Microbes that enrich the nutrient quality of soil by enhancing the availability of nutrients to soil are called biofertilisers.
Rhizobium Symbiotic Bacterium that lives in the root nodules of leguminous plants. Fixes atmospheric nitrogen into organic form which is used by plants as nutrient
Azotobacter and Azospirullum Free living bacteria of the soil fix the atmospheric nitrogen making it available to the plants.
Mycorrhiza – Symbiotic association of Fungi – Glomus and plant roots – Absorb Phosphorus from soil and passes it to the plant.
Anabaena, Nostoc, Oscillatoria – Cyanobacteria – Autotrophic bacteria commonly called blue green algae , found in aquatic and terrestrial environments. They fix atmospheric nitrogen , add organic matter to the soil and increase fertility.