What is the group of bacteria found in both the rumen of cattle and sludge of sewage treatment?

Explanation

### Step-by-Step Solution:

1. **Identify the Context**: The question asks for a specific group of bacteria that exists in two distinct environments: the rumen of cattle and the sludge in sewage treatment.

2. **Understand the Environments**:
- **Rumen of Cattle**: This is a part of the digestive system of cattle where fermentation occurs, allowing them to break down cellulose from plant material.
- **Sludge of Sewage Treatment**: This is the solid waste material that settles at the bottom of sewage treatment plants, where anaerobic digestion takes place.

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