Mode of action of mosquitocidal Bacillus thuringiensis toxins

Soberón, Mário; Fernández, Luisa Elena; Pérez, Cirilo; Gill, Sarjeet S.; Bravo, Alejandra

doi:10.1016/j.toxicon.2006.11.008

Cited by 65 publications

(51 citation statements)

References 17 publications

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“…Specific binding is the crucial step in the mode of action for the exquisite specificity of Cry proteins (46), and binding site alteration on midgut cells is the main mechanism conferring high levels of resistance to Cry proteins in insect populations (15,16). There is strong evidence that, after binding, Cry1A proteins form oligomers which insert into the midgut epithelium, causing cell lysis (8,42), though the involvement of a signaling pathway has also been proposed (48,49).…”

Section: Homologous-competition Assays Withmentioning

confidence: 99%

Specific Binding of Bacillus thuringiensis Cry2A Insecticidal Proteins to a Common Site in the Midgut of Helicoverpa Species

Hernández‐Rodríguez

Vliet

Bautsoens

et al. 2008

Appl Environ Microbiol

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For a long time, it has been assumed that the mode of action of Cry2A toxins was unique and different from that of other three-domain Cry toxins due to their apparent nonspecific and unsaturable binding to an unlimited number of receptors. However, based on the homology of the tertiary structure among three-domain Cry toxins, similar modes of action for all of them are expected. To confirm this hypothesis, binding assays were carried out with 125 I-labeled Cry2Ab. Saturation assays showed that Cry2Ab binds in a specific and saturable manner to brush border membrane vesicles (BBMVs) of Helicoverpa armigera. Homologous-competition assays with125 I-Cry2Ab demonstrated that this toxin binds with high affinity to binding sites in H. armigera and Helicoverpa zea midgut. Heterologous-competition assays showed a common binding site for three toxins belonging to the Cry2A family (Cry2Aa, Cry2Ab, and Cry2Ae), which is not shared by Cry1Ac. Estimation of K d (dissociation constant) values revealed that Cry2Ab had around 35-fold less affinity than Cry1Ac for BBMV binding sites in both insect species. Only minor differences were found regarding R t (concentration of binding sites) values. This study questions previous interpretations from other authors performing binding assays with Cry2A toxins and establishes the basis for the mode of action of Cry2A toxins.

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Section: Homologous-competition Assays Withmentioning

confidence: 99%

Specific Binding of Bacillus thuringiensis Cry2A Insecticidal Proteins to a Common Site in the Midgut of Helicoverpa Species

Hernández‐Rodríguez

Vliet

Bautsoens

et al. 2008

Appl Environ Microbiol

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“…israelensis (Bti) and Bacillus sphaericus (Bs) which selectively kill mosquito larvae with negligible effect to the non‐target organisms (Walker & Lynch, 2007). Susceptible mosquito larvae have alkaline gut conditions, enzymes and specific receptors for processing and binding of the Bti or Bs toxins (Baumann, Clark, Baumann, & Broadwell, 1991; Bravo, Gill, & Soberón, 2007; Dadd, 1975; Nicolas, Lecroisey, & Charles, 1990; Soberón, Fernández, Pérez, Gill, & Bravo, 2007). Thus, the toxins responsible for the pathogenic effect in mosquito larvae have no effect to vertebrates and some invertebrates, and hence they are suitable for application even in peri‐domestic mosquito breeding habitats (Lacey, 2007; Lacey & Merritt, 2003; Saik, Lacey, & Lacey, 1990).…”

Section: Introductionmentioning

confidence: 99%

Microbial larvicides for mosquito control: Impact of long lasting formulations of Bacillus thuringiensis var. israelensis and Bacillus sphaericus on non‐target organisms in western Kenya highlands

Derua

Kahindi

Mosha

et al. 2018

Ecology and Evolution

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The microbial larvicides Bacillus thuringiensis var. israelensis and Bacillus sphaericus have been used extensively for mosquito control and have been found to be effective and safe to non‐target organisms cohabiting with mosquito larvae. Recently developed long lasting microbial larvicides (LLML), although evading the previous challenge of short duration of activity, increase the risk of persistence of toxins in the treated larval habitats. This study monitored the impact of LLML FourStar® and LL3 on non‐target organisms cohabiting with mosquito larvae in an operational study to control malaria vectors in western Kenya highlands. A total of 300 larval habitats were selected in three highland villages. The habitats were first monitored for 5 weeks to collect baseline data on non‐target organisms cohabiting with mosquito larvae and then randomized into two treatment arms (respective FourStar® and LL3) and one control arm. Non‐target organisms were sampled weekly for 5 months after treatment to assess the impact of LLML intervention. Before treatment, the mean density of all non‐target organisms combined in the control, LL3 and FourStar® treated habitats was 1.42, 1.39 and 1.49 individuals per habitat per sampling occasion, respectively. Following treatment, this density remained fairly unchanged for 21 weeks at which time it was 1.82, 2.11, and 2.05 for the respective control, LL3 and FourStar® treated habitats. Statistical analysis revealed that LL3 and FourStar® did not significantly alter abundance, richness or diversity of the 11 taxa studied, when comparing the intervention and control larval habitats. However, both FourStar® and LL3 significantly reduced the density of malaria vectors. In conclusion, one round of label rate application of FourStar® or LL3 in natural larval habitats did not alter richness, abundance or diversity of the monitored aquatic non‐target organisms cohabiting with mosquito larvae to an ecologically significant level.

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“…israelensis have been widely used worldwide as a bacterial insecticide for controlling mosquito larvae (1). The high toxicity of this bacterium is mainly attributed to an arsenal of protoxins, such as Cry4Aa, Cry4Ba, Cry11Aa, and Cyt1Aa, harbored in its parasporal crystals, and their synergistic interaction.…”

mentioning

confidence: 99%

Identification and Characterization of Three Previously Undescribed Crystal Proteins from Bacillus thuringiensis subsp. jegathesan

Sun

Zhao

Xia

et al. 2013

Appl Environ Microbiol

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The total protoxin complement in the parasporal body of mosquitocidal strain, Bacillus thuringiensis subsp. jegathesan 367, was determined by use of a polyacrylamide gel block coupled to mass spectrometry. A total of eight protoxins were identified from this strain, including five reported protoxins (Cry11Ba, Cry19Aa, Cry24Aa, Cry25Aa, and Cyt2Bb), as well as three previously undescribed (Cry30Ca, Cry60Aa, and Cry60Ba) in this isolate. It was interesting that the encoding genes of three new protoxins existed as cry30Ca-gap-orf2 and cry60Ba-gap-cry60Aa. The cry30Ca and a downstream orf2 gene were oriented in the same direction and separated by 114 bp, and cry60Ba was located 156 bp upstream from and in the same orientation to cry60Aa. The three new protoxin genes were cloned from B. thuringiensis subsp. jegathesan and expressed in an acrystalliferous strain under the control of cyt1A gene promoters and the STAB-SD stabilizer sequence. Recombinant strain containing only cry30Ca did not produce visible inclusion under microscope observation, while that containing both cry30Ca and orf2 could produce large inclusions. Cry60Aa and Cry60Ba synthesized either alone or together in the acrystalliferous host could yield large inclusions. In bioassays using the fourth-instar larvae of Culex quinquefasciatus, Cry60Aa and Cry60Ba alone or together had estimated 50% lethal concentrations of 2.9 to 7.9 g/ml; however, Cry30Ca with or without ORF2 was not toxic to this mosquito.

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Mode of action of mosquitocidal Bacillus thuringiensis toxins

Cited by 65 publications

References 17 publications

Specific Binding of Bacillus thuringiensis Cry2A Insecticidal Proteins to a Common Site in the Midgut of Helicoverpa Species

Specific Binding of Bacillus thuringiensis Cry2A Insecticidal Proteins to a Common Site in the Midgut of Helicoverpa Species

Microbial larvicides for mosquito control: Impact of long lasting formulations of Bacillus thuringiensis var. israelensis and Bacillus sphaericus on non‐target organisms in western Kenya highlands

Identification and Characterization of Three Previously Undescribed Crystal Proteins from Bacillus thuringiensis subsp. jegathesan

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