Parasporal body

Parasporal body is a crystalline protein that forms around a spore in some bacteria that acts as a toxin precursor when digested.

For example, Bacillus thuringiensis and Bacillus sphaericus form a solid protein crystal, the parasporal body, next to their endospores during spore formation. The B. thuringiensis parasporal body contains protein toxins that kill over 100 species of moths by dissolving in the alkaline gut of caterpillars and destroying the epithelium. The solubilized toxin proteins are cleaved by midgut proteases to smaller toxic polypeptides that attack the gut epithelial cells. The alkaline gut contents escape into the blood, causing paralysis and death. One of these toxins has been shown to form pores in the plasma membrane of the target insect's cells. These channels allow monovalent cations such as potassium to pass through. B. thuringiensis toxin genes have been engineered to make a variety of pest-resistant, genetically modified plants. The B. sphaericus parasporal body contains proteins toxic for mosquito larvae and may be useful in controlling the mosquitoes that carry the malaria parasite Plasmodium.