Question

At what pH insecticidal protein synthesized by Bacillus thuringiensis becomes active?

• A. Acidic pH
• B. Alkaline pH
• C. Neutral pH
• D. First acidic then alkaline pH

Hint:

Bt toxin is widely used in genetically modified crops like Bt cotton to resist insect pests.

Answer 1

The Correct Option is B

Step 1: Understanding Bt toxin.
Bacillus thuringiensis (Bt) produces insecticidal proteins known as Cry proteins. These proteins act as biopesticides against insect pests.
Step 2: Mechanism of action.
When ingested by insect larvae, the Cry protein crystals dissolve in the insect midgut, which has an alkaline pH. The protein is then activated and binds to the gut epithelial cells, causing lysis and ultimately the death of the insect.
Step 3: Analyzing options.
(A) Acidic pH: Incorrect — The crystals do not activate in acidic conditions.
(B) Alkaline pH: Correct — Activation of Cry proteins occurs in the alkaline medium of insect midgut.
(C) Neutral pH: Incorrect — The activation requires alkalinity.
(D) First acidic then alkaline pH: Incorrect — Only alkaline pH is essential.
Step 4: Conclusion.
Bt insecticidal protein becomes active at an alkaline pH.