Question

Study the following statements regarding Bt toxins produced by bacterium Bacillus thuringiensis and select the correct one.

• A. Most strains of Bacillus thuringiensis produce proteins that kill certain insects such as lepidopterans, cqleopterans and dipterans
• B. Bt toxin proteins do not kill the bacteria themselves because the toxin proteins occur in an inactive form called protoxins
• C. When an insect ingests the inactive Bt toxin, it is converted to an active form of toxin due to alkaline $pH$ of the gut which solubilises the protein toxin crystals
• D. All of these

Answer 1

Answer: (D)

Soil bacterium, Bacillus thuringiensis (Bt) produces proteins that kill certain insects like lepidopterans (tobacco budworm, armyworm), coleopterans (beetles) and dipterans (flies, mosquitoes). Bacillus thuringiensis forms some intracellular protein crystals. These crystals contain a toxic insecticidal protein. The Bt toxin protein exists as inactive toxin and is converted into an active form due to the alkaline $pH$ of the alimentary canal that solubilises the crystals. The activated toxin binds to the surface of midgut epithelial cells and create pores which cause cell swelling and lysis and finally cause death of the insect.