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的产孢细菌，可产生大量的产孢特异性蛋白。这些蛋白质以副孢子包涵体的形式积累，是对昆虫幼虫具有选择性活性的原毒素。一般来说，包裹体沉积在外孢子外，并与孢子分开释放到环境中。然而，在亚种有限孢子中，包涵体和孢子共享一个外孢子，并一起释放。外孢子囊比孢子更疏水（Koshikawa et al., 1989），外孢子囊封闭的内含物预计比自由内含物更疏水。原毒素对易感幼虫的有效性可能取决于包裹体的疏水性。亚种以色列蚊产生由原毒素组成的包体，对蚊子幼虫有活性。以色列虫的内含物与孢子分开释放，可能是亲水性的，在自然界中这些幼虫不容易得到。如果以色列人的包涵体被封闭在外孢子中，那么原毒素应该更容易接近，因此是一种更有效的生物防治剂。初步规划研究的目的是确定外孢子对副孢子包涵体疏水性的影响，并确定通过基因技术在外孢子内工程化以色列人原蛋白的可行性。%%%这是一项计划研究，以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产孢过程中产生的天然抗幼虫蛋白。人类和其他动物的蚊媒疾病是一个极其重大的世界卫生和经济问题，特别是在第三世界；其中之一，疟疾，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没有吸引力，而且由于昆虫对它们越来越产生抗药性，它们的效果也越来越差。因此，害虫生物防治的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.