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

Options

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

Answer

**Step-by-Step Solution:**

1. **Understanding Bacillus thuringiensis (Bt):**
- Bacillus thuringiensis is a bacterium known for its ability to produce protein crystals that contain insecticidal proteins. These proteins are toxic to certain insects but are harmless to plants and the bacteria itself.

2. **Formation of Protein Crystals:**
- During its life cycle, Bacillus thuringiensis produces these protein crystals, which are essentially inactive forms of the toxin, referred to as protoxins.

3. **Activation of Protoxins:**
- The activation of these protoxins occurs in the acidic environment of the insect's foregut. When the insect consumes the bacteria, the acidic pH activates the protoxins, converting them into their active form.

4. **Binding to Insect Cells:**
- Once activated, the insecticidal proteins bind to the epithelial cells lining the midgut of the insect. This binding is crucial for the toxin's effectiveness.

5. **Effect on the Insect:**
- After binding to the midgut cells, the toxin disrupts the cells' function, leading to the eventual death of the insect. This process is specific to certain insect pests, making Bacillus thuringiensis a targeted biopesticide.

6. **Genetic Coding:**
- The insecticidal protein is coded by several genes, including the well-known cry gene, which is responsible for producing the toxin.

**Conclusion:**
The correct answer to the question is that the protein binds with epithelial cells of the midgut of insect pests, ultimately killing them.

---