Question

Which one of the following is denitrifying bacteria?
A. Nitrosomonas
B. Pseudomonas
C. Azotobacter
D. Nostoc

Answer 1

Hint:- Denitrification the process by which nitrogen containing compounds are metabolized to release gaseous nitrogen. Denitrification is a part of the nitrogen cycle and occurs with the help of certain bacteria of various phyla.

Complete step-by-step solution:- Denitrification is a process that involves conversion of nitrites in the soil to molecular nitrogen. The nitrogen thus formed is released back into the atmosphere to maintain the nitrogen balance of the ecosystem.
Pseudomonas is a gram negative bacteria that belongs to the family Pseudomonadaceae. They are present in various habitats. Almost all species of the genus are aerobic respirators and are naturally resistant to antibiotics like penicillin. This resistance to antibiotics is because of well-developed efflux pumps that pump out the antibiotics from their system. Pseudomonas is a very useful bioremediating agent. Pseudomonas contributes to the nitrogen cycle by acting as a denitrifying bacterium. It converts nitrate to molecular nitrogen.
Nitrosomonas is a Gram-negative rod-shaped bacterium. These organisms are known to convert ammonia into nitrites by a process called nitritation. Nitrosomonas increase the amount of nitrogen available to plants. These bacteria are very useful in bioremediation – a process that involves waste, water and soil treatment using microorganisms. Nitrosomonas are not involved in denitrification.
Azotobacter is a gram negative bacterium found in soils and water. Sometimes, they are present in association with certain plants. Azotobacter are indispensable to the nitrogen cycle. Molecular nitrogen from the atmosphere cannot be taken up by the plants. It has to be converted to ammonium ions for uptake by plants. Azotobacter functions to convert molecular nitrogen to ammonium ions and makes it available to plants. This process is called Nitrogen fixation.
Nostoc is a cyanobacteria capable of performing photosynthesis. It belongs to a family called Nostocaceae and is found in freshwater and saltwater habitats, in soil and on moist rocks. Nostoc comprises specialized cells called heterocyst. These cells help to provide nitrogen to the plant hosts of this species of bacteria.
Therefore, it can be concluded from the above discussion that Pseudomonas is a denitrifying bacterium.
Hence option (b) is correct.

Note:- : Denitrification is an important part of the nitrogen cycle, where molecular nitrogen is released in the atmosphere. This process generally takes place in conditions where oxygen concentration is poor. Denitrifying bacteria helps to bring about the process. These bacteria carry out denitrification as part of their respiratory process where they reduce oxygenated forms of nitrogen. Denitrification can be used to remove nitrogen from sewage treatment plants and reduce groundwater pollution.