Question

Given below are two statements
Statement I: Bacillus thuringiensis acts as stomach poison in insects
Statement II: Bacillus thuringiensis is a non-crystalliferous entomopathogenic bacteria
In light of the above statements, choose the most appropriate answer from the options given below

• A. Both Statement I and Statement II are correct
• B. Both Statement I and Statement II are incorrect
• C. Statement I is correct but Statement II is incorrect
• D. Statement I is incorrect but Statement II is correct

Hint:

Bt is a crystalliferous bacterium that produces parasporal crystals (delta-endotoxins). These crystals act specifically as a stomach poison upon ingestion by susceptible insects.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Bacillus thuringiensis (Bt) is a soil-dwelling, spore-forming bacterium widely used as a biological pesticide.
Bt is highly specific and targets insects in orders like Lepidoptera, Diptera, and Coleoptera.
Its insecticidal activity is determined by specific crystalline proteins produced during sporulation.

Step 2: Detailed Explanation:
Let us analyze each statement individually:
1. Statement I describes the mode of action of Bt.
During sporulation, Bt produces parasporal crystalline inclusions called delta-endotoxins.
When an insect ingests these crystals, they are dissolved in the highly alkaline environment of the insect's midgut.
The dissolved toxins are cleaved by midgut proteases into active, smaller toxins that bind to specific receptors on the midgut epithelial cells.
This binding forms pores in the cell membrane, leading to osmotic lysis, gut paralysis, and starvation or septicemia.
Because the toxin must be ingested to be effective and acts specifically on the digestive tract, it is classified as a stomach poison.
Thus, Statement I is correct.
2. Statement II describes the biological nature of Bt.
Because Bt produces distinct parasporal crystalline inclusions (Cry and Cyt proteins), it is classified as a crystalliferous bacterium.
These crystals are the primary source of its insecticidal properties.
Stating that Bt is "non-crystalliferous" is incorrect.
Thus, Statement II is incorrect.
Therefore, Statement I is correct, and Statement II is incorrect.

Step 3: Final Answer
Statement I is correct, but Statement II is incorrect.