The key difference between Azotobacter and Azospirillum is that Azotobacter is a genus of bacteria that are mainly aerobic and endophytic diazotrophs. Meanwhile, Azospirillum is a genus of plant growth-promoting bacteria that are microaerophilic and surface-colonizing bacteria.
Azotobacter and Azospirillum are two bacterial genera that are important as nitrogen fixers in the soil. They are mainly soil bacteria that are gram-negative. Moreover, they are free-living bacteria that associate plant roots. They enhance plant growth and development after inoculation. Azotobacter spp are heterotrophic and aerobic, oval or spherical bacteria while Azospirillum spp are microaerophilic and non-fermentative rod-shaped bacteria.
1. Overview and Key Difference
2. What is Azotobacter
3. What is Azospirillum
4. Similarities Between Azotobacter and Azospirillum
5. Side by Side Comparison – Azotobacter vs Azospirillum in Tabular Form
What is Azotobacter?
Azotobacter is a genus of bacteria which consists of aerobic, motile, oval or spherical, free-living soil bacteria. Moreover, Azotobacter form thick-walled cysts and may produce large quantities of capsular slime. Hence, their cysts are more resistant to adverse environmental factors. These bacteria play an important role in nitrogen fixation and participate in the nitrogen cycle in nature.
Azotobacter converts atmospheric nitrogen into ammonia in the soil. Since they are able to fix nitrogen, they are used as biofertilizers. Moreover, Azotobacter is used as food additives and some biopolymers.
What is Azospirillum?
Azospirillum is a genus of microaerophilic, gram-negative, rod-shaped bacteria associated with plant roots. They are commonly known as plant growth-promoting bacteria. They are predominantly surface-colonizing bacteria. Therefore, they form loose associations with the plant surface. Similar to Azotobacter, Azospirillum spp are also nitrogen-fixing free-living bacteria. They belong to the family rhodospirillaceae, which are non-fermentative.
Since Azospirillum can fix nitrogen, it is one of the most widely used free-living nitrogen-fixing microorganisms as inoculants, especially for rice. Under submerged conditions in paddy fields, Azospirillum enhance rice plant growth and yield.
What are the Similarities Between Azotobacter and Azospirillum?
- Both Azotobacter and Azospirillum are bacteria that are diazotrophs.
- They are gram-negative, free-living bacteria.
- Moreover, they are motile bacteria.
- Azotobacter sp and Azospirillum are used as nitrogen-fixing bio-fertilizer.
- Therefore, both are used as bacterial inoculants as plant or soil inoculants.
What is the Difference Between Azotobacter and Azospirillum?
Azotobacter spp are aerobic and endophytic diazotrophs. In contrast, Azospirilla are microaerophilic and predominantly surface-colonizing bacteria. So, this is the key difference between Azotobacter and Azospirillum. Azotobacter is a genus belonging to family; pseudomonadaceae/azotobacteraceae, while Azospirillum is a genus belonging to rhodospirillaceae. Also, Azotobacter spp are oval or spherical bacteria, while Azospirillum spp are rod-shaped bacteria.
Moreover, another difference between Azotobacter and Azospirillum is that Azotobacter spp are important as nitrogen-fixing inoculants, biofertilizers, food additives, and some biopolymers while Azospirillum spp are mainly important as plant growth-promoting bacteria. Furthermore, Azotobacter spp are endophytic diazotrophs A while Azospirilla are predominantly surface-colonizing bacteria.
Below infographic summarizes the difference between Azotobacter and Azospirillum.
Summary – Azotobacter vs Azospirillum
Azotobater and Azospirillum are two genera of free-living, nitrogen-fixing bacteria. They are gram-negative, motile soil bacteria which promote plant growth and development. Azotobacter spp are aerobic and endophytic diazotrophs. In contrast, Azospirillum spp are microaerophilic and predominantly surface-colonizing bacteria. Thus, this is the key difference between Azotobacter and Azosprillium.
1. “Azotobacter cells” By DAN H. JONES – JONES D. H. FURTHER STUDIES ON THE GROWTH CYCLE OF AZOTOBACTER // JOURNAL OF BACTERIOLOGY, 1920, VOL. 5, NO. 4 Р. 325-341  (Public Domain) via Commons Wikimedia