Usage of Azotobacter and Azospirillum

They are used as biofertilizers and seed inoculants for non-leguminous plants for the following reasons:

• They can convert atmospheric nitrogen into ammonia.
• They have a crucial role in maintaining the usable form of N₂ , a vital macronutrient in soil.
• They can help to mineralise other nutrients like phosphorus, carbon, sulphur, overall increasing soil fertility.
• They increase uptake of macronutrients like N, P and some micronutrients like Zn, Fe.
• They release vital phytohormones and other biologically active substances to promote growth of crop plants.
• They also stimulate flowering, rooting, foliage formation, seed vigour.
• These microorganisms help in biological remediation of heavy metals and other soil pollutants.
• Azospirillum spp. can produce antioxidants to mitigate oxidative stress of plants.
• These bacteria induce plant defence mechanisms to fight various biotic and abiotic stresses.
• Azotobacter spp. are also used in industrial production of important biopolymers like- alginate (have biomedical applications), poly 3-hydroxybutyrate (used in biodegradable plastics) etc.

The main difference between Azotobacter and Azospirillum lies in the way these nitrogen fixers are found in nature. The Azotobacter species are non-symbiotic nitrogen-fixing bacteria, whereas the Azospirillum species are associative rhizobacteria that fix nitrogen. Azotobacter are aerobic, free-living species. They are widely distributed in soils and waters. On the contrary, Azospirillum spp. are microaerophilic and often found in a beneficial association with plants.

They are present either in the rhizospheres or the roots of important crop plants. Both of them are diazotrophs, meaning they are capable of biological nitrogen fixation (BNF). In this article, we will look into the differences between Azotobacter and Azospirillum in detail.