Question

What is true about Bt toxin?
A. The inactive protoxin gets converted into an active form in the insect cut.
B. Bt proteins exist as an active toxin in the Bacillus.
C. The activated toxin enters the ovaries of the pest to sterilize it and thus prevent its multiplication.
D. The concerned Bacillus has antitoxins.

Answer 1

Hint: The Bt toxin is an example of how microorganisms can act as biocontrol agents, functioning as a natural pesticide. It is a novel method incorporating techniques of biotechnology to agriculture.

Complete answer: Bacillus thuringiensis also known as ‘Bt’ is a gram-positive bacterium. These organisms are used as biological pesticides. A kind of gene present within Bt known as the cry gene produces the Bt protein. These protein crystals are toxic to various pests such as ball worms. These proteins exist as protoxins, that is an inactive form within the body of the bacteria. In the gut of the pest, due to certain pH of the gut, it gets converted to an active form. The activated crystals then bind to the gut of the insect. This creates a pore in the gut, thereby causing cell swelling and eventually lysis, finally leading to the death of the pest. The activated toxins act on the gut of the insect and do not act in the ovaries, and does not lead to its sterilization as well. The Bacillus does not possess antitoxins. During sporulation, many Bt strains produce crystal proteins that exhibit insecticide resistance.
Hence, the correct answer is option A.

Note: Several insects have been found to have developed resistance to toxins produced by Bt. An example of this is in the case of pink bollworm studied in certain parts of Gujarat. The subspecies B. israelensis is commonly used to control mosquitoes and of fungus gnats.