Read the following statements about Bt toxin:
I. The Bt toxin gene is obtained from the bacterium Bacillus thuringiensis.
II. Bt toxin protein exists in the bacterium as an inactive protoxin.
III. The protoxin is converted into the active toxin by the acidic pH of the insect gut.
IV. The active toxin binds to the surface of midgut epithelial cells and creates pores.
Choose the correct option.
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → I, II and IV
True. I. The Bt toxin gene is obtained from the bacterium Bacillus thuringiensis. “Bt” stands for this bacterium. Its toxin gene has been cloned and expressed in plants such as Bt cotton.
True. II. Bt toxin protein exists in the bacterium as an inactive protoxin. The toxin is stored in crystals in an inactive form, which is why it does not kill the bacterium itself.
False. III. The protoxin is converted into the active toxin by the acidic pH of the insect gut. The insect gut is alkaline, not acidic. The alkaline pH dissolves the crystals and activates the toxin.
True. IV. The active toxin binds to the surface of midgut epithelial cells and creates pores. The pores make the cells swell and burst, and the insect dies.
Statements I, II and IV are correct.
NCERT Extract:
Biotechnological Applications in Agriculture – “… Bt toxin is produced by a bacterium called Bacillus thuringiensis (Bt for short). … Actually, the Bt toxin protein exist as inactive protoxins but once an insect ingest 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 create pores that cause cell swelling and lysis and eventually cause death of the insect.”