• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 134
  • 50
  • 23
  • 10
  • 9
  • 4
  • 3
  • 2
  • 1
  • Tagged with
  • 253
  • 253
  • 60
  • 42
  • 36
  • 34
  • 27
  • 25
  • 21
  • 20
  • 19
  • 19
  • 17
  • 16
  • 14
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Isolation and Characterization of Bacillus Thuringiensis Strains From Different Grain Habitats/

Apaydın, Özgür. Güneş, Hatice January 2004 (has links) (PDF)
Thesis (Master)--İzmir Institute of Technology, İzmir, 2004. / Includes bibliographical references (leaves.46-58).
2

Interação das toxinas Cry do Bacillus thuringiensis svar. israelensis com o mesêntero de larvas do vetor Aedes aegypti (Diptera: Culicidae) / Interaction of Cry toxins from Bacillus thuringiensis svar. israelensis with the mesenteron of the larvae of the vector Aedes aegypti (Diptera: Culicidae)

Beltrão, Henrique de Barros Moreira January 2006 (has links)
Made available in DSpace on 2012-05-07T14:43:55Z (GMT). No. of bitstreams: 2 license.txt: 1748 bytes, checksum: 8a4605be74aa9ea9d79846c1fba20a33 (MD5) 000004.pdf: 691391 bytes, checksum: c2676ae4df935413ee508028e9a02a22 (MD5) Previous issue date: 2006 / O Bacillus thuringiensis svar. israelensis (Bti) é um importante entomopatógeno utilizado na produção de larvicidas para o controle do Aedes aegypti, vetor da dengue. A toxicidade do Bti está baseada no cristal, produzido durante a esporulação, que contém quatro protoxinas Cry11Aa (70 kDa), Cry4Aa (125 kDa), Cry4Ba (130 kDa) e Cyt1A (28 kDa). Sua ação ocorre através da ingestão dos cristais que são solubilizados no mesêntero, onde as protoxinas são liberadas e clivadas por serina-proteases em toxinas ativas que agem em sinergia no epitélio intestinal e provocam a morte das larvas. Apesar da alta seletividade do Bti, ainda não foi completamente elucidado como as toxinas Cry interagem com os receptores específicos presentes no epitélio das larvas. O objetivo principal do trabalho foi caracterizar, através de ensaios in vitro de natureza quantitativa, a capacidade de ligação de cada toxina Cry (4Aa, 4Ba e 11Aa) às preparações de microvilli intestinal (BBMF) de larvas de Ae. aegypti. Para tal, cada componente Cry foi produzido a partir de cepas recombinantes, Bt cepa 4Q2-81, para produção de biomassas. A atividade inseticida das biomassas para larvas do 3o/4o estádios foi determinada através de bioensaios e, outra parte da biomassa foi utilizada para a obtenção dos cristais. Os cristais contendo cada protoxina foram processados in vitro e uma amostra de cada uma delas foi marcada com iodo (I125). Para realizar os estudos de ligação foram feitas preparações BBMF, a partir de larvas do 3o/4o estádios. Os estudos da capacidade de ligação da toxina foram realizados através de ensaios de competição, de saturação e de cinética, através de incubações entre a toxina- I125 e preparações de BBMF, na ausência ou na presença de um competidor. (...) Os resultados obtidos mostraram que as toxinas Cry competem pelos mesmos sítios e partilham receptores presentes na BBMF. Em todos os casos estudados, a afinidade do complexo toxinareceptor não foi elevada, e não foi detectada sinergia entre as toxinas Cry para a ligação à BBMF. A ligação entre as toxinas-I125 e a BBMF é irreversível, e observou-se uma forte tendência à oligomerização nos três casos. Os resultados obtidos nesse trabalho sugerem que a toxicidade das toxinas Cry para larvas de Aedes está relacionada à etapa irreversível de ligação com os receptores, e não é caracterizada por um padrão elevado de afinidade do complexo toxina-receptor ...
3

Resistance against endotoxin from Bacillus thuringiensis in Lepidopteran insects / Muhammad Sarjan.

Sarjan, Muhammad January 2002 (has links)
"December 2002" / Bibliography: leaves 99-118. / ix, 118 leaves : ill. (some col.), plates (some col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / The major aim of this study was to investigate the possible molecular mechanism of resistance against Bt-toxin based on observations that Bt-toxin binds to a soluble immune-defence component. The binding of Bt-toxin to glycosylated lipophorin in the gut was found to be consistent with a model where the toxin is inserted into the membrane by an endocytosis mechanism. In resistant insects, the primary Bt-target is an immune-complex in the gut lumen and at the peritrophic membrane, which inactivates the toxin by a coagulation process. / Thesis (Ph.D.)--University of Adelaide, Dept. of Applied and Molecular Ecology, 2003
4

Inducible tolerance to Bacillus thuringiensis (Bt) endotoxins based on cell-free immune reactions.

Rahman, Mohammad Mahbubur January 2006 (has links)
Title page, table of contents and abstract only. The complete thesis in print form is available from the University of Adelaide Library. / The use of Bacillus thuringiensis (Bt) endotoxins to control insect vectors of human diseases and agricultural pests is threatened by the possible evolution of resistance in major pest species. Despite the use of Bt-endotoxins in transgenic crops covering about 80 million hectares, the precise details of how endotoxins bind to gut cells to kill insects are poorly understood. This limitation impedes our understanding of potential mechanisms of insect resistance to Bt-endotoxins other than the loss or modification of receptors. We explored a novel mechanism, where tolerance to Bt-endotoxins is correlated with an elevated immune status involving cell-free immune reactions in the gut lumen. The thesis project is based on investigations of a laboratory culture of the flour moth Ephestia kuehniella, which showed induction of hemolymph melanization a sign of immune induction, after feeding sub-lethal concentrations of a Bt-formulation. Since the elevated immune status was transmitted to subsequent generations by a maternal effect, an increase of toxin in the food by increments was possible every generation. Investigations of strains exposed to various toxin levels revealed a correlation between systemic immune induction and Bt-tolerance. Molecular analysis revealed a possible mechanism of immune mediated inactivation of Bt-endotoxins in the gut lumen. To gain more specific information about the effector pathways involved in the protection against the toxin, we studied the effects of Bt-toxin formulations in susceptible (non-induced) and tolerant (immune-induced) larvae after natural (parasitism-mediated) and chemical (tropolone-mediated) suppression of defence reactions. Although melanization in hemolymph was significantly reduced, there was no significant effect on susceptibility to the toxin in parasitised or tropolone-treated larvae. This suggests that melanization of hemolymph is correlated with an elevated immune status but not responsible for the observed tolerance to Bt-toxin. This leaves coagulation as a likely mechanism for Bt-tolerance in the gut lumen. To examine whether hemolymph proteins exist in the gut lumen were they could function as pro-coagulants to inactivate the toxin; we compared gut and plasma proteins of immune-induced larvae with those of non-induced larvae. This analysis revealed that the lipid carrier lipophorin represents a major component in the gut lumen and interacts with mature Bt-toxin like an oligomeric lectin that may inactivate the toxin in a cell free coagulation reaction in the gut lumen before it can reach the brush border membrane. Further analysis showed that lipophorin particles are the regulatory and effector components in innate immune defence reactions, which are involved in the recognition and inactivation of lipopolysaccharides (LPS) and bacteria even in the absence of hemocytes. Examination of proteins from lipophorin particles separated by low-density gradient centrifugation have shown that in immuneinduced insects sub-populations of lipophorin particles are associated with pattern recognition proteins, phenoloxidase and regulatory proteins that activate prophenoloxidase. Moreover, interactions with lectins resulted in the assembly of lipophorin particles into cage-like coagulation products, effectively protecting the surrounding tissues and cells from the potentially damaging effects of pathogens and phenoloxidase products. This cell-free immune reaction mediated by lipophorin particles may potentially involve in detoxification of poreforming toxins (Bt-endotoxins) in the gut lumen. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1259896 / Thesis (Ph.D.) -- University of Adelaide, School of Agriculture, Food and Wine, 2006
5

Inducible tolerance to Bacillus thuringiensis (Bt) endotoxins based on cell-free immune reactions.

Rahman, Mohammad Mahbubur January 2006 (has links)
Title page, table of contents and abstract only. The complete thesis in print form is available from the University of Adelaide Library. / The use of Bacillus thuringiensis (Bt) endotoxins to control insect vectors of human diseases and agricultural pests is threatened by the possible evolution of resistance in major pest species. Despite the use of Bt-endotoxins in transgenic crops covering about 80 million hectares, the precise details of how endotoxins bind to gut cells to kill insects are poorly understood. This limitation impedes our understanding of potential mechanisms of insect resistance to Bt-endotoxins other than the loss or modification of receptors. We explored a novel mechanism, where tolerance to Bt-endotoxins is correlated with an elevated immune status involving cell-free immune reactions in the gut lumen. The thesis project is based on investigations of a laboratory culture of the flour moth Ephestia kuehniella, which showed induction of hemolymph melanization a sign of immune induction, after feeding sub-lethal concentrations of a Bt-formulation. Since the elevated immune status was transmitted to subsequent generations by a maternal effect, an increase of toxin in the food by increments was possible every generation. Investigations of strains exposed to various toxin levels revealed a correlation between systemic immune induction and Bt-tolerance. Molecular analysis revealed a possible mechanism of immune mediated inactivation of Bt-endotoxins in the gut lumen. To gain more specific information about the effector pathways involved in the protection against the toxin, we studied the effects of Bt-toxin formulations in susceptible (non-induced) and tolerant (immune-induced) larvae after natural (parasitism-mediated) and chemical (tropolone-mediated) suppression of defence reactions. Although melanization in hemolymph was significantly reduced, there was no significant effect on susceptibility to the toxin in parasitised or tropolone-treated larvae. This suggests that melanization of hemolymph is correlated with an elevated immune status but not responsible for the observed tolerance to Bt-toxin. This leaves coagulation as a likely mechanism for Bt-tolerance in the gut lumen. To examine whether hemolymph proteins exist in the gut lumen were they could function as pro-coagulants to inactivate the toxin; we compared gut and plasma proteins of immune-induced larvae with those of non-induced larvae. This analysis revealed that the lipid carrier lipophorin represents a major component in the gut lumen and interacts with mature Bt-toxin like an oligomeric lectin that may inactivate the toxin in a cell free coagulation reaction in the gut lumen before it can reach the brush border membrane. Further analysis showed that lipophorin particles are the regulatory and effector components in innate immune defence reactions, which are involved in the recognition and inactivation of lipopolysaccharides (LPS) and bacteria even in the absence of hemocytes. Examination of proteins from lipophorin particles separated by low-density gradient centrifugation have shown that in immuneinduced insects sub-populations of lipophorin particles are associated with pattern recognition proteins, phenoloxidase and regulatory proteins that activate prophenoloxidase. Moreover, interactions with lectins resulted in the assembly of lipophorin particles into cage-like coagulation products, effectively protecting the surrounding tissues and cells from the potentially damaging effects of pathogens and phenoloxidase products. This cell-free immune reaction mediated by lipophorin particles may potentially involve in detoxification of poreforming toxins (Bt-endotoxins) in the gut lumen. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1259896 / Thesis (Ph.D.) -- University of Adelaide, School of Agriculture, Food and Wine, 2006
6

Saprophagous caterpillars (Lepidoptera: Noctuidae: Herminiinae) effect of Bacillus thuringiensis var. kurstaki application in forest and laboratory settings /

Kish, Karen Jeanine, January 2004 (has links)
Thesis (M.S.)--West Virginia University, 2004. / Title from document title page. Document formatted into pages; contains viii, 40 p. : ill. (some col.), map. Vita. Includes abstract. Includes bibliographical references (p. 36-39).
7

Diversity, abundance, and the effect of Bacillus thuringiensis var. kurstaki Berliner and Gypchek on larval and adult Symphyta in Virginia and West Virginia

Braud, Rachel Ann. January 2001 (has links)
Thesis (M.S.)--West Virginia University, 2001. / Title from document title page. Document formatted into pages; contains x, 87 p. : ill. (some col.), map. Vita. Includes abstract. Includes bibliographical references (p. 76-82).
8

Population dynamics of selected Lepidoptera associated with gypsy moth [Lymantria dispar (L.)] in central Appalachia

Raimondo, Sandra. January 1900 (has links)
Thesis (Ph. D.)--West Virginia University, 2003. / Title from document title page. Document formatted into pages; contains xi, 159 p. : ill., maps. Vita. Includes abstract. Includes bibliographical references.
9

Aktivierung und Inaktivierung des Cry8C-Toxins von Bacillus thuringiensis japonensis Stamm Buibui im Darmsystem von Engerlingen (Scarabaeidae)

Wagner, Wolfgang. January 1900 (has links) (PDF)
Heidelberg, Universiẗat, Diss., 2002.
10

Isolation and characterization of Bacillus thuringiensis from olive tree-related habitats/

Çınar, Çelenk. Güneş, Hatice January 2005 (has links) (PDF)
Thesis (Master)--İzmir Institute of Technology, İzmir, 2005. / Keywords:Isolation, characterisation, Bacillus thuringiensis, crystal gene, biopesticide.

Page generated in 0.1149 seconds