In nitrogen cycle, Thiobacillus sp bacteria

Options

A. fixes nitrogen
B. produces elemental nitrogen
C. oxidises ammonium to nitrate
D. transfers elemental nitrogen

Answer

### Step-by-Step Solution:

1. **Understanding the Nitrogen Cycle**: The nitrogen cycle is a series of processes by which nitrogen and its compounds are interconverted in the environment and in living organisms. It includes nitrogen fixation, nitrification, denitrification, and ammonification.

2. **Role of Thiobacillus sp.**: Thiobacillus is a genus of bacteria that plays a role in the nitrogen cycle, particularly in the denitrification process. However, it is important to clarify that Thiobacillus does not fix nitrogen or oxidize ammonia.

3. **Nitrogen Fixation**: This is the first step in the nitrogen cycle where atmospheric nitrogen (N₂) is converted into ammonia (NH₃). This process can occur through biological means (by nitrogen-fixing bacteria) or non-biological means (like lightning).

4. **Nitrification**: After nitrogen fixation, ammonia is oxidized to nitrite (NO₂⁻) and then to nitrate (NO₃⁻). This process is carried out by specific bacteria such as Nitrosomonas (which oxidizes ammonia to nitrite) and Nitrobacter (which oxidizes nitrite to nitrate).

5. **Denitrification**: This is the process where nitrates are reduced back to nitrogen gas (N₂), completing the nitrogen cycle. Thiobacillus sp. is involved in this process, where it helps convert nitrate into nitrogen gas.

6. **Conclusion**: Therefore, the role of Thiobacillus sp. in the nitrogen cycle is primarily as a denitrifying bacterium that converts nitrate into nitrogen gas, rather than fixing nitrogen or oxidizing ammonia.

### Final Answer:
Thiobacillus sp. bacteria play a role in the nitrogen cycle as denitrifying bacteria, converting nitrates into nitrogen gas, thus completing the cycle.

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