Question

Cyt toxins belong to a class of toxins known as

• A. Spore forming toxins
• B. Gut infecting toxins
• C. Pore forming toxins
• D. Wart forming toxins

Hint:

Both Cry and Cyt toxins from Bt destroy the midgut cell membrane of insects by creating microscopic holes. Thus, they are textbook examples of "Pore-forming toxins" (PFTs).

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Bacillus thuringiensis (Bt) produces insecticidal proteins during sporulation.
These proteins are categorized into two primary structural groups: Crystal (Cry) toxins and Cytolytic (Cyt) toxins.
Both groups are highly effective biopesticides but possess different mechanisms of action.

Step 2: Detailed Explanation:
Cyt toxins are specialized cytolytic proteins produced primarily by mosquitocidal strains of Bt, such as Bacillus thuringiensis israelensis.
Unlike Cry toxins, which bind to specific glycoprotein receptors on midgut epithelial cells, Cyt toxins exhibit a broader, lipid-mediated action.
Once ingested by a susceptible insect host, the alkaline environment of the midgut solubilizes the protoxin.
Midgut proteases then cleave the protoxin to activate the toxic core.
The activated Cyt toxins bind directly to the phospholipid membrane of the epithelial cells.
They aggregate and insert themselves into the host cell membrane, forming transmembrane channels.
This represents a classic mechanism of pore-forming toxins (PFTs).
The formation of these pores destroys the osmotic balance of the gut cells, leading to influx of water, cell swelling, colloid-osmotic lysis, and ultimately death of the insect.
Therefore, Cyt toxins are categorized biologically as pore-forming toxins.

Step 3: Final Answer:
Cyt toxins are membrane-disrupting proteins that belong to the pore-forming toxin class.
Thus, the correct option is (C).