Microbes as bio-fertilizers:

Bio-fertilizers are the micro-organisms which increases the nutrient quality of soil. The main sources of biofertilisers are bacteria, fungi and cyanobacteria.
 

Bacteria as bio-fertilizer:

• Rhizobium in symbiotic association with the roots of leguminous plants converts atmospheric nitrogen into organic and more usable compounds, which is used by the plant as nutrient.
• Some free living bacteria like Azospirillum and Azotobacter fix atmospheric nitrogen while free-living in the soil thus enriching the nitrogen content of the soil.
   

Fungi as bio-fertilizer:

• Mycorrhiza is the symbiotic association of fungi with roots of higher plants. The fungal part absorbs phosphorus from soil and passes it to the plant. They provide many several uses to plant such as, resistance to root born pathogen, tolerance to environmental stress and help in overall plant growth and regulation.
• Cyanobacteria (e.g. Anabaena, Nostoc, Oscillatoria) fix atmospheric nitrogen.
• Blue green algae also add organic matter to the soil and increase its fertility.