Question

Why does BT toxin does not kill the bacterium that produces it, but kill the insect that ingests it?

Answer 1

Bt toxin is produced by bacteria Bacillus thuriengiensis. During sporulation, these bacteria forms intracellular crystalline bodies that contain an insecticidal protein called the endotoxin. Bt toxin does not kill the bacterium that produces it, but kill the insect that ingests it because the endotoxin that accumulates in the bacterium is an inactive precursor. It gets activated only in the alkaline gut of insect. When insect ingests it, then protoxin is cleaved by proteases (alkaline conditions in gut), resulting is shorter versions of the protein that display the toxic activity, by binding to the inside of the insects mid gut and damages the surface epithelium by creating pores that cause swelling and lysis. So, that insect is unable to feed and consequently starves to death.