in case of Bt cotton, how does the toxic insecticide protein produced by the bacterium kills the insect pest but not the cell of Bacillus thuringiensis where the toxic protein is generated?

Explanation

Some strains of Bacillus thuringiensis produce proteins that kill certain insects as lepidopterans (tobacco budworm, armyworm). Bt forms protein crystals during a particular phase of their growth. These crys tals contain a toxic insecticidal protein. But toxin does not kill the Bacillus. Because the Bt toxin protein exists as inactive protoxins but once an insect ingests the inactive toxin, it is converted into an active form of toxin due to the alkaline pH of the gut which solubilise the crystals. The activated toxin binds to the surface of midgut epithelial cells and creates pores that cause cell swelling and lysis and eventu ally cause death of the insect.