MCQ
Bacillus thuringiensis forms protein crystals which contain insectidical protein. This protein
  • binds with epithelial cells of midgut of the insect pest ultimately killing it.
  • B
    is coded by several genes including the gene cry.
  • C
    is activated by acid $pH$ of the foregut of the insect pest.
  • D
    does not kill the carrier bacterium which is itself resistant to this toxin.

Answer

Correct option: A.
binds with epithelial cells of midgut of the insect pest ultimately killing it.
a
(a) : Soil bacterium Bacillus thuringiensis produces proteins that kill certain insects like lepidopterans (tobacco budworm, armyworm), coleopterans (beetles) and dipterans (flies, mosquitoes). B.thuringiensis forms some protein crystals. These crystals contain a toxic insecticidal protein. This toxin does not kill the Bacillus (bacterium) because it exists as inactive protoxins in them. But, once an insect ingests it, it is converted into an active form of toxin due to the alkaline $pH$ of the alimentary canal. The activated toxin binds to the surface of midgut epithelial cells and create pores that cause swelling and lysis and finally cause death of the insect.

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