What is true of Bt toxin ?

Options

A. The concentrated bacillus has antitoxins
B. The inactive protoxin gets converted into active form in the insect gut
C. Bt protein exists as active toxin in the bacillus
D. The activated toxin enters the ovaries of the pest to sterilize it and this prevents its multiplication.

Answer

### Step-by-Step Solution:

1. **Understanding Bt Toxin**:
- Bt toxin is produced by the bacterium Bacillus thuringiensis, which is a gram-positive bacterium. It is specifically used for controlling plant-feeding insects.

2. **Mechanism of Action**:
- The toxin exists in an inactive form known as a protoxin within the bacterium. When an insect consumes the bacteria, the high pH environment of the insect gut activates the protoxin, converting it into the active Bt toxin.

3. **Effects on Insects**:
- Once activated, the Bt toxin binds to the gut cells of the insect, causing swelling and eventually leading to cell lysis (breaking down of cells). This results in the insect's death within a few days.

4. **Evaluating the Options**:
- **Option A**: "The concentrated bacillus has antitoxins."
- This is incorrect because Bacillus thuringiensis does not produce antitoxins; it produces the toxin itself.

- **Option B**: "The inactive protoxin gets converted into active form in the insect gut."
- This is correct. The protoxin is harmless to the bacteria and becomes active in the insect gut due to the high pH.

- **Option C**: "Bt protein exists as active toxin in the bacillus."
- This is incorrect. The Bt protein exists as an inactive protoxin in the bacterium.

- **Option D**: "The activated toxin enters the ovaries of the pest."
- This is incorrect because the activated toxin primarily affects the gut of the insect, not its reproductive organs.

5. **Conclusion**:
- The correct statement about Bt toxin is **Option B**: "The inactive protoxin gets converted into active form in the insect gut."