Question

Bacillus thuringiensis forms protein crystals that contain an insecticidal protein which
A. Binds with epithelial cells of the midgut of the insect pest ultimately killing it
B. Does not kill the carrier bacterium which is itself resistant to this toxin
C. Is activated by the acid pH of the foregut of the insect pest
D. None of these

Answer 1

Hint: Bacillus thuringiensis is a type of bacteria. It forms the endotoxin protein. This protein is insect resistant. It is used to develop insect-resistant varieties of plants. Endotoxin kills the insects by damaging portions of their alimentary canal.

Complete step by step answer: Insects can eat both plants and bacteria. Due to this reason, several bacteria have evolved specialized mechanisms to save themselves from insect prey. One such bacteria is Bacillus thuringiensis. Bacillus thuringiensis forms the intracellular crystalline bodies during sporulation. These intracellular crystalline bodies contain an insecticidal protein called endotoxin. The endotoxin that gets accumulated in the bacteria is actually an inactive precursor. When the insect ingests this bacterium then the endotoxin is cleaved by the protease enzyme. This is due to the alkaline conditions of the gut of the insect. It causes the formation of the shorter versions of the protoxin, all of which show a highly toxic activity. These proteins bind with the inside of the midgut of the insects and then damage the surface epithelium by creating pores that cause swelling and lysis. Due to this reason, the insect is unable to eat and feed continuously and it starves to death. Thus, the endotoxin is also known as the Bt toxin. Therefore, based on the above information we can conclude that Bacillus thuringiensis forms protein crystals that contain an insecticidal protein that binds with epithelial cells of the midgut of the insect pest ultimately killing it.
Hence, the correct answer is option (A).

Note: Bt toxin has been cloned in the bacteria and it is used in the plants to provide natural resistance against insects. This effort created the Bio-pesticides successfully. Specific Bt toxin genes are isolated from the Bacillus thuringiensis bacteria and then incorporated in the crop plants. The choice of a gene depends on the crop and the pest.