In the case of Bacillus thuringiensis , Bacillus itself is not killed by toxic protein crystals produced by it because

Options

A. Bt toxin protein is not produced in the bacteria
B. Bt toxin protein is produced in very less amount in the bacillus
C. Bt toxin exists as an inactive toxin
D. the bacteria is resistant to the Bt toxin

Answer

To solve the question regarding why Bacillus thuringiensis (Bt) is not killed by the toxic protein crystals it produces, we can break down the reasoning step by step:

### Step-by-Step Solution:

1. **Understanding Bacillus thuringiensis**:
- Bacillus thuringiensis is a soil bacterium known for producing a toxin that is harmful to certain insects.

2. **Nature of the Toxin**:
- The toxin produced by Bacillus thuringiensis is known as Bt toxin. It is produced in the form of crystalline protein.

3. **Inactivity of the Toxin**:
- When the Bt toxin is produced within the bacterial cells, it exists in an inactive form. This means that the toxin does not exert its harmful effects on the bacteria itself.

4. **Crystalline Form**:
- The Bt toxin is stored as crystals which are not bioactive. It is only when the crystals are ingested by certain insects that they are activated and become toxic.

5. **Resistance of the Bacteria**:
- Bacillus thuringiensis has evolved mechanisms that confer resistance to its own toxin, ensuring that it can survive and thrive despite producing the toxin.

6. **Conclusion**:
- Therefore, the reason Bacillus thuringiensis is not killed by the toxic protein crystals it produces is that the Bt toxin exists as an inactive toxin when it is within the bacterial cells.

### Final Answer:
The correct answer is **C: Bt toxin exhibits as an inactive toxin**.