Question

Which type of toxins are produced by Bacillus thuringiensis?

• A. \(\gamma\)-Endotoxin
• B. \(\delta\)-Endotoxin
• C. \(\alpha\)-Endotoxin
• D. \(\beta\)-Endotoxin

Hint:

The insecticidal crystal proteins (Cry and Cyt) produced by Bt are formally classified as \(\delta\)-endotoxins. They require an alkaline gut pH to be solubilized and activated.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Bacillus thuringiensis (Bt) is a Gram-positive soil bacterium known for its ability to produce parasporal crystal proteins during sporulation.
These proteins act as selective insecticidal toxins when ingested by susceptible insects.

Step 2: Detailed Explanation:
The crystalline protein inclusions produced by Bacillus thuringiensis contain protoxins known as delta-endotoxins (\(\delta\)-endotoxins).
These \(\delta\)-endotoxins are classified into two main structural protein families: Cry (crystal) and Cyt (cytolytic) toxins.
When an insect ingests these crystals, the alkaline environment of its midgut dissolves the protein crystals, and midgut proteases cleave the protoxins to release the active insecticidal toxins.
The active toxins then bind to specific receptors on the membrane of midgut epithelial cells, forming pores that disrupt osmotic balance, leading to cell lysis, gut paralysis, and insect death.
Alpha, beta, and gamma endotoxins are not the classification names used for the insecticidal crystal proteins of Bacillus thuringiensis.

Step 3: Final Answer:
Therefore, Bt produces \(\delta\)-endotoxins, corresponding to option (B).