Which one of the following pairs is wrongly matched ?

Options

A. Nitrosomonas : Nitrifying and chemo lithotrophic bacteria .
B. Rhodospirillum : Nitrogen fixation bacteria and photo - organotrophs bacteria.
C. E coli : used in genetic engineering and pollution indicating bacteria
D. Pseudomonas : responsible for food poisoning and purity of Ganga water.

Answer

To solve the question of identifying the wrongly matched pair, we will analyze each option provided in the question.

### Step-by-Step Solution:

1. **Identify the Options**:
We have four pairs to analyze:
- Option 1: Nitrosomonas - Nitrifying bacteria
- Option 2: Rhodospirillum - Nitrogen fixation bacteria and Photo-organotrophs
- Option 3: E. coli - Genetic engineering and pollution indicating bacteria
- Option 4: Pseudomonas - Food poisoning and purity of Ganga water

2. **Analyze Option 1**:
- **Nitrosomonas** is indeed a nitrifying bacterium that converts ammonia into nitrites. This pair is correctly matched.

3. **Analyze Option 2**:
- **Rhodospirillum** is a genus of purple non-sulfur bacteria that can perform nitrogen fixation and are also photo-organotrophs. This pair is also correctly matched.

4. **Analyze Option 3**:
- **E. coli** (Escherichia coli) is widely used in genetic engineering and is a common indicator of fecal contamination in water. This pair is correctly matched.

5. **Analyze Option 4**:
- **Pseudomonas** is a genus of bacteria known for its role in various environmental processes, including some species that can cause food poisoning. However, the claim that it is responsible for the "purity of the Ganga water" is misleading. Pseudomonas is not specifically known for maintaining the purity of water bodies like the Ganga. Therefore, this pair is incorrectly matched.

### Conclusion:
The wrongly matched pair is **Option 4: Pseudomonas - Food poisoning and purity of Ganga water**.