What Is the Difference Between Azotobacter and Azospirillium in Structure Function and Agricultural Importance
Azotobacter is a heterotrophic, naturally occurring, nitrogen-fixing bacterium that may be found in neutral or alkaline soil. Azotobacter chrococcum and Azotobacter beijerinckii are two of the genus' most significant species. These species assist plants in fixing nitrogen. Azotobacter and azospirillum both are bacteria that help in nitrogen fixation in plants. Azospirillum is a soil bacteria that grows in close proximity to the roots of tropical grasses. Azospirillum is a gram-negative motile bacterium found in monocot roots. It utilises expelled nutrients to promote plant development by nitrogen fixation from the atmosphere.
What are Azotobacter and Azospirillum?
Azotobacter
Azotobacter is capable of converting atmospheric nitrogen to ammonia, which is then absorbed and utilised by plants. Due to nitrogenase respiration protection, such bacteria are extremely resistant to oxygen during nitrogen fixation.
This organism has been found in the rhizospheres of a variety of crop plants, including rice, maize, sugarcane, bajra, vegetables, and plantation crops.
Seed inoculated with Azotobacter aids in the uptake of N, P, and micronutrients such as Fe and Zn in wheat; these strains have the potential to improve wheat nutrition.
Azospirillum
Azospirillum is an example of a facultative aerobic nitrogen fixer. Nitrogen is present in the atmosphere that is not directly consumed by the plants. Some prokaryotes such as bacteria help to fix this nitrogen for plants. Plant and living bacteria live in symbiosis association in which plants provide space to the organism and in return bacteria provide fixed nitrogen and nutrients to plants.
Azospirillum is an associative symbiotic nitrogen-fixing bacteria in the soil. These bacteria have an enzyme complex called nitrogenase complex that helps in nitrogen fixation. This is used in biofertilizers to increase the growth of the plant. Azospirillum lipoferum and azospirillum brasilense are two significant species.
Difference Between Azotobacter and Azospirillum
Azospirillum Images
Azospirillum is recognized for its white, solid and soft growth on medium containing Petri dishes.
Azospirillum spp
Azospirillum spp in Lab
Uses of Azotobacter and Azospirillum
Azotobacter is one of the best biofertilizer options for eco-friendly and sustainable crop production due to its ability to improve plant health through nitrogen fixation, growth hormone production, phosphate solubilization, plant disease management, and reclamation of better soil health.
Azospirillum is used as a biofertilizer due to its nitrogen-fixing characteristics. These bacterias help plants in the production of growth substances such as auxin, gibberellin and cytokinin. These are plant growth hormones. Azospirillum is utilised in vegetable crops by seed treatment, eye bud pasting and other methods.
Two Bacterial Examples of Biofertilizer
Bio-fertilizers (living fertilisers) are a combination of microorganisms capable of mobilising nutrients via biological processes. They supply plant nutrients via nitrogen fixation, phosphate solubilization, soil reactivity stability and soil quality enhancement.
Biofertilizers such as rhizobium, azotobacter, azospirillum, Azolla and blue-green algae are widely viable (BGA). Rhizobium, azotobacter, and azospirillum are bacterial examples of biofertilizers.
Conclusion
Azotobacter species are found everywhere in neutral and weakly basic soils, but not in acidic soils. Despite the cold climate, short growing season, and relatively low pH values of these soils, they can be found in Arctic and Antarctic soils. Azotobacter can survive in dry soils for up to 24 years as cysts. Azospirillum can promote plant growth through abiotic stress tolerance mechanisms known as induced systemic tolerance, which are mediated by antioxidants, osmotic adjustment, phytohormone production, and defence strategies such as pathogenesis-related gene expression. The above article is helpful to clarify the concept of azotobacter and azospirillum and the difference between these two bacteria.
FAQs on Difference Between Azotobacter and Azospirillium in Nitrogen Fixation
1. What is the difference between Azotobacter and Azospirillum?
The main difference between Azotobacter and Azospirillum is that Azotobacter is a free-living nitrogen-fixing bacterium, whereas Azospirillum is an associative nitrogen-fixing bacterium that lives in close association with plant roots.
- Azotobacter: Free-living, aerobic, found in neutral to alkaline soils.
- Azospirillum: Associative, microaerophilic, commonly associated with cereal and grass roots.
- Azospirillum also promotes plant growth by producing growth hormones like IAA (Indole-3-acetic acid).
2. What is Azotobacter?
Azotobacter is a free-living, aerobic, nitrogen-fixing bacterium found in soil that converts atmospheric nitrogen into ammonia.
- Belongs to the genus Azotobacter.
- Fixes nitrogen independently without forming symbiotic nodules.
- Commonly found in neutral or alkaline soils.
- Used as a biofertilizer in agriculture.
3. What is Azospirillum?
Azospirillum is a microaerophilic, associative nitrogen-fixing bacterium that lives in close contact with plant roots, especially cereals and grasses.
- Belongs to the genus Azospirillum.
- Forms loose associations with roots but does not form nodules.
- Fixes atmospheric nitrogen under low oxygen conditions.
- Produces plant growth hormones like IAA, gibberellins, and cytokinins.
4. How does Azotobacter fix nitrogen?
Azotobacter fixes nitrogen by converting atmospheric nitrogen (N₂) into ammonia using the enzyme nitrogenase under aerobic conditions.
- Occurs in soil independently of plants.
- Uses high respiratory activity to protect nitrogenase from oxygen damage.
- Produces ammonia that enriches soil fertility.
5. How does Azospirillum help in plant growth?
Azospirillum promotes plant growth by fixing nitrogen and producing plant growth-promoting substances.
- Associates with roots of cereals like wheat and maize.
- Fixes atmospheric nitrogen under microaerophilic conditions.
- Produces hormones such as Indole-3-acetic acid (IAA) that enhance root development.
- Improves nutrient and water uptake.
6. Is Azotobacter symbiotic or free-living?
Azotobacter is a free-living nitrogen-fixing bacterium and does not form a symbiotic relationship with plants.
- Lives independently in soil.
- Does not form root nodules.
- Fixes nitrogen without requiring a host plant.
7. Is Azospirillum aerobic or anaerobic?
Azospirillum is a microaerophilic bacterium, meaning it requires low oxygen levels for optimal nitrogen fixation.
- Grows best under limited oxygen conditions.
- Associates with plant roots where oxygen concentration is lower.
- Protects the enzyme nitrogenase from oxygen damage.
8. What are the similarities between Azotobacter and Azospirillum?
Both Azotobacter and Azospirillum are nitrogen-fixing bacteria used as biofertilizers to improve soil fertility.
- Convert atmospheric nitrogen into usable forms.
- Contain the enzyme nitrogenase.
- Enhance plant growth and crop yield.
- Commonly used in sustainable agriculture.
9. Which crops are associated with Azotobacter and Azospirillum?
Azotobacter is commonly used for vegetables and non-leguminous crops, while Azospirillum is mainly associated with cereals and grasses.
- Azotobacter: Vegetables, cotton, sugarcane, and wheat.
- Azospirillum: Rice, maize, wheat, and other cereals.
- Both are applied as biofertilizers to enhance nitrogen availability.
10. Why are Azotobacter and Azospirillum used as biofertilizers?
Azotobacter and Azospirillum are used as biofertilizers because they fix atmospheric nitrogen and promote plant growth naturally.
- Reduce the need for chemical nitrogen fertilizers.
- Improve soil fertility and crop productivity.
- Enhance root growth and nutrient uptake.
- Support sustainable and eco-friendly agriculture.
