Which of the following bacteria can fix atmospheric nitrogen in free state?

Both 2 and 3

The correct answer is Option (4) – Both 2 and 3

Biofertilizers are living organisms that enhance the nutrient content of the soil. They primarily derive from bacteria, fungi, and cyanobacteria. Example involves the formation of nodules on the roots of leguminous plants through a symbiotic partnership with Rhizobium bacteria. These bacteria play a crucial role in converting atmospheric nitrogen into organic forms, which can then be utilized by the plant as a nutrient source. A

There are other types of bacteria, such as Azospirillum and Azotobacter, capable of fixing atmospheric nitrogen while free-living in the soil. This activity serves to augment the nitrogen levels within the soil, further enriching its nutrient content.

Cyanobacteria, also known as blue-green algae, are autotrophic microorganisms found in various aquatic and terrestrial environments. Many cyanobacteria species, such as Anabaena, Nostoc, and Oscillatoria, possess the remarkable ability to fix atmospheric nitrogen. This capability makes them valuable contributors to soil fertility. In particular, in paddy fields, cyanobacteria play a significant role as biofertilizers by converting atmospheric nitrogen into organic forms that can be readily utilized by plants.