What is the Difference Between Azospirillum and Azotobacter

The main difference between Azospirillum and Azotobacter is that Azosprillum is a microaerophilic and surface colonizing bacteria whereas Azotobacter is an aerobic, soil-dwelling bacteria.

Azospirirllum and Azotobacter are two types of Gram-negative, free-living bacteria that promote plant growth. Therefore, both types of bacteria are important in nitrogen fixation.

Key Areas Covered

1. What is Azospirirllum
   • Definition, Features, Importance
2. What is Azotobacter
   • Definition, Features, Importance
3. Similarities Between Azospirillum and Azotobacter
   • Outline of Common Features
4. Difference Between Azospirillum and Azotobacter
   • Comparison of Key Differences

Key Terms

Azospirirllum, Azotobacter, Nitrogen Fixing Bacteria

What is Azospirirllum

Azospirilum is a Gram-negative, microaerophilic, non-fermentative, and nitrogen-fixing bacterial genus from the family of Rhodospirillaceae. As this bacterium is Gram-negative, it does not form spores. It also has an oblong-rod shape. Azospirilum bacteria usually have one flagellum or sometimes they have multiple flagella. Therefore, they move faster. Azospirilum is an aerobic bacterium. However, many of the Azospirilum bacteria are microaerobic diazotrophs, meaning, under low oxygen conditions, they can change inert nitrogen from the air into biologically usable forms.

Figure 1: Azospirilum Promotes the Growth of Fine Hair Roots

Furthermore, the three species of the genus Azospirilum are facultative anaerobes. Therefore, they can live without oxygen if necessary. They are A. melinis, A. thiophilum, and A. humicireducens. In addition, the growth temperature of Azospirilum is 5°C and 42°C and in substrates with a pH of 5 to 9, with optimal growth occurs around 30°C and 7 pH. Microbiologists use nitrogen-free semi-solid media to isolate Azospirilum from samples.  

What is Azotobacter

Azotobacter is a genus of Gram-negative bacteria that lives in neutral and alkaline soils, in water, and in association with some plants. It is a motile and oval or spherical shape bacterium. Moreover, Azotobacter forms cysts with thick walls and large quantities of capsular slime. Usually, Azotobacter is aerobic.

Figure 2: Azotobacter

Azotobacter is important as a nitrogen-fixing bacteria that converts atmospheric nitrogen into ammonium ions. In addition to that, Azotobacter is important for the production of biofertilizers. It is also important for the production of food additives and some biopolymers.   

Similarities Between Azospirillum and Azotobacter

• Azospirilum and Azotobacter are two types of Gram-negative bacteria.
• Both fix nitrogen.
• Moreover, they are free-living bacteria that promote plant growth.

Difference Between Azospirillum and Azotobacter

Definition

Azospirillum refers to a Gram-negative, microaerophilic, non-fermentative, and nitrogen-fixing bacterial genus from the family of Rhodospirillaceae, while Azotobacter refers to any of a genus of large rod-shaped or spherical bacteria occurring in soil and sewage and fixing atmospheric nitrogen.

Family

Azospirilum belongs to the Azospirillaceae family while Azobacter belongs to the Pseudomonadaceae Family.

Significance

Usually, Azosprillum is microaerophilic and surface colonizing bacteria while Azotobacter is an aerobic, soil-dwelling bacteria.

Oxygen Requirement

Azospirilum is aerobic, but is also microaerophilic and can survive in low oxygen conditions, while Azotobacter is an aerobic bacterium and require high oxygen concentration for them to function.

Growing Temperature

Azospirilum grows 5°C to 42°C while Azotobacter grows 20°C to 30°C.

Shape

Azospirilum is an oblong-rod-shaped bacterium while Azotobacter is an oval or spherical-shaped bacterium.

Cysts Formation

Moreover, Azospirilum does not form cysts while Azotobacter forms cysts for survival from harsh conditions.

Importance

At lower oxygen concentrations, Azospirlum converts inert nitrogen into biologically usable forms while Azotobacter releases ammonium ions from the fixation of nitrogen into the soil.

Conclusion

In brief, Azospirilum is a genus of bacteria that is microaerophilic. Under low oxygen concentrations, this bacterium converts inert nitrogen into biologically usable forms. On the other hand, Azotobacter is another genus of bacteria that fix inert nitrogen into ammonium ions. However, Azotobcter is aerobic. Thus, the main difference between Azospirilum and Azotobacter is their oxygen requirement.    

References:

1. Wikimedia Foundation. (2022, May 3). Azospirillum. Wikipedia. Retrieved August 27, 2022
2. Wikimedia Foundation. (2022, March 22). Azotobacter. Wikipedia. Retrieved August 27, 2022

Image Courtesy:

1. “Azo pic” By TAToennisson- Own Work (CC BY-SA 4.0) via Commons Wikimedia
2. “Azotobacter cells” By DAN H. JONES – Own Work (Public Domain) via Commons Wikimedia