What is the Difference Between Rhizobium and Bradyrhizobium

The main difference between Rhizobium and Bradyrhizobium is that Rhizobium shows fast growth, whereas Bradyrhizobium shows slow growth.  

Rhizobium and Bradyrhizobium are two genera of microorganisms that fix nitrogen from the atmosphere. They are Gram-negative bacteria important in the Nitrogen cycle.  

Key Areas Covered

1. What is Rhizobium
– Definition, Structure, Function
2. What is Bradyrhizobium
– Definition, Structure, Function
3. Similarities Between Rhizobium and Bradyrhizobium
– Outline of Common Features
4. Difference Between Rhizobium and Bradyrhizobium
– Comparison of Key Differences

Key Terms

Bradyrhizobium, Rhizobium

What is Rhizobium

Rhizobium is a genus of Gram-negative bacteria that fix atmospheric nitrogen. They are especially soil bacteria that form endosymbiotic relationships with legumes and other flowering plants. They colonize in roots of plants to form root nodules. Also, nitrogenase is the enzyme that involves in the conversion of atmospheric nitrogen to ammonia. Importantly, the forming ammonia is shared with the host plant for the nutritional requirements, and plants supply nutrition such as organic compounds to the bacterium. Plants produce organic compounds from photosynthesis. Additionally, forming a mutual relationship is known as rhizobia. The forming rhizobia serves as a natural fertilizer for the plant.

Figure 1: Rhizobium

Furthermore, Rhizobium belongs to the family Rhizobiaceae. Rhizobium rhizogenes is a genus that severely alters the development of plants inducing the formation of hairy roots. Therefore, Rhizobium can alter plant development. Further, this genus contains aerobic bacteria that are rod-shaped. Also, many species of Rhizobium are able to fix nitrogen. Additionally, they form symbiotic relationships with plants.

What is Bradyrhizobium

Bradyrhizobium is another Gram-negative bacterium that belongs to the family Nitrobacteraceae. It is a bacillus bacterium that is rod-shaped. It also contains a subpolar or polar flagellum. On the other hand, Bradirhizobium is a soil bacterium. Similar to Rhizobium, Bradirhizobium forms symbiotic relationships with leguminous plants. it fixes atmospheric nitrogen to ammonia required for plant growth. Instead, plants provide carbohydrates for the growth of the bacterium Bradyrhizobium.

Figure 2: Root Nodules

Moreover, one of the main characteristic features of Bradyrhyzobium is the slow growth of the bacterium, but on the contrary, Rhizobium grows fast. Although Bradyrhizobium belongs to the family Nitrobacteraceae, it fixes atmospheric nitrogen into ammonia. However, the bacteria in the family Nitrobacteraceae converts ammonia into nitrites. In the root of plants, Bradyrhizobium occurs in the root nodules. Rhizobia moves toward the plants and attaches to the root hairs. Then, plants release flavonoids that express nod genes in the bacteria. It secretes an enzyme, Nod factors, curling the root hair along with rhizobia.

Similarities Between Rhizobium and Bradyrhizobium

• Rhizobium and Bradyrhizobium are two genera of nitrogen-fixing bacteria.
• They fix nitrogen from atmospheric nitrogen.
• Therefore, they are important in the Nitrogen cycle.
• They are rhizobia that fix atmospheric nitrogen into ammonia.
• They are Gram-negative bacteria.
• Importantly, they form endosymbiotic relationships with legumes and other flowering plants.
• They are aerobic bacteria.
• They are rod-shaped bacteria.
• Also, they occur in soil.

Difference Between Rhizobium and Bradyrhizobium

Definition

Rhizobium refers to a genus of Gram-negative soil bacteria that fix nitrogen, while Bradyrhizobium refers to the symbiotic bacterium that can form nitrogen-fixing nodules on legumes.

Family

Rhizobium belongs to the family Rhizobiaceae, while Bradyrhizobium belongs to the family Nitrobacteraceae.

Growth

Rhizobium shows fast growth, while Bradyrhizobium shows slow growth.

Conclusion

In brief, Rhizobium and Bradyrhizobium are two genera of nitrogen-fixing bacteria. They fix atmospheric nitrogen into ammonia. Also, they are Gram-negative bacteria. Rhizobium belongs to the family Rhizobiaceae, and it shows fast growth. In comparison, Bradyrhizobium belongs to the family Nitrobacteraceae, and it shows slow growth. Therefore, the main difference between Rhizobium and Bradyrhizobium is their growth rate.

References:

1. Rhizobium. Rhizobium – an overview | ScienceDirect Topics. (n.d.). https://www.sciencedirect.com/topics/immunology-and-microbiology/rhizobium
2. Wikimedia Foundation. (2023m, May 12). Bradyrhizobium. Wikipedia. https://en.wikipedia.org/wiki/Bradyrhizobium

Image Courtesy:

1. “Agrobacterium-tumefaciens” By A. G. Matthysse, K. V. Holmes, R. H. G. Gurlitz – Own work (Public Domain) via Commons Wikimedia
2. “Root-nodule01” By Louisa Howard – Dartmouth Electron Microscope Facility – Own Work (Public Domain) via Commons Wikimedia