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Difference between Azotobacter and Azospirillum

Azotobacter and Azospirillum: An Introduction

Last updated date: 16th Mar 2023
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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 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 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



Azotobacter is free living.

Azospirillum is present in associative symbiotics in the roots of plants.

They are Aerobic.

They are Microaerophillic.

They are oval or spherical bacteria.

They are rod-shaped bacteria.

Azotobacter is a genus that belongs to the rhodospirillaceae family.

Azospirillum is a genus that belongs to the pseudomonadaceae family.

Azotobacter, however, also supplies nitrogen to plants in the form of ammonium. However, this does not directly benefit plants.

Azospirillum directly influences plant development. These are necessary for the development of plants.

Azospirillum Images

Azospirillum is recognized for its white, solid and soft growth on medium containing Petri dishes.

Azospirillum spp

Azospirillum spp

Azospirillum spp Lab

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.


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.  

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FAQs on Difference between Azotobacter and Azospirillum

1. Does azospirillum require oxygen or not?

Azospirillum is a member of the bacterial species that fix nitrogen. Additionally, the procedure uses energy. However, this bacteria can function to some extent in both aerobic and anaerobic environments. Only when oxygen is not present does nitrogen-fixing take place. The soil and plant parts have oxygen. However, these bacteria require anaerobic conditions. So, the bacteria have leghaemoglobin molecules. Leghaemoglobin, which binds to oxygen molecules to maintain the oxygen in plant roots, creates an environment that is appropriate and oxygen-free for bacterial operation.

2. What exactly is an azotobacter biofertilizer?

Most crops are grown using azotobacter; a nitrogen-fixing free-living bacteria, as a biofertilizer. Plants are unable to directly use environmental nitrogen. Nitrogen exists in the form of N in the atmosphere. These bacterias aid plants in absorbing nitrogen from the air in the form of nitrate and ammonia. These microorganisms are used to create biofertilizers. The biofertilizer has a six-month shelf life after the date of manufacturing. The process requires locally accessible manufacturing equipment, plants and raw materials.

3. How is the azospirillum classified?

Similarities and differences between various creatures are used to classify them. Those with similar characteristics are included in the same category. Starting with prokaryotes, azospirillum is categorised fundamentally. Bacteria and archaea are the two domains of the prokaryotic groupings. Proteobacteria, gram-positive bacteria and nonproteobacteria gram-negative bacteria are further members of the domain bacteria. Alphaproteobacteria, deltaproteobacteria, gammaproteobacteria, epsilon proteobacteria and beta proteobacteria are the five different kinds of proteobacteria. The alpha-proteobacteria group includes azospirillum. Alphaproteobacteria are known for their unique morphologies and ability to flourish at extremely low nutrition levels (stalks or buds).

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