Question

Which of the following bacterium causes denitrification?
(a)Azotobacter
(b)Nitrobacter
(c)Nitrosomonas
(d)Pseudomonas

Answer 1

Hint: Bacteria that cause denitrification to convert nitrates in the soil to free nitrogen that escapes from the soil and cannot be assimilated by the plants. There are other bacteria that assimilate free nitrogen in the air and soil and convert it into products that can be taken up by the plant.

Complete answer:
Denitrifying bacteria are microorganisms that convert nitrates in the soil to free atmospheric nitrogen. This nitrogen cannot be absorbed and assimilated by plants.
- Pseudomonas bacteria under anaerobic conditions reduce the fixed nitrogen (nitrate).
- Denitrification occurs when there is a lack of oxygen available for aerobic respiration. The nitrate is used instead of oxygen as a terminal electron acceptor. The nitrate is reduced to nitrite, nitric oxide, nitrous oxide, or nitrogen gas.
- The chemical reaction can be denoted as ${ 2NO }^{ - }_{ 3 }\quad \rightarrow \quad { 2NO }_{ 2 }^{ - }\quad \rightarrow \quad 2NO\quad \rightarrow \quad { N }_{ 2 }O\quad \rightarrow \quad { N }_{ 2 }$

Additional information: - Other examples of denitrifying bacteria are Thiobacillus denitrificans, Micrococcus denitrificans, Serratia, Pseudomonas, etc.
- Azotobacter is an example of diazotroph or nitrogen-fixing bacteria. Nitrobacter and Nitrosomonas are nitrifying bacteria that oxidize ammonium to nitrate and nitrite.

So, the correct answer is ‘Pseudomonas’.

Note: - Nitrifying and denitrifying bacteria form the components of the Nitrogen Cycle.
- Although denitrification is a process necessary to complete the Nitrogen cycle, excess usage of nitrogen fertilizers has caused nitrogen to become a pollutant. Its presence may lead to acid rain, eutrophication, and algal blooms.