Which among the following is autotrophic microbe which can fix atmospheric nitrogen ?

All of these

The correct answer is Option (4) -All of these

Cyanobacteria, also known as blue-green algae, are a group of photosynthetic bacteria that are commonly found in various aquatic and terrestrial environments, including paddy fields. These microbes play a crucial role in enhancing soil fertility and promoting plant growth through their ability to fix atmospheric nitrogen.

Cyanobacteria are autotrophic microbes widely distributed in aquatic and terrestrial environments many of which can fix atmospheric nitrogen, e.g. Anabaena, Nostoc, Oscillatoria, etc. In paddy fields, cyanobacteria serve as an important biofertiliser. Blue green algae also add organic matter to the soil and increase its fertility. Currently, in our country, a number of biofertilisers are available commercially in the market and farmers use these regularly in their fields to replenish soil nutrients and to reduce dependence on chemical fertilisers.