An example of symbiotic bacterium is
1.erwinia amylovora
2.Rhizobium leguminocearum
3.Xanthomonas campestris
4.Agrobacterium tumefaciens

Options

A. erwinia amylovora
B. Rhizobium leguminocearum
C. Xanthomonas campestris
D. Agrobacterium tumefaciens

Answer

To determine an example of a symbiotic bacterium from the given options, we can follow these steps:

### Step 1: Understand the concept of symbiotic bacteria
Symbiotic bacteria are those that engage in a symbiotic relationship, where both the bacteria and their host benefit from the association. A common example of this is nitrogen-fixing bacteria that live in the root nodules of leguminous plants.

**Hint:** Look for bacteria that have a mutualistic relationship with plants.

### Step 2: Analyze the first option: Erwinia amylovora
Erwinia amylovora is known to be a pathogenic bacterium that causes fire blight disease in plants. Since it does not provide any benefit to its host, this option is incorrect.

**Hint:** Consider whether the bacteria cause disease or provide benefits to the host.

### Step 3: Analyze the second option: Rhizobium leguminosarum
Rhizobium leguminosarum is a well-known symbiotic bacterium that fixes atmospheric nitrogen in the root nodules of leguminous plants. This relationship is beneficial for both the bacteria and the plants, making this option a strong candidate for being the correct answer.

**Hint:** Identify bacteria that fix nitrogen and have a beneficial relationship with plants.

### Step 4: Analyze the third option: Xanthomonas campestris
Xanthomonas campestris is another pathogenic bacterium that causes black rot disease in cruciferous plants. Similar to the first option, it does not establish a mutualistic relationship, thus making this option incorrect.

**Hint:** Remember that symbiotic bacteria should not cause diseases.

### Step 5: Analyze the fourth option: Agrobacterium tumefaciens
Agrobacterium tumefaciens is known for causing crown gall disease in plants. While it interacts with plants, it does not provide a mutual benefit; instead, it induces tumor formation. Therefore, this option is also incorrect.

**Hint:** Evaluate whether the bacteria help or harm the plant.

### Conclusion
After analyzing all the options, the only bacterium that fits the criteria of being a symbiotic bacterium is **Rhizobium leguminosarum**.

**Final Answer:** 2. Rhizobium leguminosarum