Rhizobium

Rhizobium is a genus of bacteria associated with the formation of root nodules in legumes. They are known for their role in nitrogen fixation, a process that converts atmospheric nitrogen into a usable form for plant growth.

Overview

Rhizobium bacteria are Gram-negative, non-sporulating rods. They are found in the soil and after infection, produce nodules in the legume root system. These nodules act as factories for nitrogen fixation, converting atmospheric nitrogen into ammonia, which is then used by the plant for growth and development.

Nitrogen Fixation

Nitrogen fixation is a process by which nitrogen in the atmosphere is converted into ammonia. This process is essential for life because fixed nitrogen is required to biosynthesize the basic building blocks of life, e.g., nucleotides for DNA and RNA and amino acids for proteins. Nitrogen fixation is carried out naturally in the soil by a wide range of microorganisms termed diazotrophs, which includes bacteria such as Azotobacter, and archaea. Some nitrogen-fixing bacteria have symbiotic relationships with plant groups, especially legumes.

Symbiosis

The symbiotic relationship between Rhizobium and legumes is of significant agricultural value as it can enhance soil fertility without the need for chemical fertilizers. The bacteria colonize plant cells within root nodules, where they convert atmospheric nitrogen into ammonia, a form of nitrogen that the plant can use for growth and development.

Species

There are several species of Rhizobium, including Rhizobium leguminosarum, Rhizobium etli, and Rhizobium gallicum. Each species has a specific range of legume hosts with which it can form a symbiotic relationship.

See also

• Nitrogen cycle
• Legume
• Symbiosis
• Bacteria

Rhizobium

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  Rhizobium tropici strain BR816 on TY agar