NCERT · Class 12 · Biology · Biotechnology and its ApplicationsExplain the role of Bacillus thuringiensis in producing insect-resistant cotton plants. How do the insecticidal proteins work inside the insect body?

Bacillus thuringiensis is a soil bacterium that produces crystal proteins during a particular phase of their growth. These protein crystals contain a toxic insecticidal protein (Bt toxin). Interestingly, the Bt toxin protein itself does not kill the bacterium because it exists as inactive protoxins in the bacterium. \nHowever, once an insect ingests the inactive protoxin, it is converted into an active form of toxin due to the alkaline pH of the gut, which solubilizes the crystals. The activated toxin binds to the surface of midgut epithelial cells and creates pores that cause cell swelling and lysis, eventually leading to the death of the insect. \nScientists have isolated specific Bt toxin genes from Bacillus thuringiensis and incorporated them into several crop plants such as cotton. Proteins encoded by the genes cryIAb and cryIIAb control cotton bollworms, and cryIAc controls corn borer. When pests feed on these transgenic plants (like Bt cotton), the ingested toxin kills them, thereby protecting the crops naturally without requiring external chemical pesticides.