Milk is converted into curd by :

Options

A. Acetobacter aceti
B. Bacillus megatherium
C. Xanthomonas citri
D. None of these

Answer

To solve the question "Milk is converted into curd by:", we need to identify the correct bacterium responsible for this process. Let's break down the solution step by step.

### Step-by-Step Solution:

1. **Understanding the Process**:
- Milk is converted into curd through a process called fermentation. This process involves the conversion of lactose (sugar present in milk) into lactic acid.

**Hint**: Recall that fermentation is a metabolic process that occurs in the absence of oxygen.

2. **Identifying the Bacterium**:
- The primary bacterium responsible for this fermentation in milk is **Lactobacillus**. This bacterium ferments lactose to produce lactic acid, which causes the milk to sour and thicken, forming curd.

**Hint**: Think about the types of bacteria involved in dairy fermentation.

3. **Evaluating the Options**:
- Now, let's evaluate the options provided:
- **Azetobacter aceti**: This bacterium is involved in vinegar production, not curd.
- **Bacillus megatherium**: This is used in the production of synthetic penicillin, not curd.
- **Xanthomonas citri**: This bacterium causes citrus canker and is harmful to citrus plants, not related to curd production.
- **None of these**: Since none of the listed bacteria are responsible for curd formation, this option is correct.

**Hint**: Consider the specific roles of each bacterium listed in the options.

4. **Conclusion**:
- Since Lactobacillus is not listed among the options, the correct answer to the question is **none of these**.

### Final Answer:
Milk is converted into curd by: **None of these**.