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The Preparation Of Microcapsules Of Bacillus Thuringiensis Parasporal Crystal

Posted on:2017-03-28Degree:MasterType:Thesis
Country:ChinaCandidate:X L HeFull Text:PDF
GTID:2283330503458662Subject:Biology
Abstract/Summary:PDF Full Text Request
Parasporal crystals which have insecticidal activity could be synthesized by Bacillus thuringiensis(Bt). Bt has been widely used as environmentally friendly microbial pesticides because of their toxicity for specific insects in their larval phase and innocuity for vertebrates and plants. Therefore, Bt has been widely available in crop protection field and regarded as the main bioinsecticide. However, parasporal crystals are easy to be influenced by different environmental stresses, such as high temperature, ultraviolet radiation, and desiccation. To enhance the resistance of parasporal crystals to environment and extend their activity, various Bt formulations have been developed. Under this background, this paper pays attention to develope a new type of formulation:microcapsules of crystals.The microcapsules were self-assembled by the alternate deposition of low-cost bio-polymer materials, such as chitosan, sodium alginate and sodium carboxymethyl cellulose, on the surface of Cry8Ca2 spherical crystals or Cry1 Ac rhomboid crystals layer-by-layer. SEM images were shown that the size of Cry8Ca2 crystal microcapsules were about 0.6 ? 0.8 μm and Cry1 Ac crystal microcapsules were about 0.6 ? 1.2 μm,which were all suitable for spraying and larvae feeding. Cry1 Ac crystal microcapsules could release inside crystals above pH 9.0 and were stable at pH 6.0 in water, which enhanced the storage period. While, the release of the encapsulated Cry8Ca2 crystals was triggered at pH 10.2, which indicated that different inside crystals resulted in different releasing pH of microcapsules.Insecticidal activity assays demonstrated that Cry1 Ac crystal microcapsules had statistically equivalent toxicity to free crystals mixed with spores. And bio-polymer materials, which were utilized in microcapsules preparation, were none of toxicity to larvae. At the same time, resistance to environmental stresses indicated that Cry1 Ac crystal microcapsules could protect crystals in several environmental stresses, such as high temperature, UV radiation and desiccation, increasing the stability of insecticidal activity of crystals.In this research, directly using parasporal crystals as template could reduce preparation costs of microcapsules. Meanwhile, bio-polymer materials for microcapsules preparation were all biocompatibility and biodegradability. This is a new method for crystal protein protection, providing a new strategy for the stability of Bt application and establishing a good experimental foundation.
Keywords/Search Tags:Bacillus thuringiensis, microcapsule, Cry8Ca2 crystal, Cry1Ac crystal
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