Which is not correct about methanogens?

Options

A. They are archaebacteria
B. They live in marshy areas
C. Methane is their preferred carbon source
D. They are present in guts of several ruminant animals (cow, buffaloes) and they produce biogas `(CH_(4))` from the dung of these animals.

Answer

To determine which statement is not correct about methanogens, let's analyze each option provided in the question:

1. **They are archaebacteria.**
- Methanogens are indeed classified as archaebacteria. They belong to a group of microorganisms that are distinct from bacteria and are known for their ability to produce methane.

2. **They live in the Morsee area.**
- This statement is unclear. The term "Morsee area" does not correspond to any known ecological or geographical term related to methanogens. Methanogens are typically found in anaerobic environments such as swamps, marshes, and the guts of ruminants, but not specifically in a "Morsee area."

3. **Methane is their preferred carbon source.**
- This statement is incorrect. Methanogens do not use methane as a carbon source; rather, they produce methane as a metabolic byproduct when they decompose organic matter. Their preferred substrates are usually compounds like carbon dioxide, hydrogen, or acetate.

4. **They are present in the guts of several luminous animals, i.e., example cows and buffaloes, and they produce biogas, i.e., methane from the dung of these animals.**
- This statement is correct. Methanogens are indeed found in the digestive systems of ruminants like cows and buffaloes, where they help in breaking down food and produce methane as a byproduct.

Based on the analysis:

**The statement that is not correct about methanogens is Option 3: "Methane is their preferred carbon source."**

### Step-by-Step Solution:
1. Identify the characteristics of methanogens.
2. Analyze each option provided in the question.
3. Confirm the correct classification of methanogens as archaebacteria.
4. Evaluate the ecological niches where methanogens are found.
5. Determine the metabolic processes of methanogens, specifically their carbon sources.
6. Conclude which statement is incorrect based on the analysis.