Question

Bacillus thuringiensis forms protein crystals that contain an insecticidal protein which

• A. Binds with epithelial cells of mid-gut 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 acid pH of the foregut of the insect pest.
• D. None of these

Answer 1

Answer: (A)

Binds with epithelial cells of mid-gut of the insect pest ultimately killing it

Upon sporulation, B. thuringiensis forms crystals of proteinaceous insecticidal -endotoxins (called crystal proteins or Cry proteins), which are encoded by several cry genes. When insects ingest toxin crystals, do not kill the insect as it is in the inactive form. This toxin is converted into the activated form due to the alkaline pH of the gut that insolubilizes the crystal. The Cry toxin is then inserted into the insect midgut epithelial cell membrane, paralyzing the digestive tract and forming a pore. The insect stops eating and starve to death; live Bt bacteria may also colonize the insect which can contribute to death.

So, the correct answer is both 'Binds with epithelial cells of the midgut of the insect pest ultimately killing it'.