Rhizobia

Rhizobia are Gram-negative soil bacteria which grow inside the root nodules of legumes (the pea family: Fabaceae). 

The growth of this bacteria is beneficial to their plant host. They fix (absorb and chemically change) nitrogen from the air and convert it into the chemical ammonia (through the help of enzymes). The host plant breaks down this ammonia and uses it for growth.  

In return, the plants provide the bacteria with nutrients for growth from products of plant  photosynthesis. 

Rhizobia require a plant host; they cannot independently fix nitrogen. As this relationship is  beneficial for both plant and bacteria involved, it is a classic example of symbiosis and mutualism which are found in all Rhizobia.

Rhizobia is very important in aiding plant growth in soils with low Nitrogen concentrations and is classed as a fertiliser for soil.

 History 
Rhizobia was discovered by Martinus Willem Beijerinck in 1888.

The word rhizobia comes from the Ancient Greek "ῥίζα" (rhiza) for root and "βίος" (bios) for life.

 References 

Category:Plant physiology
Category:Gram-negative bacteria