) of PS5 to MOLT-4 cells was approximately 0.075 μg/mL. PS5 was expressed as a 33.8-kDa inactive precursor protein and exhibited cytocidal activity only when degraded by protease at the C-terminal into smaller molecules of 29.8 kDa. Although PS5 showed no significant homology with other known parasporins, a Position Specific Iterative-Basic Local Alignment Search Tool (PSI-BLAST) search revealed that the protein showed slight homology to, not only some B. thuringiensis Cry toxins, but also to aerolysin-type β-pore-forming toxins (β-PFTs). The recombinant PS5 protein could be obtained as an active protein only when it was expressed in a precursor followed by processing with proteinase K. The cytotoxic activities of the protein against various mammalian cell lines were evaluated. PS5 showed strong cytocidal activity to seven of 18 mammalian cell lines tested, and low to no cytotoxicity to the others. Full article
(This article belongs to the Special Issue <i>Bacillus thuringiensis</i> Toxins)
Open AccessArticle Requirement of Simultaneous Assessment of Crystal- and Supernatant-Related Entomotoxic Activities of Bacillus thuringiensis Strains for Biocontrol-Product Development
Toxins 2014, 6(5), 1598-1614; doi:10.3390/toxins6051598
Received: 6 February 2014 / Revised: 29 April 2014 / Accepted: 12 May 2014 / Published: 20 May 2014
Cited by 1 | PDF Full-text (358 KB) | HTML Full-text | XML Full-text
Abstract
Bioinsecticides with lower concentrations of endospores/crystals and without loss of efficiency are economically advantageous for pest biocontrol. In addition to Cry proteins, other Bacillus thuringiensis (Bt) toxins in culture supernatants (SN) have biocontrol potential (e.g., Vip3A, Cry1I, Sip1), whereas others are
[...] Read more.
Bioinsecticides with lower concentrations of endospores/crystals and without loss of efficiency are economically advantageous for pest biocontrol. In addition to Cry proteins, other Bacillus thuringiensis (Bt) toxins in culture supernatants (SN) have biocontrol potential (e.g., Vip3A, Cry1I, Sip1), whereas others are unwanted (β-exotoxins), as they display widespread toxicity across taxa. A strain simultaneously providing distinct toxin activities in crystals and SN would be desirable for bioinsecticides development; however, strains secreting β-exotoxins should be discarded, independently of other useful entomotoxins. Entomotoxicity of crystals and SN from a Brazilian Bt tolworthi strain (Btt01) was tested against Spodoptera frugiperda to assess the potential for biocontrol-product development based on more than one type of toxin/activity. Tests showed that 107 endospores mL−1 caused >80% of larvae mortality, suggesting Btt01 may be used in similar concentrations as those of other Bt-based biopesticides. When it was applied to cornfields, a significant 60% reduction of larvae infestation was observed. However, bioassays with Btt01 SN revealed a thermostable toxic activity. Physicochemical characterization strongly suggests the presence of unwanted β-exotoxins, with isolate-specific temporal variation in its secretion. Knowledge of the temporal pattern of secretion/activity in culture for all forms of toxins produced by a single strain is required to both detect useful activities and avoid the potential lack of identification of undesirable toxins. These findings are discussed in the contexts of commercial Bt product development, advantages of multiple-activity strains, and care and handling recommended for large-scale fermentation systems. Full article
(This article belongs to the Special Issue <i>Bacillus thuringiensis</i> Toxins)
Open AccessArticle Draft Genome Sequences of Two Bacillus thuringiensis Strains and Characterization of a Putative 41.9-kDa Insecticidal Toxin
Toxins 2014, 6(5), 1490-1504; doi:10.3390/toxins6051490
Received: 19 February 2014 / Revised: 21 April 2014 / Accepted: 24 April 2014 / Published: 30 April 2014
Cited by 6 | PDF Full-text (767 KB) | HTML Full-text | XML Full-text
Abstract
In this work, we report the genome sequencing of two Bacillus thuringiensis strains using Illumina next-generation sequencing technology (NGS). Strain Hu4-2, toxic to many lepidopteran pest species and to some mosquitoes, encoded genes for two insecticidal crystal (Cry) proteins, cry1Ia and cry9Ea,
[...] Read more.
In this work, we report the genome sequencing of two Bacillus thuringiensis strains using Illumina next-generation sequencing technology (NGS). Strain Hu4-2, toxic to many lepidopteran pest species and to some mosquitoes, encoded genes for two insecticidal crystal (Cry) proteins, cry1Ia and cry9Ea, and a vegetative insecticidal protein (Vip) gene, vip3Ca2. Strain Leapi01 contained genes coding for seven Cry proteins (cry1Aa, cry1Ca, cry1Da, cry2Ab, cry9Ea and two cry1Ia gene variants) and a vip3 gene (vip3Aa10). A putative novel insecticidal protein gene 1143 bp long was found in both strains, whose sequences exhibited 100% nucleotide identity. The predicted protein showed 57 and 100% pairwise identity to protein sequence 72 from a patented Bt strain (US8318900) and to a putative 41.9-kDa insecticidal toxin from Bacillus cereus, respectively. The 41.9-kDa protein, containing a C-terminal 6× HisTag fusion, was expressed in Escherichia coli and tested for the first time against four lepidopteran species (Mamestra brassicae, Ostrinia nubilalis, Spodoptera frugiperda and S. littoralis) and the green-peach aphid Myzus persicae at doses as high as 4.8 µg/cm2 and 1.5 mg/mL, respectively. At these protein concentrations, the recombinant 41.9-kDa protein caused no mortality or symptoms of impaired growth against any of the insects tested, suggesting that these species are outside the protein’s target range or that the protein may not, in fact, be toxic. While the use of the polymerase chain reaction has allowed a significant increase in the number of Bt insecticidal genes characterized to date, novel NGS technologies promise a much faster, cheaper and efficient screening of Bt pesticidal proteins. Full article
(This article belongs to the Special Issue <i>Bacillus thuringiensis</i> Toxins)
Open AccessArticle Changes in Gene Expression in the Larval Gut of Ostrinia nubilalis in Response to Bacillus thuringiensis Cry1Ab Protoxin Ingestion
Toxins 2014, 6(4), 1274-1294; doi:10.3390/toxins6041274
Received: 11 December 2013 / Revised: 13 March 2014 / Accepted: 26 March 2014 / Published: 3 April 2014
Cited by 6 | PDF Full-text (586 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
We developed a microarray based on 2895 unique transcripts assembled from 15,000 cDNA sequences from the European corn borer (Ostrinia nubilalis) larval gut. This microarray was used to monitor gene expression in early third-instar larvae of Bacillus thuringiensis (Bt)-susceptible O. nubilalis
[...] Read more.
We developed a microarray based on 2895 unique transcripts assembled from 15,000 cDNA sequences from the European corn borer (Ostrinia nubilalis) larval gut. This microarray was used to monitor gene expression in early third-instar larvae of Bacillus thuringiensis (Bt)-susceptible O. nubilalis after 6 h feeding on diet, with or without the Bt Cry1Ab protoxin. We identified 174 transcripts, for which the expression was changed more than two-fold in the gut of the larvae fed Cry1Ab protoxin (p < 0.05), representing 80 down-regulated and 94 up-regulated transcripts. Among 174 differentially expressed transcripts, 13 transcripts putatively encode proteins that are potentially involved in Bt toxicity, and these transcripts include eight serine proteases, three aminopeptidases, one alkaline phosphatase, and one cadherin. The expressions of trypsin-like protease and three aminopeptidase transcripts were variable, but two potential Bt-binding proteins, alkaline phosphatase and cadherin were consistently up-regulated in larvae fed Cry1Ab protoxin. The significantly up and down-regulated transcripts may be involved in Cry1Ab toxicity by activation, degradation, toxin binding, and other related cellular responses. This study is a preliminary survey of Cry1Ab protoxin-induced transcriptional responses in O. nubilalis gut and our results are expected to help with further studies on Bt toxin-insect interactions at the molecular level. Full article
(This article belongs to the Special Issue <i>Bacillus thuringiensis</i> Toxins)
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Review

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Open AccessReview Bacillus thuringiensis Toxins: An Overview of Their Biocidal Activity
Toxins 2014, 6(12), 3296-3325; doi:10.3390/toxins6123296
Received: 1 September 2014 / Revised: 7 November 2014 / Accepted: 3 December 2014 / Published: 11 December 2014
Cited by 28 | PDF Full-text (793 KB) | HTML Full-text | XML Full-text
Abstract
Bacillus thuringiensis (Bt) is a Gram positive, spore-forming bacterium that synthesizes parasporal crystalline inclusions containing Cry and Cyt proteins, some of which are toxic against a wide range of insect orders, nematodes and human-cancer cells. These toxins have been successfully used as bioinsecticides
[...] Read more.
Bacillus thuringiensis (Bt) is a Gram positive, spore-forming bacterium that synthesizes parasporal crystalline inclusions containing Cry and Cyt proteins, some of which are toxic against a wide range of insect orders, nematodes and human-cancer cells. These toxins have been successfully used as bioinsecticides against caterpillars, beetles, and flies, including mosquitoes and blackflies. Bt also synthesizes insecticidal proteins during the vegetative growth phase, which are subsequently secreted into the growth medium. These proteins are commonly known as vegetative insecticidal proteins (Vips) and hold insecticidal activity against lepidopteran, coleopteran and some homopteran pests. A less well characterized secretory protein with no amino acid similarity to Vip proteins has shown insecticidal activity against coleopteran pests and is termed Sip (secreted insecticidal protein). Bin-like and ETX_MTX2-family proteins (Pfam PF03318), which share amino acid similarities with mosquitocidal binary (Bin) and Mtx2 toxins, respectively, from Lysinibacillus sphaericus, are also produced by some Bt strains. In addition, vast numbers of Bt isolates naturally present in the soil and the phylloplane also synthesize crystal proteins whose biological activity is still unknown. In this review, we provide an updated overview of the known active Bt toxins to date and discuss their activities. Full article
(This article belongs to the Special Issue <i>Bacillus thuringiensis</i> Toxins)
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Open AccessReview Bt Toxin Modification for Enhanced Efficacy
Toxins 2014, 6(10), 3005-3027; doi:10.3390/toxins6103005
Received: 2 May 2014 / Revised: 28 September 2014 / Accepted: 29 September 2014 / Published: 22 October 2014
Cited by 6 | PDF Full-text (790 KB) | HTML Full-text | XML Full-text
Abstract
Insect-specific toxins derived from Bacillus thuringiensis (Bt) provide a valuable resource for pest suppression. Here we review the different strategies that have been employed to enhance toxicity against specific target species including those that have evolved resistance to Bt, or to modify the
[...] Read more.
Insect-specific toxins derived from Bacillus thuringiensis (Bt) provide a valuable resource for pest suppression. Here we review the different strategies that have been employed to enhance toxicity against specific target species including those that have evolved resistance to Bt, or to modify the host range of Bt crystal (Cry) and cytolytic (Cyt) toxins. These strategies include toxin truncation, modification of protease cleavage sites, domain swapping, site-directed mutagenesis, peptide addition, and phage display screens for mutated toxins with enhanced activity. Toxin optimization provides a useful approach to extend the utility of these proteins for suppression of pests that exhibit low susceptibility to native Bt toxins, and to overcome field resistance. Full article
(This article belongs to the Special Issue <i>Bacillus thuringiensis</i> Toxins)
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Open AccessReview Structural Insights into Bacillus thuringiensis Cry, Cyt and Parasporin Toxins
Toxins 2014, 6(9), 2732-2770; doi:10.3390/toxins6092732
Received: 29 April 2014 / Revised: 26 August 2014 / Accepted: 28 August 2014 / Published: 16 September 2014
Cited by 12 | PDF Full-text (3204 KB) | HTML Full-text | XML Full-text
Abstract
Since the first X-ray structure of Cry3Aa was revealed in 1991, numerous structures of B. thuringiensis toxins have been determined and published. In recent years, functional studies on the mode of action and resistance mechanism have been proposed, which notably promoted the developments
[...] Read more.
Since the first X-ray structure of Cry3Aa was revealed in 1991, numerous structures of B. thuringiensis toxins have been determined and published. In recent years, functional studies on the mode of action and resistance mechanism have been proposed, which notably promoted the developments of biological insecticides and insect-resistant transgenic crops. With the exploration of known pore-forming toxins (PFTs) structures, similarities between PFTs and B. thuringiensis toxins have provided great insights into receptor binding interactions and conformational changes from water-soluble to membrane pore-forming state of B. thuringiensis toxins. This review mainly focuses on the latest discoveries of the toxin working mechanism, with the emphasis on structural related progress. Based on the structural features, B. thuringiensis Cry, Cyt and parasporin toxins could be divided into three categories: three-domain type α-PFTs, Cyt toxin type β-PFTs and aerolysin type β-PFTs. Structures from each group are elucidated and discussed in relation to the latest data, respectively. Full article
(This article belongs to the Special Issue <i>Bacillus thuringiensis</i> Toxins)
Open AccessReview Molecular Approaches to Improve the Insecticidal Activity of Bacillus thuringiensis Cry Toxins
Toxins 2014, 6(8), 2393-2423; doi:10.3390/toxins6082393
Received: 14 May 2014 / Revised: 23 June 2014 / Accepted: 27 June 2014 / Published: 13 August 2014
Cited by 3 | PDF Full-text (7741 KB) | HTML Full-text | XML Full-text
Abstract
Bacillus thuringiensis (Bt) is a gram-positive spore-forming soil bacterium that is distributed worldwide. Originally recognized as a pathogen of the silkworm, several strains were found on epizootic events in insect pests. In the 1960s, Bt began to be successfully used to control insect
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Bacillus thuringiensis (Bt) is a gram-positive spore-forming soil bacterium that is distributed worldwide. Originally recognized as a pathogen of the silkworm, several strains were found on epizootic events in insect pests. In the 1960s, Bt began to be successfully used to control insect pests in agriculture, particularly because of its specificity, which reflects directly on their lack of cytotoxicity to human health, non-target organisms and the environment. Since the introduction of transgenic plants expressing Bt genes in the mid-1980s, numerous methodologies have been used to search for and improve toxins derived from native Bt strains. These improvements directly influence the increase in productivity and the decreased use of chemical insecticides on Bt-crops. Recently, DNA shuffling and in silico evaluations are emerging as promising tools for the development and exploration of mutant Bt toxins with enhanced activity against target insect pests. In this report, we describe natural and in vitro evolution of Cry toxins, as well as their relevance in the mechanism of action for insect control. Moreover, the use of DNA shuffling to improve two Bt toxins will be discussed together with in silico analyses of the generated mutations to evaluate their potential effect on protein structure and cytotoxicity. Full article
(This article belongs to the Special Issue <i>Bacillus thuringiensis</i> Toxins)
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Open AccessReview Quorum Sensing in Bacillus thuringiensis Is Required for Completion of a Full Infectious Cycle in the Insect
Toxins 2014, 6(8), 2239-2255; doi:10.3390/toxins6082239
Received: 29 May 2014 / Revised: 10 July 2014 / Accepted: 15 July 2014 / Published: 31 July 2014
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Abstract
Bacterial cell-cell communication or quorum sensing (QS) is a biological process commonly described as allowing bacteria belonging to a same pherotype to coordinate gene expression to cell density. In Gram-positive bacteria, cell-cell communication mainly relies on cytoplasmic sensors regulated by secreted and re-imported
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Bacterial cell-cell communication or quorum sensing (QS) is a biological process commonly described as allowing bacteria belonging to a same pherotype to coordinate gene expression to cell density. In Gram-positive bacteria, cell-cell communication mainly relies on cytoplasmic sensors regulated by secreted and re-imported signaling peptides. The Bacillus quorum sensors Rap, NprR, and PlcR were previously identified as the first members of a new protein family called RNPP. Except for the Rap proteins, these RNPP regulators are transcription factors that directly regulate gene expression. QS regulates important biological functions in bacteria of the Bacillus cereus group. PlcR was first characterized as the main regulator of virulence in B. thuringiensis and B. cereus. More recently, the PlcR-like regulator PlcRa was characterized for its role in cysteine metabolism and in resistance to oxidative stress. The NprR regulator controls the necrotrophic properties allowing the bacteria to survive in the infected host. The Rap proteins negatively affect sporulation via their interaction with a phosphorelay protein involved in the activation of Spo0A, the master regulator of this differentiation pathway. In this review we aim at providing a complete picture of the QS systems that are sequentially activated during the lifecycle of B. cereus and B. thuringiensis in an insect model of infection. Full article
(This article belongs to the Special Issue <i>Bacillus thuringiensis</i> Toxins)
Open AccessReview Thuringiensin: A Thermostable Secondary Metabolite from Bacillus thuringiensis with Insecticidal Activity against a Wide Range of Insects
Toxins 2014, 6(8), 2229-2238; doi:10.3390/toxins6082229
Received: 14 April 2014 / Revised: 16 July 2014 / Accepted: 18 July 2014 / Published: 25 July 2014
Cited by 7 | PDF Full-text (871 KB) | HTML Full-text | XML Full-text
Abstract
Thuringiensin (Thu), also known as β-exotoxin, is a thermostable secondary metabolite secreted by Bacillus thuringiensis. It has insecticidal activity against a wide range of insects, including species belonging to the orders Diptera, Coleoptera, Lepidoptera, Hymenoptera, Orthoptera, and Isoptera, and several nematode species.
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Thuringiensin (Thu), also known as β-exotoxin, is a thermostable secondary metabolite secreted by Bacillus thuringiensis. It has insecticidal activity against a wide range of insects, including species belonging to the orders Diptera, Coleoptera, Lepidoptera, Hymenoptera, Orthoptera, and Isoptera, and several nematode species. The chemical formula of Thu is C22H32O19N5P, and it is composed of adenosine, glucose, phosphoric acid, and gluconic diacid. In contrast to the more frequently studied insecticidal crystal protein, Thu is not a protein but a small molecule oligosaccharide. In this review, a detailed and updated description of the characteristics, structure, insecticidal mechanism, separation and purification technology, and genetic determinants of Thu is provided. Full article
(This article belongs to the Special Issue <i>Bacillus thuringiensis</i> Toxins)
Open AccessReview Regulation of cry Gene Expression in Bacillus thuringiensis
Toxins 2014, 6(7), 2194-2209; doi:10.3390/toxins6072194
Received: 3 June 2014 / Revised: 11 July 2014 / Accepted: 15 July 2014 / Published: 23 July 2014
Cited by 3 | PDF Full-text (777 KB) | HTML Full-text | XML Full-text
Abstract
Bacillus thuringiensis differs from the closely related Bacillus cereus group species by its ability to produce crystalline inclusions. The production of these crystals mainly results from the expression of the cry genes, from the stability of their transcripts and from the synthesis, accumulation
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Bacillus thuringiensis differs from the closely related Bacillus cereus group species by its ability to produce crystalline inclusions. The production of these crystals mainly results from the expression of the cry genes, from the stability of their transcripts and from the synthesis, accumulation and crystallization of large amounts of insecticidal Cry proteins. This process normally coincides with sporulation and is regulated by various factors operating at the transcriptional, post-transcriptional, metabolic and post-translational levels. Full article
(This article belongs to the Special Issue <i>Bacillus thuringiensis</i> Toxins)
Open AccessReview Bacillus thuringiensis subsp. israelensis and Its Dipteran-Specific Toxins
Toxins 2014, 6(4), 1222-1243; doi:10.3390/toxins6041222
Received: 28 January 2014 / Revised: 10 March 2014 / Accepted: 14 March 2014 / Published: 28 March 2014
Cited by 23 | PDF Full-text (379 KB) | HTML Full-text | XML Full-text
Abstract
Bacillus thuringiensis subsp. israelensis (Bti) is the first Bacillus thuringiensis to be found and used as an effective biological control agent against larvae of many mosquito and black fly species around the world. Its larvicidal activity resides in four major (of
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Bacillus thuringiensis subsp. israelensis (Bti) is the first Bacillus thuringiensis to be found and used as an effective biological control agent against larvae of many mosquito and black fly species around the world. Its larvicidal activity resides in four major (of 134, 128, 72 and 27 kDa) and at least two minor (of 78 and 29 kDa) polypeptides encoded respectively by cry4Aa, cry4Ba, cry11Aa, cyt1Aa, cry10Aa and cyt2Ba, all mapped on the 128 kb plasmid known as pBtoxis. These six δ-endotoxins form a complex parasporal crystalline body with remarkably high, specific and different toxicities to Aedes, Culex and Anopheles larvae. Cry toxins are composed of three domains (perforating domain I and receptor binding II and III) and create cation-selective channels, whereas Cyts are composed of one domain that acts as well as a detergent-like membrane perforator. Despite the low toxicities of Cyt1Aa and Cyt2Ba alone against exposed larvae, they are highly synergistic with the Cry toxins and hence their combinations prevent emergence of resistance in the targets. The lack of significant levels of resistance in field mosquito populations treated for decades with Bti-bioinsecticide suggests that this bacterium will be an effective biocontrol agent for years to come. Full article
(This article belongs to the Special Issue <i>Bacillus thuringiensis</i> Toxins)

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Open AccessReply Response to Leopoldo Palma. Comments on Ekino et al. Cloning and Characterization of a Unique Cytotoxic Protein Parasporin-5 Produced by Bacillus thuringiensis A1100 Strain. Toxins 2014, 6, 1882–1895
Toxins 2015, 7(12), 5096-5097; doi:10.3390/toxins7124866
Received: 18 November 2015 / Accepted: 19 November 2015 / Published: 27 November 2015
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Abstract I appreciate the thoughtful comments from Dr. Leopoldo Palma [1] on our research about cytotoxic protein parasporin-5 produced by Bacillus thuringiensis (BT) A1100 strain [2]. [...] Full article
(This article belongs to the Special Issue <i>Bacillus thuringiensis</i> Toxins)
Open AccessComment Comments on Ekino et al. Cloning and Characterization of a Unique Cytotoxic Protein Parasporin-5 Produced by Bacillus thuringiensis A1100 Strain. Toxins 2014, 6, 1882–1895
Toxins 2015, 7(12), 5094-5095; doi:10.3390/toxins7124865
Received: 17 September 2015 / Accepted: 18 November 2015 / Published: 27 November 2015
Cited by 1 | PDF Full-text (149 KB) | HTML Full-text | XML Full-text
Abstract Ekino et al. [1] reported the cloning and characterization of a novel cytotoxic protein (Parasporin-5) produced by Bacillus thuringiensis strain A1100. [...] Full article
(This article belongs to the Special Issue <i>Bacillus thuringiensis</i> Toxins)
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