Question

The inactive form of Bt toxin is converted to the active form in the insect gut

• A. by nucleases
• B. due to alkaline pH
• C. due to acidic pH
• D. by proteases

Hint:

• Bt toxin does not affect mammals (including humans) because the mammalian stomach is highly acidic, preventing the solubilization and activation of the protoxin crystals.

• Transgenic plants (such as Bt Cotton and Bt Brinjal) express these bacterial cry genes to provide targeted resistance against specific pests without chemical pesticides.

Answer 1

The Correct Option is B

Step 1: Recall what Bt toxin is.
Bacillus thuringiensis makes insecticidal crystal (Cry) proteins during sporulation. These are produced as inactive protoxins so they do not harm the bacterium itself.
Step 2: Note where activation happens.
The protoxin only becomes active after an insect eats it and it reaches the insect midgut.
Step 3: Recall the gut environment.
The midgut of target insects has a highly alkaline pH, very different from the bacterium's own conditions.
Step 4: Trace the activation.
The alkaline pH dissolves the crystal protein, turning the insoluble crystal into a soluble form. This solubilisation is the key step.
Step 5: Compare with the options.
Nucleases and acidic pH play no role here. Proteases do help cleave the protein, but the primary requirement that converts the inactive crystal is the solubilisation driven by the alkaline pH.
Step 6: Conclude.
So the inactive Bt toxin is converted to the active form mainly due to the alkaline pH of the insect gut.
\[ \boxed{\text{due to alkaline pH}} \]