Which of the following bacteria live in the root nodules of plants?

Options

A. Azotobacter
B. Penicillium
C. Rhizobium
D. Mycobacterium

Explanation

To solve the question "Which of the following bacteria live in the root nodules of plants?", we will analyze each option provided:

### Step 1: Understand the Question
The question asks us to identify which bacteria are known to inhabit the root nodules of plants. Root nodules are specialized structures formed by certain plants, particularly legumes, in association with specific bacteria that help in nitrogen fixation.

### Step 2: Analyze the Options
We have four options to consider:
1. **Azotobacter** - This bacterium is known for its role in nitrogen fixation but is typically found in the soil rather than in root nodules.
2. **Penicillium** - This is a genus of fungi, not bacteria. It is primarily known for its use in antibiotic production and food processing, such as cheese making.
3. **Rhizobium** - This is a genus of bacteria that specifically forms symbiotic relationships with leguminous plants, living in their root nodules and aiding in nitrogen fixation.
4. **Mycobacterium** - This genus includes bacteria that can cause diseases in humans and animals, such as tuberculosis. They are not associated with plant root nodules.

### Step 3: Identify the Correct Answer
From the analysis, we can conclude that the only bacteria that live in the root nodules of plants is **Rhizobium**. This bacterium is crucial for the nitrogen-fixing process in legumes, which enhances soil fertility.

### Final Answer
The correct answer is **Rhizobium**.

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