Search results for "Bacillus thuringiensi"
showing 10 items of 213 documents
Insecticidal Activity and Synergistic Combinations of Ten Different Bt Toxins against Mythimna separata (Walker)
2018
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
Functional significance of membrane associated proteolysis in the toxicity of Bacillus thuringiensis Cry3Aa toxin against Colorado potato beetle.
2012
Abstract Bacillus thuringiensis Cry toxins are widely used as biocontrol agents in bioinsecticides and transgenic plants. In the three domain-Cry toxins, domain II has been identified as an important determinant of their highly specific activity against insects. In this work, we assessed the role in membrane associated proteolysis and toxicity in Colorado potato beetle (CPB) of a previously reported ADAM recognition motif present in Cry3Aa toxin domain II. We used site-directed mutagenesis to modify the Bacillus thuringiensis cry3A gene in amino acid residues 344, 346, 347, 351 and 353 of the ADAM recognition motif in Cry3Aa toxin. Cry3Aa toxin mutants displayed decreased toxicity when comp…
Mode of action of Bacillus thuringiensis PS86Q3 strain in hymenopteran forest pests
2001
The mode of action of Cry toxins has been described principally in lepidopteran insects as a multistep process. In this work we describe the mode of action of a Cry toxin active in the common pine sawfly Diprion pini (Hymenoptera, Diprionidae), considered a major forest pest in Europe. Strain PS86Q3 contains a long bipyramidal crystal composed of five major proteins. The N-terminal sequence shows that the 155 kDa protein corresponds to Cry5B toxin and the other proteins belong to the Cry5A subgroup. PCR analysis indicates the presence of cry5Ac and cry5Ba genes, suggesting that Cry5A protein should be Cry5Ac. Activation of protoxins with trypsin or with midgut content from D. pini and Cepha…
Lyophilization of lepidopteran midguts: a preserving method for Bacillus thuringiensis toxin binding studies
2004
Binding assays with brush border membrane vesicles (BBMV) from insect midguts are commonly used in the study of the interactions between Bacillus thuringiensis Cry toxins and their receptors. Collaboration between laboratories often require that frozen insect samples are sent in dry ice. Because of customs restrictions and delays, sample thawing is always a risk and often the biological material becomes ruined during shipping. We have tested lyophilization as an alternative method for preserving insect midguts for binding studies with B. thuringiensis Cry toxins. For this purpose, BBMV were prepared from both frozen and lyophilized midguts from three lepidopteran species: Spodoptera exigua,…
Biochemistry and genetics of insect resistance toBacillus thuringiensisinsecticidal crystal proteins
1995
Current knowledge of biochemical mechanisms of insect resistance to Bacillus thuringiensis is reviewed. Available information on resistance inheritance and on patterns of cross-resistance is included. Modification of the binding sites for B. thuringiensis insecticidal crystal proteins has been found in different populations of three insect species. This resistance mechanism seems to be inherited as a single recessive or partially recessive major gene, and the resistance levels reached are high. Altered proteolytic processing of B. thuringiensis crystal proteins has been suggested to be involved in one case of resistance. From the available data it seems that binding site modification is the…
Study of the aminopeptidase N gene family in the lepidopterans Ostrinia nubilalis (Hübner) and Bombyx mori (L.): Sequences, mapping and expression
2010
Aminopeptidases N (APNs) are a class of ectoenzymes present in lepidopteran larvae midguts, involved in the Bacillus thuringiensis (Bt) toxins mode of action. In the present work, seven aminopeptidases have been cloned from the midgut of Ostrinia nubilalis, the major Lepidopteran corn pest in the temperate climates. Six sequences were identified as APNs because of the presence of the HEXXH(X)18E and GAMEN motifs, as well as the signal peptide and the GPI-anchor sequences. The remaining sequence did not contain the two cellular targeting signals, indicating it belonged to the puromycin-sensitive aminopeptidase (PSA) family. An in silico analysis allowed us to find orthologous sequences in Bo…
Hetero-oligomerization of Bacillus thuringiensis Cry1A proteins enhance binding to the ABCC2 transporter of Spodoptera exigua
2021
The ATP binding cassette (ABC) transporters are membrane proteins that can act as putative receptors for Cry proteins from Bacillus thuringiensis (Bt) in the midgut of different insects. For the beet armyworm, Spodoptera exigua, ABCC2 and ABCC3 have been found to interact with Cry1A proteins, the main insecticidal proteins used in Bt crops, as well as Bt-based pesticides. The ABCC2 has shown to have specific binding towards Cry1Ac and is involved in the toxic process of Cry1A proteins, but the role of this transporter and how it relates with the Cry1A proteins is still unknown. Here, we have characterized the interactions between the SeABCC2 and the main proteins that bind to the receptor. …
Genetic variability of Spodoptera frugiperda Smith (Lepidoptera: Noctuidae) populations from Latin America is associated with variations in susceptib…
2006
ABSTRACT Bacillus thuringiensis strains isolated from Latin American soil samples that showed toxicity against three Spodoptera frugiperda populations from different geographical areas (Mexico, Colombia, and Brazil) were characterized on the basis of their insecticidal activity, crystal morphology, sodium dodecyl sulfate-polyacrylamide gel electrophoresis of parasporal crystals, plasmid profiles, and cry gene content. We found that the different S. frugiperda populations display different susceptibilities to the selected B. thuringiensis strains and also to pure preparations of Cry1B, Cry1C, and Cry1D toxins. Binding assays performed with pure toxin demonstrated that the differences in the …
Trans-generational immune priming in the mealworm beetle protects eggs through pathogen-dependent mechanisms imposing no immediate fitness cost for t…
2018
8 pages; International audience; Immune-challenged mothers can improve their offspring immunity through trans-generational immune priming (TGIP). In insects, TGIP endows the offspring with lifetime immunity, including the eggs, which are likely exposed soon after maternal infection. Egg protection may rely on the transfer of maternal immune effectors to the egg or/and the induction of egg immune genes. These respective mechanisms are assumed to have early-life fitness costs of different magnitude for the offspring. We provide evidence in the mealworm beetle Tenebrio molitor that enhanced egg immunity following a maternal immune challenge is achieved by both of these mechanisms but in a path…
Binding Site Alteration Is Responsible for Field-Isolated Resistance to Bacillus thuringiensis Cry2A Insecticidal Proteins in Two Helicoverpa Species
2010
Background Evolution of resistance by target pests is the main threat to the long-term efficacy of crops expressing Bacillus thuringiensis (Bt) insecticidal proteins. Cry2 proteins play a pivotal role in current Bt spray formulations and transgenic crops and they complement Cry1A proteins because of their different mode of action. Their presence is critical in the control of those lepidopteran species, such as Helicoverpa spp., which are not highly susceptible to Cry1A proteins. In Australia, a transgenic variety of cotton expressing Cry1Ac and Cry2Ab (Bollgard II) comprises at least 80% of the total cotton area. Prior to the widespread adoption of Bollgard II, the frequency of alleles conf…