Question

Conversion of the Bt toxin produced by Bacillus thuringiensis to its active form in the gut of the insects is mediated by

• A. Acidic pH of the gut
• B. Alkaline pH of the gut
• C. Lipid modification of the protein
• D. Cleavage by chymotrypsin

Answer 1

Answer: (B)

Alkaline pH of the gut

Bacillus thuringiensis (Bt) is a gram-positive bacterium that produces crystals during sporulation. These crystals comprise of 130 kDa protoxins called as crystal proteins which are potent and highly specific insecticides. Once ingested by the specific host, these crystals dissolve in the alkaline conditions of the gut thereby activating the protoxins. The active toxins then bind to receptors on midgut epithelial cells, become inserted into the plasma membrane where they form pores leading to cell death through osmotic lysis. Thus, option B is correct.