The Marthandam hydroelectric project was initiated by: ((MCAER 2014))

✅Explanation: Nitrobacter bacteria play a crucial role in the nitrogen cycle by oxidizing nitrite to nitrate. This process is essential for the availability of nitrogen to plants.

📌 Other Options Explanations:
-Option B: Nitrosomonas bacteria are involved in the conversion of ammonia (NH3) to nitrite (NO2-).
-Option C: Rhizobium bacteria are known for their symbiotic relationship with legumes, fixing atmospheric nitrogen.
-Option D: Azotobacter is another type of free-living nitrogen-fixing bacteria.

🔑Key Points:
-Nitrogen is an essential constituent of many biomolecules like proteins, amino acids, vitamins, hormones, etc.
-The process through which nitrogen is converted into many forms and consecutively passes from the atmosphere to the soil to the organism and then back to the atmosphere is called the nitrogen cycle.
-Many bacteria play an important role in the nitrogen cycle.
-Nitrogen fixation
-In an ecosystem, nitrogen is present as two nitrogen atoms joined together by a triple bond.
-The process of converting nitrogen into ammonia is called nitrogen fixation.
-Ammonification
-The decomposition of organic nitrogen from dead animals and plants into ammonia is called ammonification.
-Some of the ammonia is volatile and re-enters the atmosphere.
-Most of the ammonia is converted into nitrates by soil bacteria.

✏Bacteria (chemoautotrophs) involved in the conversion of ammonia into nitrates (Nitrification):
-Nitrococcus: It oxidizes ammonia (NH3) into nitrites (NO2-).
-Nitrobacter: It oxidizes nitrite (NO2-) into nitrate (NO3-).
-Denitrification
-The process of converting nitrates (NO3-) into nitrogen is called denitrification.
-Pseudomonas and thiobacillus help in denitrification process.
-Rhizobium bacteria
-It helps in fixing atmospheric nitrogen in leguminous plants by converting it into ammonia.
-This bacteria is present in the root nodules of leguminous plants.