Which of the following bacterium is most commonly used in genetic engineering :

Options

A. E. coli and Agrobacterium
B. Mycobacteria and Salmonella
C. Aspergillus
D. Penicillium

Answer

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks which bacterium is most commonly used in genetic engineering. We need to analyze the options provided.

2. **Identifying Commonly Used Bacteria**: The two bacteria that are most commonly associated with genetic engineering are *Escherichia coli* (E. coli) and *Agrobacterium tumefaciens*.

3. **Analyzing E. coli**:
- *E. coli* is a prokaryotic bacterium that is widely used in laboratories.
- It has a rapid generation time, dividing approximately every 20 minutes, which makes it convenient for experiments.
- It is easy to manipulate genetically, making it a primary choice for cloning and expressing genes.

4. **Analyzing Agrobacterium**:
- *Agrobacterium tumefaciens* is known as a natural genetic engineer.
- It has a plasmid known as the Ti-plasmid (tumor-inducing plasmid) that can transfer genes into plant cells.
- This bacterium is particularly useful for introducing genes into plants, making it significant in plant genetic engineering.

5. **Evaluating Other Options**:
- Other bacteria mentioned, such as Mycobacterium and Salmonella, are pathogenic and not used in genetic engineering.
- Fungi like Aspergillus and Penicillium are also not relevant to bacterial genetic engineering.

6. **Conclusion**: Based on the analysis, the most commonly used bacterium in genetic engineering is *E. coli*, but *Agrobacterium* is also significant for plant genetic engineering. Therefore, the correct answer is *E. coli*.

**Final Answer**: *E. coli* is the most commonly used bacterium in genetic engineering.

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