The bacterium Bacillus thuringiensis is widely used in contemporary biology as

Options

A. Source of industrial enzyme
B. Insecticide
C. Indicator of water pollution
D. Agent for production of diary products.

Answer

**Step-by-Step Solution:**

1. **Identify the Bacterium**: The question refers to the bacterium Bacillus thuringiensis. It is important to know its characteristics and applications in biology.

2. **Understand the Characteristics**: Bacillus thuringiensis is a gram-positive bacterium. This means that it retains a blue color when subjected to gram staining, indicating its cell wall structure.

3. **Explore its Applications**: The primary application of Bacillus thuringiensis in contemporary biology is as a pesticide. It is widely used in agriculture to control pest populations.

4. **Mechanism of Action**: Bacillus thuringiensis produces a protein toxin during its sporulation phase. This toxin is known to block the gut of certain plant-feeding insects, leading to their death.

5. **Conclusion**: Based on the information gathered, the correct answer to the question is that Bacillus thuringiensis is widely used as an insecticide.

**Final Answer**: The bacterium Bacillus thuringiensis is widely used in contemporary biology as an insecticide (Option B).

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