Question

Most famous nitrogen-fixing bacteria/ biofertilizer is
(a)Nitrobacter
(b)Nitrosomonas
(c)Nitrococcus
(d)Rhizobium

Answer 1

They are commonly found in root nodules of leguminous plants and are biological cells which are prokaryotic microorganisms and a few micrometers in length with several shapes ranging from spheres to rod and spirals. They can live inside the soil and the human gut. They are microscopic and can survive in diverse conditions.

Complete answer:
Rhizobium is the most famous nitrogen-fixing bacteria or biofertilizer. It is an endosymbiotic nitrogen-fixing bacteria which consists of roots of legumes and it is colonized within the root nodules in plant cells. They cannot fix nitrogen independently and are motile and gram-negative non-sporulating rods. They produce infection in the nodules in the legume and are found in the soil where they fix nitrogen gas from the atmosphere and convert it into a useful form of nitrogen. The nitrogen is exported from the nodules which are used as the growth in the legume and the nodule breaks down and releases the rhizobium back into the soil where they live and the legume dies or reinfects a new legume host.

Additional Information: Nitrobacter: It is a gram-negative, chemoautotrophic bacteria. They are non-motile and reproduce by the method of budding or binary fission. It consists of aerobes which are obligate and consist of a double time of about 13 hours. They helped in the nitrogen cycle by oxidizing nitrite into nitrate in soil and various Marine systems. It provides energy for carbon fixation and it uses energy from the nitrite ions oxidation to fulfill their energy needs.
Nitrosomonas: It is a gram-negative, chemoautotrophic bacteria that perform the metabolic process of nitrification where it oxidizes ammonia into nitrite. They are useful in polluted water and wastewater treatment which is known as bioremediation. It consists of power generating membranes that are present inside the cells and forms long and thin tubes that use electrons from the oxidation of ammonia for the production of energy.
Nitrococcus: It is a nitrifying bacteria which is used for oxidizing toxic ammonia produced by the shrimp metabolism. they develop naturally in the biofloc systems and depend on nutrient availability and various factors such as temperature and pH which result in temporary accumulation of nitrite.
So, the correct answer is 'Rhizobium'.

Note: Rhizobium was invented by Martinus Willem Beijerinck who explored the mechanism responsible for discovering root nodules that contained microbes. They are diazotrophic in nature and are bacterial symbionts of legume plants.