Bacillus thuringiensis (Bt) strains have been used for designing novel

Options

A. (a) bio-insecticidal plants
B. (b) biomineralization process
C. (c) biofertilizers
D. (d) bio-metallurgical techniques

Answer

### Step-by-Step Solution:

1. **Understanding Bacillus thuringiensis (Bt)**:
- Bacillus thuringiensis is a gram-positive bacterium known for its ability to produce insecticidal proteins.

2. **Production of Protoxin**:
- The bacterium produces crystalline proteins that contain a protoxin. This protoxin is produced by a specific gene known as the cry gene.

3. **Activation of the Toxin**:
- When the protoxin is ingested by pests, it encounters the alkaline conditions in the gut of the pest. This environment activates the protoxin, converting it into a potent toxin.

4. **Mechanism of Action**:
- The activated toxin creates pores in the gut cells of the pest, leading to cell lysis and ultimately causing the death of the pest.

5. **Genetic Engineering Application**:
- Scientists have utilized genetic engineering techniques to isolate the cry gene from Bacillus thuringiensis and transfer it into plants. These genetically modified plants can then produce the protoxin themselves.

6. **Pest Resistance**:
- When pests consume these genetically modified plants, the protoxin is activated in their alkaline gut, leading to pest mortality. This makes the plants resistant to pest damage.

7. **Safety for Humans**:
- Importantly, the protoxin remains inactive in humans due to the acidic conditions in the human gut, making this method safe for human consumption.

8. **Conclusion**:
- Therefore, the use of Bacillus thuringiensis strains has led to the development of bio insecticidal plants, which is the correct answer to the question.

### Final Answer:
**Bio insecticidal plants** are the novel applications designed using Bacillus thuringiensis (Bt) strains.

---