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Jeanfrancois Charles - One of the best experts on this subject based on the ideXlab platform.
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transposon mediated resistance to Bacillus Sphaericus in a field evolved population of culex pipiens diptera culicidae
Cellular Microbiology, 2007Co-Authors: Isabelle Darboux, Jeanfrancois Charles, Yannick Pauchet, Sylvie Warot, David PauronAbstract:Summary The binary toxin is the major active component of Bacillus Sphaericus, a microbial larvicide used for controlling some vector mosquito-borne diseases. B. Sphaericus resistance has been reported in many part of the world, leading to a growing concern for the usefulness of this environmental friendly insecticide. Here we characterize a novel mechanism of resistance to the binary toxin in a natural population of the West Nile virus vector, Culex pipiens. We show that the insertion of a transposable element-like DNA into the coding sequence of the midgut toxin receptor induces a new mRNA splicing event, unmasking cryptic donor and acceptor sites located in the host gene. The creation of the new intron causes the expression of an altered membrane protein, which is incapable of interacting with the toxin, thus providing the host mosquito with an advantageous phenotype. As a large portion of insect genomes is composed of transposable elements or transposable elements-related sequences, this new mechanism may be of general importance to appreciate their significance as potent agents for insect resistance to the microbial insecticides.
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the receptor of Bacillus Sphaericus binary toxin in culex pipiens diptera culicidae midgut molecular cloning and expression
Insect Biochemistry and Molecular Biology, 2001Co-Authors: Isabelle Darboux, Christina Nielsenleroux, Jeanfrancois Charles, David PauronAbstract:Culex pipiens larval midgut is the primary target of the binary toxin (Bin) present in parasporal inclusions of Bacillus Sphaericus. Cpm1, a 60-kDa protein purified from brush border membranes, has been proposed as the receptor of the Bin toxin in the midgut epithelial cells of mosquitoes. We have cloned and characterized the corresponding cDNA from midgut of Culex pipiens larvae. The open reading frame predicted a 580 amino-acid protein with a putative signal peptide at the N-terminus and a putative GPI-anchoring signal at the C-terminus. The amino acid sequence of the cloned Cpm1 exhibited 39-43% identities with insect maltases (alpha-glucosidases and alpha-amylases). Recombinant Cpm1 expressed in E. coli specifically bound to the Bin toxin and had a significant alpha-glucosidase activity but no alpha-amylase activity. These results support the view that Cpm1 is an alpha-glucosidase expressed in Culex midgut where it constitutes the receptor for the Bin toxin. To date, this is the first component involved in the mosquitocidal activity of the Bacillus Sphaericus Bin toxin to be characterized. Its identification provides a key step to elucidate the mode of action of the Bin toxin and the mechanisms of resistance developed against it by some mosquito strains.
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identification of the receptor for Bacillus Sphaericus crystal toxin in the brush border membrane of the mosquito culex pipiens diptera culicidae
Insect Biochemistry and Molecular Biology, 1999Co-Authors: Mariahelena Silvafilha, Christina Nielsenleroux, Jeanfrancois CharlesAbstract:The binary toxin (Bin) from Bacillus Sphaericus crystals specifically binds to soluble midgut brush border membrane proteins from Culex pipiens larvae. A single 60 kDa midgut membrane protein is identified as the binding protein. This protein is anchored in the mosquito midgut membrane via a glycosyl-phosphatidylinositol (GPI) anchor, and is partially released by phosphatidylinositol specific-phospholipase C (PI-PLC). Fractionation of soluble proteins by anion exchange chromatography indicates that the binding protein does not co-elute with leucine aminopeptidase activity. After partial purification, the sequences of internal amino acid fragments of the 60 kDa protein were determined. The peptide sequences were compared with data in GenBank, and showed a very high degree of similarity with enzymes belonging to the alpha-amylase family. Further enzymatic investigation showed that the receptor of the Bin toxin in C. pipiens larval midgut may be an alpha-glucosidase.
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resistance to Bacillus Sphaericus involves different mechanisms in culex pipiens diptera culicidae larvae
Journal of Medical Entomology, 1997Co-Authors: Christina Nielsenleroux, Jeanfrancois Charles, Florence Pasquier, Gilbert Sinegre, Bruno Gaven, Nicole PasteurAbstract:Field Culex pipiens pipiens (L.) mosquitoes that were collected after a control failure with Spherimos in southern France developed high resistance (> 10,000-fold) to Bacillus Sphaericus crystal toxin after <8 generations of laboratory selection. We show that this resistance is encoded by a single major recessive gene on linkage group I at 22.1 recombination units from the sex locus, and that it is not associated with any loss of binding affinity between brush border membrane fractions and die B. Sphaericus radiolabeled toxin. Thus, in Southern France, resistance differs from the high B. Sphaericus resistance developed after laboratory selection of Californian C. p. quinquefasciatus. This demonstrates that at least 2 different mechanisms may confer high levels of resistance to B. Sphaericus crystal toxin in mosquitoes of the C. pipiens complex. These results have important implications for mosquito control strategies.
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low level resistance to Bacillus Sphaericus in a field treated population of culex quinquefasciatus diptera culicidae
Journal of Economic Entomology, 1995Co-Authors: Mariahelena Silvafilha, Lêda Regis, Christina Nielsenleroux, Jeanfrancois CharlesAbstract:A field-collected population of Crlex pipietls quinquefasciatus larvae from an urban area of Recife (Brazil), which has been treated for 2 yr with Bacillus Sphaericus, was found to be ≈10-fold less susceptible than control field populations. Comparative in vitro binding experiments between the radiolabeled toxin from B. Sphaericus and isolated midgut brush border membranes from the treated and the untreated larval populations, indicated no change in the affinity of the midgut receptor of the treated population for the toxin, and only a slight decrease in the receptor concentration.
Christina Nielsenleroux - One of the best experts on this subject based on the ideXlab platform.
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a new cry toxin with a unique two component dependency from Bacillus Sphaericus
The FASEB Journal, 2007Co-Authors: Gareth Wyn Jones, Zhiming Yuan, Christina Nielsenleroux, Yankun Yang, Vinicius Fiuza Dumas, Rose Gomes Monnerat, Colin BerryAbstract:Highly pathogenic strains of Bacillus Sphaericus produce the mosquitocidal Bin proteins, but resistance to this toxin can be produced under laboratory and field conditions. Analysis of strains able to overcome this resistance revealed the presence of a previously undescribed type of two-component toxin. One subunit, Cry48Aa1, is related to the 3-domain crystal toxins of Bacillus thuringiensis. Uniquely for this type of protein, insect toxicity is only achieved in the presence of a second, accessory protein, Cry49Aa1. This protein is itself related to both the binary toxin of B. Sphaericus and to Cry35 and Cry36 of B. thuringiensis, none of which require interaction with Cry48Aa1-like proteins for their activity. The necessity for both Cry48Aa1 and Cry49Aa1 components for pathogenicity, therefore, indicates an unprecedented interaction to generate toxicity. Despite high potency for purified Cry48Aa1/Cry49Aa1 proteins (LC50 for third instar Culex quinquefasciatus larvae: 15.9 ng/ml and 6.3 ng/ml respectively), bacteria producing them show suboptimal mosquitocidal activity due to low-level Cry48Aa1 production. This new toxin combination may indicate a fortuitous combination of members of the gene families that encode 3-domain Cry toxins and Binary-like toxins, permitting the "mix-and-match" evolution of a new component in the mosquitocidal armoury.--Jones, G. W., Nielsen-Leroux, C., Yang, Y., Yuan, Z., Dumas, V. F., Monnerat, R. G., Colin Berry, C. A new Cry toxin with a unique two-component dependency from Bacillus Sphaericus
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inheritance and mechanism of resistance to Bacillus Sphaericus in culex quinquefasciatus diptera culicidae from china and brazil
Journal of Medical Entomology, 2004Co-Authors: Cláudia Maria Fontes De Oliveira, Zhiming Yuan, Guofeng Pei, Christina Nielsenleroux, Mariahelena Silvafilha, Lêda RegisAbstract:Investigations on the inheritance and mechanism of resistance to Bacillus Sphaericus Neide in Culex quinquefasciatus Say colonies, selected with strains C3-41 (RLCq1/C3-41) and 2362 (CqRL1/2362), were performed in China and Brazil, respectively. The progeny of reciprocal F1 crosses (susceptible female resistant male and vice versa) from both resistant colonies responded alike in bioassays, indicating recessive inheritance. Data on larvae susceptibility from the backcross offspring between F1 and their respective susceptible and resistant parental colonies are consistent with a monofactorial and autosomal mode of inheritance. In vitro binding assays between 125 I binary (Bin2) toxin and the brush border membrane fractions (BBMF) from CqRL1/2362 and RLCq1/C3-41 larvae showed that resistance, in both colonies, is caused by a failure in the binding step of the B. Sphaericus Bin2 toxin to its speciÞc midgut receptor. The speciÞc and saturable binding of Bin2 toxin to BBMF from F1 larvae (CqRL1/2362 X susceptible counterpart) conÞrms the recessive inheritance of the resistance gene. Further studies are needed to advance understanding of B.Sphaericus resistance.
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the receptor of Bacillus Sphaericus binary toxin in culex pipiens diptera culicidae midgut molecular cloning and expression
Insect Biochemistry and Molecular Biology, 2001Co-Authors: Isabelle Darboux, Christina Nielsenleroux, Jeanfrancois Charles, David PauronAbstract:Culex pipiens larval midgut is the primary target of the binary toxin (Bin) present in parasporal inclusions of Bacillus Sphaericus. Cpm1, a 60-kDa protein purified from brush border membranes, has been proposed as the receptor of the Bin toxin in the midgut epithelial cells of mosquitoes. We have cloned and characterized the corresponding cDNA from midgut of Culex pipiens larvae. The open reading frame predicted a 580 amino-acid protein with a putative signal peptide at the N-terminus and a putative GPI-anchoring signal at the C-terminus. The amino acid sequence of the cloned Cpm1 exhibited 39-43% identities with insect maltases (alpha-glucosidases and alpha-amylases). Recombinant Cpm1 expressed in E. coli specifically bound to the Bin toxin and had a significant alpha-glucosidase activity but no alpha-amylase activity. These results support the view that Cpm1 is an alpha-glucosidase expressed in Culex midgut where it constitutes the receptor for the Bin toxin. To date, this is the first component involved in the mosquitocidal activity of the Bacillus Sphaericus Bin toxin to be characterized. Its identification provides a key step to elucidate the mode of action of the Bin toxin and the mechanisms of resistance developed against it by some mosquito strains.
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identification of the receptor for Bacillus Sphaericus crystal toxin in the brush border membrane of the mosquito culex pipiens diptera culicidae
Insect Biochemistry and Molecular Biology, 1999Co-Authors: Mariahelena Silvafilha, Christina Nielsenleroux, Jeanfrancois CharlesAbstract:The binary toxin (Bin) from Bacillus Sphaericus crystals specifically binds to soluble midgut brush border membrane proteins from Culex pipiens larvae. A single 60 kDa midgut membrane protein is identified as the binding protein. This protein is anchored in the mosquito midgut membrane via a glycosyl-phosphatidylinositol (GPI) anchor, and is partially released by phosphatidylinositol specific-phospholipase C (PI-PLC). Fractionation of soluble proteins by anion exchange chromatography indicates that the binding protein does not co-elute with leucine aminopeptidase activity. After partial purification, the sequences of internal amino acid fragments of the 60 kDa protein were determined. The peptide sequences were compared with data in GenBank, and showed a very high degree of similarity with enzymes belonging to the alpha-amylase family. Further enzymatic investigation showed that the receptor of the Bin toxin in C. pipiens larval midgut may be an alpha-glucosidase.
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resistance to Bacillus Sphaericus involves different mechanisms in culex pipiens diptera culicidae larvae
Journal of Medical Entomology, 1997Co-Authors: Christina Nielsenleroux, Jeanfrancois Charles, Florence Pasquier, Gilbert Sinegre, Bruno Gaven, Nicole PasteurAbstract:Field Culex pipiens pipiens (L.) mosquitoes that were collected after a control failure with Spherimos in southern France developed high resistance (> 10,000-fold) to Bacillus Sphaericus crystal toxin after <8 generations of laboratory selection. We show that this resistance is encoded by a single major recessive gene on linkage group I at 22.1 recombination units from the sex locus, and that it is not associated with any loss of binding affinity between brush border membrane fractions and die B. Sphaericus radiolabeled toxin. Thus, in Southern France, resistance differs from the high B. Sphaericus resistance developed after laboratory selection of Californian C. p. quinquefasciatus. This demonstrates that at least 2 different mechanisms may confer high levels of resistance to B. Sphaericus crystal toxin in mosquitoes of the C. pipiens complex. These results have important implications for mosquito control strategies.
David Pauron - One of the best experts on this subject based on the ideXlab platform.
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Bacillus Sphaericus Binary Toxin Elicits Host Cell Autophagy as a Response to Intoxication
2011Co-Authors: Nils C. Gauthier¤b, Colin Berry, Anne Doye, Pierre Gounon, Emmanuel Lemichez, David PauronAbstract:Bacillus Sphaericus strains that produce the binary toxin (Bin) are highly toxic to Culex and Anopheles mosquitoes, and have been used since the late 1980s as a biopesticide for the control of these vectors of infectious disease agents. The Bin toxin produced by these strains targets mosquito larval midgut epithelial cells where it binds to Cpm1 (Culex pipiens maltase 1) a digestive enzyme, and causes severe intracellular damage, including a dramatic cytoplasmic vacuolation. The intoxication of mammalian epithelial MDCK cells engineered to express Cpm1 mimics the cytopathologies observed in mosquito enterocytes following Bin ingestion: pore formation and vacuolation. In this study we demonstrate that Bin-induced vacuolisation is a transient phenomenon that affects autolysosomes. In addition, we show that this vacuolisation is associated with induction of autophagy in intoxicated cells. Furthermore, we report that after internalization, Bin reaches the recycling endosomes but is not localized either within the vacuolating autolysosomes or within any other degradative compartment. Our observations reveal that Bin elicits autophagy as the cell’s response to intoxication while protecting itsel
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transposon mediated resistance to Bacillus Sphaericus in a field evolved population of culex pipiens diptera culicidae
Cellular Microbiology, 2007Co-Authors: Isabelle Darboux, Jeanfrancois Charles, Yannick Pauchet, Sylvie Warot, David PauronAbstract:Summary The binary toxin is the major active component of Bacillus Sphaericus, a microbial larvicide used for controlling some vector mosquito-borne diseases. B. Sphaericus resistance has been reported in many part of the world, leading to a growing concern for the usefulness of this environmental friendly insecticide. Here we characterize a novel mechanism of resistance to the binary toxin in a natural population of the West Nile virus vector, Culex pipiens. We show that the insertion of a transposable element-like DNA into the coding sequence of the midgut toxin receptor induces a new mRNA splicing event, unmasking cryptic donor and acceptor sites located in the host gene. The creation of the new intron causes the expression of an altered membrane protein, which is incapable of interacting with the toxin, thus providing the host mosquito with an advantageous phenotype. As a large portion of insect genomes is composed of transposable elements or transposable elements-related sequences, this new mechanism may be of general importance to appreciate their significance as potent agents for insect resistance to the microbial insecticides.
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the receptor of Bacillus Sphaericus binary toxin in culex pipiens diptera culicidae midgut molecular cloning and expression
Insect Biochemistry and Molecular Biology, 2001Co-Authors: Isabelle Darboux, Christina Nielsenleroux, Jeanfrancois Charles, David PauronAbstract:Culex pipiens larval midgut is the primary target of the binary toxin (Bin) present in parasporal inclusions of Bacillus Sphaericus. Cpm1, a 60-kDa protein purified from brush border membranes, has been proposed as the receptor of the Bin toxin in the midgut epithelial cells of mosquitoes. We have cloned and characterized the corresponding cDNA from midgut of Culex pipiens larvae. The open reading frame predicted a 580 amino-acid protein with a putative signal peptide at the N-terminus and a putative GPI-anchoring signal at the C-terminus. The amino acid sequence of the cloned Cpm1 exhibited 39-43% identities with insect maltases (alpha-glucosidases and alpha-amylases). Recombinant Cpm1 expressed in E. coli specifically bound to the Bin toxin and had a significant alpha-glucosidase activity but no alpha-amylase activity. These results support the view that Cpm1 is an alpha-glucosidase expressed in Culex midgut where it constitutes the receptor for the Bin toxin. To date, this is the first component involved in the mosquitocidal activity of the Bacillus Sphaericus Bin toxin to be characterized. Its identification provides a key step to elucidate the mode of action of the Bin toxin and the mechanisms of resistance developed against it by some mosquito strains.
Zhiming Yuan - One of the best experts on this subject based on the ideXlab platform.
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Allelic Diversity and Population Structure of Bacillus Sphaericus as Revealed by Multilocus Sequence Typing
Applied and Environmental Microbiology, 2011Co-Authors: Dasheng Zheng, Zhiming YuanAbstract:The genetic diversity of 35 Bacillus Sphaericus strains was analyzed by a newly developed multilocus sequence typing (MLST) scheme, toxin gene pool survey, and mosquito bioassay. The results demonstrated that strains assigned to the same sequence type (ST) had the same occurrence of toxin genes. Further sequence analysis revealed that toxic strains presented a nearly clonal population structure, whereas nontoxic strains had a high level of heterogeneity and were significantly distinct from toxic strains.
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phylogenetic analysis and heterologous expression of surface layer protein slpc of Bacillus Sphaericus c3 41
Bioscience Biotechnology and Biochemistry, 2008Co-Authors: Bjarne Munk Hansen, Zhiming YuanAbstract:The surface layer protein encoding genes from five mosquito-pathogenic Bacillus Sphaericus isolates were amplified and sequenced. Negative staining of the S-layer protein extracted from the cell wall of wild-type B. Sphaericus C3-41 was prepared. It showed a flat-sheet crystal lattice structure. Two genes encoding the entire and N-terminally truncated S-layer protein (slpC and DeltaslpC respectively), were ligated into plasmid pET28a and expressed in Escherichia coli. SDS-PAGE revealed that about 130 KD and 110 KD proteins could be expressed in the cytoplasm of recombinant E. coli BL21(pET28a/slpC) and E. coli BL21(pET28a/DeltaslpC) respectively. Furthermore, an intracellular sheet-like or fingerprint-shape structure was investigated in two recombinant strains, which expressed SlpC and DeltaSlpC protein respectively, by ultrathin microscopy study, but bioassay results suggested that the S-layer protein of wild B. Sphaericus C3-41 and recombinant E. coli BL21 (pET28a/slpC) have no direct toxicity against mosquito larvae. These results should provide information for further understanding of the function of S-layer protein of pathogenic B. Sphaericus.
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a new cry toxin with a unique two component dependency from Bacillus Sphaericus
The FASEB Journal, 2007Co-Authors: Gareth Wyn Jones, Zhiming Yuan, Christina Nielsenleroux, Yankun Yang, Vinicius Fiuza Dumas, Rose Gomes Monnerat, Colin BerryAbstract:Highly pathogenic strains of Bacillus Sphaericus produce the mosquitocidal Bin proteins, but resistance to this toxin can be produced under laboratory and field conditions. Analysis of strains able to overcome this resistance revealed the presence of a previously undescribed type of two-component toxin. One subunit, Cry48Aa1, is related to the 3-domain crystal toxins of Bacillus thuringiensis. Uniquely for this type of protein, insect toxicity is only achieved in the presence of a second, accessory protein, Cry49Aa1. This protein is itself related to both the binary toxin of B. Sphaericus and to Cry35 and Cry36 of B. thuringiensis, none of which require interaction with Cry48Aa1-like proteins for their activity. The necessity for both Cry48Aa1 and Cry49Aa1 components for pathogenicity, therefore, indicates an unprecedented interaction to generate toxicity. Despite high potency for purified Cry48Aa1/Cry49Aa1 proteins (LC50 for third instar Culex quinquefasciatus larvae: 15.9 ng/ml and 6.3 ng/ml respectively), bacteria producing them show suboptimal mosquitocidal activity due to low-level Cry48Aa1 production. This new toxin combination may indicate a fortuitous combination of members of the gene families that encode 3-domain Cry toxins and Binary-like toxins, permitting the "mix-and-match" evolution of a new component in the mosquitocidal armoury.--Jones, G. W., Nielsen-Leroux, C., Yang, Y., Yuan, Z., Dumas, V. F., Monnerat, R. G., Colin Berry, C. A new Cry toxin with a unique two-component dependency from Bacillus Sphaericus
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molecular characterization of a glucokinase with broad hexose specificity from Bacillus Sphaericus strain c3 41
Applied and Environmental Microbiology, 2007Co-Authors: Bei Han, Dasheng Zheng, Haizhou Liu, Yajun Cai, Zhiming YuanAbstract:Bacillus Sphaericus cannot metabolize sugar since it lacks several of the enzymes necessary for glycolysis. Our results confirmed the presence of a glucokinase-encoding gene, glcK, and a phosphofructokinase-encoding gene, pfk, on the bacterial chromosome and expression of glucokinase during vegetative growth of B. Sphaericus strains. However, no phosphoglucose isomerase gene (pgi) or phosphoglucose isomerase enzyme activity was detected in these strains. Furthermore, one glcK open reading frame was cloned from B. Sphaericus strain C3-41 and then expressed in Escherichia coli. Biochemical analysis revealed that this gene encoded a protein with a molecular mass of 33 kDa and that the purified recombinant glucokinase had Km values of 0.52 and 0.31 mM for ATP and glucose, respectively. It has been proved that this ATP-dependent glucokinase can also phosphorylate fructose and mannose, and sequence alignment of the glcK gene indicated that it belongs to the ROK protein family. It is postulated that the absence of the phosphoglucose isomerase-encoding gene pgi in B. Sphaericus might be one of the reasons for the inability of this bacterium to metabolize carbohydrates. Our findings provide additional data that further elucidate the specific metabolic pathway and could be used for genetic improvement of B. Sphaericus.
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inheritance and mechanism of resistance to Bacillus Sphaericus in culex quinquefasciatus diptera culicidae from china and brazil
Journal of Medical Entomology, 2004Co-Authors: Cláudia Maria Fontes De Oliveira, Zhiming Yuan, Guofeng Pei, Christina Nielsenleroux, Mariahelena Silvafilha, Lêda RegisAbstract:Investigations on the inheritance and mechanism of resistance to Bacillus Sphaericus Neide in Culex quinquefasciatus Say colonies, selected with strains C3-41 (RLCq1/C3-41) and 2362 (CqRL1/2362), were performed in China and Brazil, respectively. The progeny of reciprocal F1 crosses (susceptible female resistant male and vice versa) from both resistant colonies responded alike in bioassays, indicating recessive inheritance. Data on larvae susceptibility from the backcross offspring between F1 and their respective susceptible and resistant parental colonies are consistent with a monofactorial and autosomal mode of inheritance. In vitro binding assays between 125 I binary (Bin2) toxin and the brush border membrane fractions (BBMF) from CqRL1/2362 and RLCq1/C3-41 larvae showed that resistance, in both colonies, is caused by a failure in the binding step of the B. Sphaericus Bin2 toxin to its speciÞc midgut receptor. The speciÞc and saturable binding of Bin2 toxin to BBMF from F1 larvae (CqRL1/2362 X susceptible counterpart) conÞrms the recessive inheritance of the resistance gene. Further studies are needed to advance understanding of B.Sphaericus resistance.
William E. Walton - One of the best experts on this subject based on the ideXlab platform.
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mtx toxins synergize Bacillus Sphaericus and cry11aa against susceptible and insecticide resistant culex quinquefasciatus larvae
Applied and Environmental Microbiology, 2007Co-Authors: Margaret C. Wirth, Brian A. Federici, William E. Walton, Yangkun Yang, Colin BerryAbstract:Two mosquitocidal toxins (Mtx) of Bacillus Sphaericus, which are produced during vegetative growth, were investigated for their potential to increase toxicity and reduce the expression of insecticide resistance through their interactions with other mosquitocidal proteins. Mtx-1 and Mtx-2 were fused with glutathione S-transferase and produced in Escherichia coli, after which lyophilized powders of these fusions were assayed against Culex quinquefasciatus larvae. Both Mtx proteins showed a high level of activity against susceptible C. quinquefasciatus mosquitoes, with 50% lethal concentrations (LC50) of Mtx-1 and Mtx-2 of 0.246 and 4.13 μg/ml, respectively. The LC50s were 0.406 to 0.430 μg/ml when Mtx-1 or Mtx-2 was mixed with B. Sphaericus, and synergy improved activity and reduced resistance levels. When the proteins were combined with a recombinant Bacillus thuringiensis strain that produces Cry11Aa, the mixtures were highly active against Cry11A-resistant larvae and resistance was also reduced. The mixture of two Mtx toxins and B. Sphaericus was 10 times more active against susceptible mosquitoes than B. Sphaericus alone, demonstrating the influence of relatively low concentrations of these toxins. These results show that, similar to Cyt toxins from B. thuringiensis subsp. israelensis, Mtx toxins can increase the toxicity of other mosquitocidal proteins and may be useful for both increasing the activity of commercial bacterial larvicides and managing potential resistance to these substances among mosquito populations.
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synergy between toxins of Bacillus thuringiensis subsp israelensis and Bacillus Sphaericus
Journal of Medical Entomology, 2004Co-Authors: Margaret C. Wirth, Brian A. Federici, Joshua A Jiannino, William E. WaltonAbstract:Synergistic interactions among the multiple endotoxins of Bacillus thuringiensis subsp. israelensis de Barjac play an important role in its high toxicity to mosquito larvae and the absence of insecticide resistance in populations treated with this bacterium. A lack of toxin complexity and synergism are the apparent causes of resistance to Bacillus Sphaericus Neide in particular Culex field populations. To identify endotoxin combinations of the two Bacillus species that might improve insecticidal activity and manage mosquito resistance to B. Sphaericus, we tested their toxins alone and in combination. Most combinations of B. Sphaericus and B. t. subsp. israelensis toxins were synergistic and enhanced toxicity relative to B. Sphaericus, particularly against Culex quinquefasciatus Say larvae resistant to B. Sphaericus and Aedes aegypti (L.), a species poorly susceptible to B. Sphaericus. Toxicity also improved against susceptible Cx. quinquefasciatus. For example, when the CytlAa toxin from B. t. subsp. israelensis was added to Bin and Cry toxins, or when native B. t. subsp. israelensis was combined with B. Sphaericus, synergism values as high as 883-fold were observed and combinations were 4-59,000-fold more active than B. Sphaericus. These data, and previous studies using cytolytic toxins, validate proposed strategies for improving bacterial larvicides by combining B. Sphaericus with B. t. subsp. israelensis or by engineering recombinant bacteria that express endotoxins from both strains. These combinations increase both endotoxin complexity and synergistic interactions and thereby enhance activity and help avoid insecticide resistance.
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Cyt1A from Bacillus thuringiensis synergizes activity of Bacillus Sphaericus against Aedes aegypti (Diptera: Culicidae)
Applied and environmental microbiology, 2000Co-Authors: Margaret C. Wirth, Brian A. Federici, William E. WaltonAbstract:Bacillus Sphaericus is a mosquitocidal bacterium recently developed as a commercial larvicide that is used worldwide to control pestiferous and vector mosquitoes. Whereas B. Sphaericus is highly active against larvae of Culex and Anopheles mosquitoes, it is virtually nontoxic to Aedes aegypti, an important vector species. In the present study, we evaluated the capacity of the cytolytic protein Cyt1A from Bacillus thuringiensis subsp. israelensis to enhance the toxicity of B. Sphaericus toward A. aegypti. Various combinations of these two materials were evaluated, and all were highly toxic. A ratio of 10:1 of B. Sphaericus to Cyt1A was 3,600-fold more toxic to A. aegypti than B. Sphaericus alone. Statistical analysis showed this high activity was due to synergism between the Cyt1A toxin and B. Sphaericus. These results suggest that Cyt1A could be useful in expanding the host range of B. Sphaericus.
