What is true about Bt toxin?

Options

A. The inactive protoxin gets converted into active form in the insect gut
B. Bt protein exists as active toxin in the Bacillus
C. The activated toxin enters the ovaries of the pest to sterilise it and thus prevent its multiplication
D. The concerned Bacilllls has antitoxins

Answer

### Step-by-Step Solution:

1. **Understanding Bt Toxin**: Bt toxin is derived from the bacterium *Bacillus thuringiensis*. This bacterium produces protein crystals that contain insecticidal properties.

2. **Pro-toxin Activation**: The protein crystals produced by *Bacillus thuringiensis* are initially in an inactive form known as pro-toxins. These pro-toxins do not harm the bacterium itself.

3. **Ingestion by Insects**: When insects consume the *Bacillus thuringiensis*, they ingest these pro-toxins along with the bacteria.

4. **Activation in Insect Gut**: Inside the insect gut, the alkaline pH triggers the conversion of the inactive pro-toxins into their active form. This means that the pro-toxins are activated in the gut of the insect.

5. **Mechanism of Action**: The activated toxins bind to the midgut epithelial cells of the insect. This binding creates pores in the cells, leading to an influx of water and ultimately causing the cells to swell and burst, which results in the death of the insect.

6. **Genetic Engineering Application**: The genes responsible for producing these toxins (known as cry genes) have been isolated and inserted into genetically modified plants. These plants can then produce the insecticidal proteins themselves, providing a natural form of pest control.

7. **Evaluating the Options**:
- **Option A**: The inactive pro-toxin gets converted into active form in the insect gut. (True)
- **Option B**: The Bt protein exists as active toxin in the bacillus. (False)
- **Option C**: The activated toxin enters the ovary of the pest to sterilize it. (False)
- **Option D**: The concerned Bacillus has antitoxins. (False)

8. **Conclusion**: The correct statement about Bt toxin is that the inactive pro-toxin gets converted into active form in the insect gut.