Significance of Exosporium Enclosure of Parasporal Inclusions of Bacillus thuringiensis

苏云金芽孢杆菌是一种革兰氏阳性产孢杆菌，能产生大量产孢特异性蛋白。这些蛋白质以孢子旁包涵体的形式积累，是对昆虫幼虫具有选择性活性的原毒素。通常，包裹体沉积在外孢子体外部，并与孢子分开释放到环境中。然而，在finitimus亚种中，包裹体和孢子共享共同的外孢子体，并一起释放。外孢子体比孢子更疏水性(Koshikawa等人，1989)，外孢子体包裹体比游离包裹体更疏水性。原毒素对敏感幼虫的有效性可能取决于包涵体的疏水性。以色列亚种产生由对蚊子幼虫起作用的原毒素组成的内涵体。以色列的包裹体是从孢子中分离出来的，可能是亲水性的，在自然界中这些幼虫不易获得。如果以色列的包裹体被包裹在外孢子体中，那么原毒素应该更容易获得，从而成为更有效的生防剂。初步规划研究的目的是确定外孢子体对伴生孢子包涵体疏水性的影响，并确定通过基因技术在外孢子体内工程处理以色列原毒素的可行性。%这是一项计划研究，旨在确定开发一种对蚊子幼虫有效的生物杀虫剂的可行性。这种方法是利用细菌在孢子形成过程中产生的天然抗幼虫蛋白。人和其他动物的蚊媒疾病是一个极其重大的世界性健康和经济问题，尤其是在第三世界；疟疾本身就是世界上儿童死亡的头号原因。化学杀虫剂不仅因为对动物和环境的毒性而不吸引人，而且随着昆虫对化学杀虫剂产生越来越多的抗药性，化学杀虫剂的效果越来越差。因此，开展害虫生物防治研究对人类健康和环境都具有重要意义。

Bacillus thuringiensis is a Gram-positive sporulating bacterium that produces large amounts of sporulation specific proteins. These proteins accumulate as parasporal inclusions and are protoxins with selective activity for insect larvae. Generally, the inclusion is deposited outside the exosporium and is released into the environment separately from the spore. In subspecies finitimus, however, the inclusion and the spore share the common exosporium and are released together. The exosporium is more hydrophobic than the spore (Koshikawa et al., 1989), and exosporium enclosed inclusions are expected to be more hydrophobic than free inclusions. The availability of protoxins to susceptible larvae may be dependent upon the hydrophobicity of the inclusions. Subspecies israelensis produces inclusions composed of protoxins active on mosquito larvae. The inclusions of israelensis are released separately from the spore and are probably hydrophilic and not readily available to these larvae in nature. If the inclusions of israelensis were enclosed within the exosporium, then the protoxin should be more accessible and thus a more effective biological control agent. The aims of the preliminary planning study are to determine the effects of the exosporium on the hydrophobicity of parasporal inclusions, and to determine the feasibility of engineering, by genetic techniques, the protoxin of israelensis inside an exosporium. %%% This is a planning study to determine the feasibility of developing a biological insecticide effective against mosquito larvae. The approach is to take advantage of natural antilarval proteins produced by a bacterium in the course of sporulation. Mosquito- borne diseases of man and other animals represent an extremely significant world health and economic problem, particularly in the third world; one alone, malaria, is the number one cause of childhood mortality in the world. Chemical insecticides are not only unattractive because of their toxicity to animals and the environment, but they are becoming less and less effective as insects increasingly develop resistance to them. This research on biological pest control is therefore of great significance to both human health and the environment.