Bacillus thuringiensis forms protein crystals which contain insectidical protein. This protein

Options

A. binds with epithelial cells of midgut of the insect pest ultimately killing it
B. is activated by acidic pH of the gut of the insect pest
C. does not kill the carrier bacterium which is itself resistant to this toxin
D. all of these

Answer

**Step-by-Step Solution:**

1. **Understanding Bacillus thuringiensis (Bt):**
- Bacillus thuringiensis is a bacterium that produces protein crystals containing insecticidal proteins. These proteins are toxic to certain insect pests.

2. **Mechanism of Action:**
- When an insect ingests the protein crystals, the alkaline environment of the insect's mid-gut activates the protein. This is a crucial step as the protein is inactive when inside the bacterium.

3. **Binding to Epithelial Cells:**
- Once activated, the insecticidal protein binds to the epithelial cells lining the mid-gut of the insect. This binding is essential for the subsequent steps in the mechanism of action.

4. **Formation of Pores:**
- The binding of the protein to the epithelial cells leads to the formation of pores in the gut cells. This disrupts the integrity of the gut lining.

5. **Consequences of Pore Formation:**
- The formation of these pores causes the gut cells to swell and eventually leads to the death of the insect due to loss of gut function and other physiological disruptions.

6. **Resistance to the Toxin:**
- Importantly, Bacillus thuringiensis itself is resistant to the insecticidal protein it produces. This means that while the protein is lethal to certain insects, it does not harm the bacterium that produces it.

7. **Conclusion:**
- The correct answer to the question is that the protein binds with epithelial cells of the mid-gut of the insect pest, ultimately killing it.

**Final Answer:** The protein binds with epithelial cells of the mid-gut of the insect pest, ultimately killing it.

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