Question

Crystals of Bt toxin produced by some bacteria do not kill the bacteria themselves because

• A. Bacteria encloses toxin in a special sac
• B. Toxin is immature
• C. Toxin is inactive
• D. Bacteria are resistant to the toxin

Answer 1

The correct option is C Toxin is inactive

Bt toxin is the most popular bio-pesticide. It is a crystal protein having insecticidal properties produced by the bacterium, Bacillus thuringiensis.

Bacillus thuringiensis, during sporulation, forms crystalline proteins that have insecticidal properties. These are called the delta endotoxins (cry proteins). The endotoxin that accumulates in bacteria is in an inactive form (protoxin).

It gets activated at an alkaline pH in the midgut of the insects due to the solubilisation of the crystal proteins. This active toxin generates pores in the epithelium of the midgut of the insects which results in the swelling of cells followed by lysis. The insect consequently dies.

Bacillus thuringiensis produces a crystal protein which is a protoxin and remains inactive at acidic pH. It is an insecticidal toxin. Thus, it does not have any effect on bacteria.

Hence the correct option is
a. Toxin is inactive