Bacillus thuringiensis forms protein crystals which contain insecticidal protein. This protein:

Options

A. does not kill the carrier bacterium which is itself resistant to this toxin
B. binds with epithelial cells of midgut of the insect pest ultimately killing it
C. is coded by several genes including the gene cry
D. is activated by acid pH of the foregut of the insect pest

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 known for their ability to kill certain insect pests.

2. **Nature of the Protein:**
- The insecticidal protein produced by Bacillus thuringiensis is referred to as Bt toxin. It is initially released in an inactive form known as protoxin.

3. **Activation of the Toxin:**
- The activation of the protoxin into its active form occurs in the alkaline pH environment found in the midgut of certain insect pests. This is crucial because the bacteria itself does not get affected by the toxin due to the absence of this alkaline condition.

4. **Mechanism of Action:**
- Once activated, the Bt toxin binds to the epithelial cells of the midgut of the insect. This binding disrupts the gut cells, leading to the death of the insect.

5. **Conclusion:**
- Therefore, the insecticidal protein produced by Bacillus thuringiensis ultimately kills the insect by binding to the epithelial cells of its midgut, which is facilitated by the alkaline pH present in the insect's digestive system.

**Final Answer:**
The protein from Bacillus thuringiensis binds with epithelial cells of the midgut of the insect pest, ultimately killing it.

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