Question

When Bacillus thuringiensis enters a certain insect’s body, the insect gets killed, but itself remains unaffected. Explain how it is possible. [3 marks]

Answer 1

Bacillus thuringiensis produce protein crystals during a particular phase of their growth that kill certain insects such as lepidopterans (tobacco budworm, armyworm),
coleopterans (beetles) and dipterans (flies, mosquitoes). These crystals contain a toxic insecticidal protein which exists 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. [3 marks]