Question

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

A. Bacteria are resistant to the toxin  

B. Toxin is immature 

C. Toxin is inactive

D. Bacteria enclose toxin in a special sac

Answer 1

Hint: An important application of biotechnology is in agriculture for the production of pest-resistant plants which could decrease the number of pesticides used. These types of plants are known as hybrid plants. 

Complete answer:

As we know, BT toxin is produced by a bacterium called Bacillus thuringiensis, BT in BT toxin stands for Bacillus thuringiensis. The toxin gene has been cloned from bacteria and has been expressed in plants to provide resistance to insects without the need for insecticides. Examples are BT cotton, BT corn, tomato, potato, and soybean, etc. Some strains of Bacillus thuringiensis produce proteins that kill certain insects such as lepidopterans (tobacco budworm, armyworm), coleopterans (beetles), and dipterans (flies, mosquitoes). B. thuringiensis forms protein crystals during a particular phase of their growth. This crystal during a particular phase of their growth contains a toxic insecticidal protein. But why does this toxin kill the Bacillus? 

The Bt toxin protein exists as latent protoxins in the bacillus. So the Bacillus is not killed. However, once a bug ingests the inert toxin, it is covered into a functioning type of poison because of the soluble PH of the insect gut which solubilizes the toxin stones. In 1911 Ernst Berliner isolated a bacteria that had killed a Mediterranean flour moth in 1911, and rediscovered this toxin. He named it Bacillus thuringiensis, after the German town ‘Thuringia’ where the moth was found. Another person Ishiwatari had named the bacterium Bacillus sotto in 1901 but the name was later considered invalid. BT is a gram-positive and soil-dwelling bacteria and soil staying bacterium. It is also present in the gut of caterpillars of different kinds of moths and butterflies as well as on leaf surface oceanic conditions, creature dung, bug-rich climate and flour factories, and grain storerooms.

Hence, the correct answer is option (C).

Note: We get to know with this answer that the activated toxin binds to the surface of midgut epithelial cells and creates pores that cause cell swelling and lysis and eventually cause the death of the insect. These crystal proteins are poisonous to unmistakable types of bugs yet innocuous or harmless to people and the regular adversaries of many crop pests.