What do the protein crystals produced by Bacillus thuringiensis contain?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Toxic insecticidal protein
Some strains of the bacterium Bacillus thuringiensis (Bt) kill certain insects such as lepidopterans, beetles and flies. At one phase of growth the bacterium forms protein crystals. These crystals hold the Bt toxin, in an inactive form called a protoxin.
Option (1) Toxic insecticidal protein — Correct. The crystals contain a toxic insecticidal protein. When an insect eats it, the alkaline pH of the insect’s gut dissolves the crystals and activates the toxin. The active toxin makes pores in the gut cells, and the insect dies.
Option (2) Non-toxic insecticidal protein — Incorrect. The protein is inactive inside the crystal, but it is not non-toxic. It becomes active in the insect gut and kills the insect.
Option (3) Simple protein — Incorrect. The crystals do not hold just any simple protein. They hold a specific toxin coded by the cry genes that kills insects.
Option (4) Simple lipids — Incorrect. Lipids are fats. The crystals are made of protein, not lipid.
NCERT Extract:
Bt Cotton – “Some strains of Bacillus thuringiensis produce proteins that kill certain insects such as lepidopterans (tobacco budworm, armyworm), coleopterans (beetles) and dipterans (flies, mosquitoes). B. thuringiensis forms protein crystals during a particular phase of their growth. These crystals contain a toxic insecticidal protein. … 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.”