Question

Denitrification is carried out by
(a) Nitrosomonas
(b) Nitrosococcus
(c) Nitrobacter
(d) Pseudomonas

Answer 1

Hint: This process results in a decrease of nitrate in the soil. This is considered a wasteful process as it removes nitrates that are essential for plant growth from the soil. Another example of a microorganism that performs denitrification is Thiobacillus denitrificans. The bacteria which performs denitrification as asked in the question is a Gram- negative aerobic bacteria isolated first in Austria.

Complete Step by Step Answer:
Denitrification is a microbial process where nitrates are reduced to form nitrogen ${ N }_{ 2 }$ and nitrogen oxide ${ N }_{ 2 }{ O }$. The microbes are aerobic under normal conditions but switch to anaerobic during low ${ O }_{ 2 }$ availability. They use $NO_{ 3 }$ as the final electron acceptor in the electron transport chain to produce energy.
This process is very useful for removing $NO_{ 3 }$ from wastewater during sewage treatment. But normally it is considered harmful as it releases greenhouse gases like ${ N }_{ 2 }{ O }$ and ${ NO }$ into the atmosphere.
There are many microbes that perform denitrification such as Paracoccus denitrificans, Pseudomonas, Thiobacillus, etc.
So, the correct option is ‘Pseudomonas’.

Additional information:
Now, let us discuss the other microbes given in the options.
- Nitrosomonas: Oxidation of ammonia into nitrite.
- Nitrosococcus: Oxidation of ammonia into nitrite.
- Nitrobacter: Oxidation of nitrite into nitrate.
All these processes come under nitrification and these bacteria are called nitrifying bacteria. They are chemoautotrophs.

Note: The process of conversion of nitrogen ${ N }_{ 2 }$ to ammonia ${ NH }_{ 4 }$ is called nitrogen fixation. Nitrogen is also fixed by lightning that converts ${ N }_{ 2 }$ into oxides of nitrogen. The fumes from industries and automobiles also have nitrogen oxides. The decomposition of organic ${ N }_{ 2 }$ of dead plants and animals into ammonia is called ammonification. Various fungi and prokaryotic bacteria perform this process to obtain energy through it.